SUDAN AGADEMY OF SGIENGES(SAS)

ATOMIC EhTERGY RESEARCHES COORDII\rATI ONCOUNCIL

- Development of Chemical Dosimeters

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A dissertation Submitted in a partial Fulfi l lment of theRequirement fbr Diploma Degree in Nuclear Science

(Chemistry)

Fareed Fadl Alla Mersani

Supervisor Dr K.S. Adam

By

Murch 2006

SUDAN ACADEMY OF SCIENCES(SAS)

ATOMIC ENERGY RESEARCHES COORDINATIONCOUNCIL

Development of Chemical Dosimeters

A dissertation Submitted in a partial Fulfillment of theRequirement for Diploma Degree in Nuclear Science

(Chemistry)

By

Fareed Fadl Alla Mergani

Supervisor Dr K.S. Adam

March 2006

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CONTENTS

Subject Page

Dedication..... IAcknowledgement .. .. IIAbstract III

DosimefryLntroductionPrinciple of DosimetryDosimefiy Systemsprimary standard dosimeters

l-3-Z Reference standard dosimeters ... ..Transfer standard dosimeters ... ...Routine dosimetersMeasurement of absorbed dose .Calibration of Dosimetrv svstemTransit dose effects

Requirements of chemical dosimetersIntroductionDeveloping of chemical dosimetersClassification of Dosimetry methodsRequiremsnts of ideal chemical dosimetersTypes of chemical systemLiquid aqueous systemsPrerequisites of chemical Dosimety

Purification of water

Treaftnent of glass ware and irradiation cellsTreatrnsnt of plastic irradiation cellsUse of irradiation cells .Stabilizing AgentsDefinition of G value

Ch-3 Types of aqueous chemical dosimeters3-I Fricke dosimeter3-l-1 Principle

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2323243-l-2 Basic reactions

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CONTENTS

Subject Page

- Dedication... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... IAcknowledgement ... '" ... ... ... ... ... ... '" ... ... ... ... '" ... '" ..... 11Abstract ... ... ... '" ... ... ... '" ... ... ... ... -..... ... ... ... ... ... ..... III-

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Ch-l1-11-21-31-3-11-3-21-3-31-3-41-41-51-6

DosimetryIntroduction .Principle of Dosimetry '" '" .Dosimetry Systems .primary standard dosimeters '" .Reference standard dosimeters " .Transfer standard dosimeters '" .Routine dosimeters .Measurement of absorbed dose .Calibration ofDosimetry system '" .Transit dose effects .

1234445

668

Ch-22-12-22-32-42-52-62-72-7-1202-7-22-7-32-7-42-82-9

Requirements ofchemical dosimetersIntroduction ... . . . ... . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . 11Developing ofchemical dosimeters ... . .. .. . . . . . . . ... .. . . . . . 12Classification of Dosimetry methods. .. . . . . . . . . . . . . . . . . . . . .. ... 14Requirements of ideal chemical dosimeters ,. . . . 15

Types ofchemical system .. . . .. . . . . . . . . . .. 16Liquid aqueous systems. .. . . . . . . .. . . . . . . . .. . . . . . . . . . . . . . . . . . 17Prerequisites of chemical Dosimetry '" ... 19

Purification of water '" " .

Treatment ofglass ware and irradiation cells... . .. ... . 20Treatment ofplastic irradiation cells '" '" .. . .. 20Use of irradiation cells... ... ... ... ... ... 21Stabilizing Agents ... . . . .. . . . . . . . . . . .. . . . . . . . . .. .. . .. . . . . 21Defmition ofG value ... . . . . . . . .. .. . . . . .. . . . . . .. . . . . .. . . . 21

Ch-33-13-1-13-1-2

Types of aqueous chemical dosimetersFricke dosimeter '" '" '" ..Principle '" '" .Basic reactions '" .. . .. . . .. . .. .. . .. . .. . . . . . .. . ..

232324

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3-l-3 Calculation of the absorbed dose . 243-l-4 Influence of various factors 263-2 Ceric sulphate (Ceric - Cerous) dosimeter 283-2-l Principle 293-2-2 Calculation of absorbed dose 293-2-3 lnfluence of various factors 303-3 Other aqueous qystems 303-3-l Aromatic solutes Systems 303-3-2 Chlorinated hydrocarbon Solutes 313-4 Potential liquid dosimeters ... .. 313-5 Gaseous chemical dosimeters ..... 323-6 Solid chemical dosimeters ... . . ... ... ...32

ConclusionReferences

LIST OF TABTES

Table (1) :Table (2) :

Various Radiation Dosimetrv standardsEvents in Radiolysis of aqueous solutions.

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3-1-3 Calculation of the absorbed dose 243-1-4 Influence ofvarious factors 263-2 Ceric sulphate (Ceric - Cerous) dosimeter 283-2-1 Principle 293-2-2 Calculation of absorbed dose...... 293-2-3 Influence ofvarious factors... 303-3 Other aqueous systems 303-3-1 Aromatic solutes Systems '" 303-3-2 Chlorinated hydrocarbon Solutes 313-4 Potential liquid dosimeters , '" 313-5 Gaseous chemical dosimeters " 323-6 Solid chemical dosimeters 32

Conclusion , 34References ... 35

LIST OF TABLES

Table (1): Various Radiation Dosimetry standards 6Table (2): Events in Radiolysis of aqueous solutions... .. 19

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To those who are donate me their live...To those who are lighten my way by candles...To those who are learned me and guided me...

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ACKNOI|TLEDGE|lJ|ENTI thank GOD too mush that I could complete this

L beneficial work after a lot of effort and constraintsthat faced me.

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I deeply grateful to all those who helped me in1' achieving this research

I Many thanks for Sudanese Atomic EnergyCommission (S.A.E.C) Staff for their advises.

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Also full thanks for my supervisor Dr K.S.ADAM-- for suggested idea and orientation and for his valuable

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ACKNOWLEDGEMENTI thank GOD too mush that I could complete this

beneficial work after a lot of effort and constraintsthat faced me.

I deeply grateful to all those who helped me inachieving this research

Many thanks for Sudanese Atomic EnergyCommission (S.A.E.C) Staff for their advises.

Also full thanks for my supervisor Dr K.S.ADAMfor suggested idea and orientation and for his valuable

guidance through out the research.

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Affi AOTA chemical dosimeter is a systern that meazures the energy by virtue of

chemical changes from ionizing absorbed radiation produced unit when it

is exposed to ionizing radiation. In all chemical dosimeters radiation

induced chemical reaction produces at least one, initially absent species,

which is properties long lived enough to determine its quantity or the

change in the initial systems. Different types of chemical dosimeters were

discussed such as aqueous, gaseous and solid, but the great consideration

was given to aqueous systems because of their vital role in setting many

processes.

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A chemical dosimeter is a system that measures the energy by virtue of

chemical changes from ionizing absorbed radiation produced unit when it

is exposed to ionizing radiation. In all chemical dosimeters radiation1

induced chemical reaction produces at least one, initially absent species,

which is properties long lived enough to determine its quantity or the

change in the initial systems. Different types ofchemical dosimeters were

discussed such as aqueous, gaseous and solid, but the great consideration

was given to aqueous systems because of their vital role in setting many

processes.

III

ilI{APTER ONEl.DOSIMETRY' l -

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APTERONEI-DOSIMETRY

1 -1 Introduction:

Use of ionizing Radiation has become increasingly important in a different

fields, industrial processing applications such as polymer cross linking,

polyrner degradation, polymer grafting, vulcanrzation, curing of coating,

scrubbing of gaseous effluents, sterilization of medical products, sewage

sludge hygienisation, delayed ripening of fruits, sprout inhibition and insect

population control. The absorbed doses employed in these applications range

from 10 Gy - more than 100 kcy). 2

In the use of ionizing Radiation, reproducible and an accurate irradiation of

the products to get desirable effects depends on having reliable dosimetry

systems. Dosimetry play a vital role in setting of process parameters to meet

variety of specifications, dose mapping in products, carrying out validation,

commissioning procedure as well as in the day today operation of the plant.

Measuring response of dosimeter to Radiation is generally much easier and

quicker to measure than any other parameter of the product that has been

irradiated. Documentation of dose is often required in order to ensure

operational safety quality control. 2

The effects of Radiation on the matter depend on the Radiation field, as

specified by the Radiation quantities and on the interactions between

Radiation and matter, as characterized by the interaction quantities.

Dosimetric quantities are products of radiometric quantities and interaction

coefficients. Radiation interacts with matter in a series of processes in which

particle energy is converted and finally deposited in matter. Measurement of

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1 -1 Introduction:

Use of ionizing Radiation has become increasingly important in a different

fields, industrial processing applications such as polymer cross linking,

polymer degradation, polymer grafting, vulcanization, curing of coating,

scrubbing of gaseous effluents, sterilization of medical products, sewage

sludge hygienisation, delayed ripening of fruits, sprout inhibition and insect

population control. The absorbed doses employed in these applications range

from 10 Gy - more than 100 kGy). 2

In the use of ionizing Radiation, reproducible and an accurate irradiation of

the products to get desirable effects depends on having reliable dosimetry

systems. Dosimetry play a vital role in setting of process parameters to meet

variety of specifications, dose mapping in products, carrying out validation,

commissioning procedure as well as in the day today operation of the plant.

Measuring response of dosimeter to Radiation is generally much easier and

quicker to measure than any other parameter of the product that has been

irradiated. Documentation of dose is often required in order to ensure

operational safety quality control. 2

The effects of Radiation on the matter depend on the Radiation field, as

specified by the Radiation quantities and on the interactions between

Radiation and matter, as characterized by the interaction quantities.

Dosimetric quantities are products of radiometric quantities and interaction

coefficients. Radiation interacts with matter in a series of processes in which

particle energy is converted and finally deposited in matter. Measurement of

1

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the energy absorbed per unit mass in a medium exposed to ionizing

Radiation necessitates the introduction of a dosimeter into the medium.

Dosimeter is a device that, when irradiated, exhibits a quantifiable changes

in some property of the device which can be related to the absorbed dose in a

given material using appropriate analytical instrumentation and techniques.

Different tlpes of dosimeters like gaseous ionization chambers, thin films,

solids and liquids are used in Radiation dosimetry. There is a considerable

variation in their size and composition. Also several wall materials having

varying thickness are used to contain the dosimeter. 2

l-2 Principles of Dosimetry:

The dose in a medium is measured by replacing the medium by a dosimeter.

Normally, dosimeter will differ from the medium in both atomic number and

density and it therefore, constitutes a discontinuity, which will be referred to

as activity. The energy absorbed in the dosimeter is therefore not the same as

that absorbed by the medium. Under electronic equilibrium conditions, the

dose in the medium can be estimated using cavity (Bragg GraD theory. (2)

For irradiations using a photo-source, the dosimeter may be considered as

activity in the material of interest, and the interpretation of absorbed dose in

material as follows. If the sensitive region of the dosimeter is very thin

compared to the range of the highest energy secondary electrons, then most

of the energy deposited in the dosimeter and in the material surrounding it

results from secondary electrons produced outside the dosimeter (that is, in

the equilibrium layer of material). Thus the absorbed dose in the material 2

, Dr[, is given by:

Dm = 6l P)m ,n

(s I P)d

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the energy absorbed per unit mass III a medium exposed to ionizing

Radiation necessitates the introduction of a dosimeter into the medium.

Dosimeter is a device that, when irradiated, exhibits a quantifiable changes

in some property of the device which can be related to the absorbed dose in a

given material using appropriate analytical instrumentation and techniques.

Different types of dosimeters like gaseous ionization chambers, thin films,

solids and liquids are used in Radiation dosimetry. There is a considerable

variation in their size and composition. Also several wall materials having

varying thickness are used to contain the dosimeter. 2

1-2 Principles of Dosimetry:

The dose in a medium is measured by replacing the medium by a dosimeter.

Normally, dosimeter will differ from the medium in both atomic number and

density and it therefore, constitutes a discontinuity, which will be referred to

as activity. The energy absorbed in the dosimeter is therefore not the same as

that absorbed by the medium. Under electronic equilibrium conditions, the

dose in the medium can be estimated using cavity (Bragg Gray) theory. (2)

For irradiations using a photo-source, the dosimeter may be considered as

activity in the material of interest, and the interpretation of absorbed dose in

material as follows. If the sensitive region of the dosimeter is very thin

compared to the range of the highest energy secondary electrons, then most

of the energy deposited in the dosimeter and in the material surrounding it

results from secondary electrons produced outside the dosimeter (that is, in

the equilibrium layer of material). Thus the absorbed dose in the material 2

, Dm, is given by:

Dm = (SIP)m Dd(SIP)d

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Where (sf t ' )m ancl (SlP)d are mass col l is ion stoppirrg powcr l i r r the

st t r rounding nrater ia l ancl dosir lcter ' . rcspect ivel ; , . l )d ls absorbecl dose ip

the dosimeter. l f the sensi t ive rcgion ol- t l ie c losir letcr l ras a th ickncss uruclr

greater than the I 'ange of the highesl energy sccorrc larv c lcct lnns. lhor rn11sl

of the energy de posi tecl in i t resul ts 1l 'or l thc scconclarv elcctrons proclucecl

wi th in the dosinreter i t sel l , t l r r , rs , the absorbed dose in the rnater iz i l is q ivcnr 2O V :

I)rt = 0y4!!,, D,l(per t , P)c l

Where (1-rcnf I))nt ar'r4v l lrcnf1')r/ ' ,, ' . thc nrass absorpti.n coelflcierrts of thc

ntediutn, / t / a l td the dosimetcr tnertcr ia l , / , resl lect ively. I f thc scnsi t ivc

region of t l ie dosi tneter has a t l r ic l<ncss betwecn thc two l i rn i ts. thqr lhe

above two ecl t tat ions may l re cornbirrccl rv i th approl t r iatc u 'e isht i l tg thctors to

re f lec t the re la t i ve co t r t r ibu t io t rs o l ' cach tc rn t ( l Jur l in 's gcnera l ( 'av i ty ' thcur .y

l 'he col l is ion stopping powcrs ancl l l re crrcr .g) , absor. l ) t iorr cocl- l lc icnts ar-c

energy dependent: however lor hoiv atornic nr.rrr rbcr rrratcr ia ls arrc l f or t l rc

el lergy range 0.1 to l0 MeV. thc rat ios of ' thc stol ' r l t i r ru powcl 's l r rd cncluy

absorpt ion cocf ' l lc ients c lc l I )oI var '1, s igrr i l icant l_1, as a l i rnct iorr o l 'cncrs-r , .

A l tho t rgh th is de f i l t i l i o t r i s g ivcn s l r ' i c t l v lo r i r t rsorbcc l r losc a t a po i r r l i r r

I {adiat ion absorbing trrater, i t is gerreral ly avclagccl o l 'cr a l j r r i tc nrass ul 'u

given nrater ia l , thc absorbecl c lose bcirrg r"cacl b1,a c losinrctcr cal ibratc i r r

terms of energy i rnparted per r . rn i t rnass of 'a givcn r latcr iar l . ln l {acl iat iorr

processi t rg, the rcferetrce tnater ia i in nrosl cal ibrat ion is r ,vatcr , i t is i rnpo11alr

to real ize that the dosimetet ' is intendecl to givc nrcasurcrnerr t o l 'absor.bccl

dose averagecl t lver a smal l volurne. - l -he

s ignal Iorrrr th is c lc ls i r r rctcr carr

therefore be a tneasttre of encrgy absorbccl in that volrrrnc. vvhich can bc

related to the c lose in the proclLrct . 2

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Where (S /1')//1 and (S'/ P)d are mass collision stopping power for the

surrounding material and dosimeter. respectively. Dd Is absorbed dose in

the dosimeter. I f the sensitive region of the dosimeter has a thickness much

greater than the range of the highest energy secondary electrons, then most

of the energy deposited in it results from the secondary electrons produced

within the dosil11eter it selC thus, the absorbed dose in the material is given

by: 2

Dill = (pen/ PJ!!2 Dd(pen/P)d

Where (I-ten/P)17I and (pen/ jJ)d arc the mass absorption coefficients of the

medium, 11/ and the dosimeter material d ,respectively. If the sensitive

region of the dosimeter has a thickness between the two limits, then the

above two equations may be combined with appropriate weighting f~tctors to

ref1ect the relative contributions of each term (Burlin's general Cavity theory

The collision stopping powers and the energy nbsorption coefficients arc

energy dependent; however for how atomic number materials and 1'01' the

energy range 0.1 to 10 MeV, the ratios of the stopping powers and energy

absorption coefficients do not vary signi ficantly as a function of energy.

Although this definition is given strictly for absorbed dose at a point ill

Radiation absorbing mater, it is generally averaged over a finite mass of a

given material, the absorbed dose being rend by a dosimeter calibrate in

terms of energy imparted per unit mass of a given material. In Radiation

processing, the reference material in 1110st calibration is water, it is important

to realize that the dosimeter is intended to give measurement of absorbed

dose averaged over a small volume. The signal form this dosimeter can

therefore be a measure of energy absorbed in that vulume. vvhich call be

related to the dose in the product. 2

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l -3 Dosi tnctry Systerns:

1 'hey are usecl to tneasut 'e absorbcd dosc. ' l -hcy

consist o1-thc dosirncters.

measurenrent instrunrents ancl thci l associzr tccl rc l -crcncc stanclalds. ancl

procedures Ibr the system's r"rsc. Dosir lctcrs nray bc c l iv idcd into forrr basic

classes according to the elccuracy of thc c losir lctrv s1'stcnrs ancl arcas i t l -

appl icat ions as lo l lows. 2

l-3- l Pr imary Starrdirrd Dosirncters:

Pr imary standard dosimelct 's arc establ ishccl ancl rnaintaincd by nat iorral

standards laborator ies for cal ibrat ion ol ' l {acl iut iorr cnvi lor . r rncnts ( l ie lc ls) ancl

other dosimetcr"s. these are ei thcr ionizat iorr charnbcrs or calor i r letcrs. ' l ' l rc

overal l l tncertai t r ly at thc staqc is 1 lo,"o (at()5ot 'o cs "starrc l i r rc l c lcviat iorr") . 2

l 3-2 l tefcrcnce Startdarr l Dosirnetcr 's' l 'hese

closi tneters usecl to cal iLr latc l tacl iat ion cnr, ' i rorrnrcnts ancl rout ine

closimeters, re l 'c t 'c t rcc statrc larc l c losirnctcrs nr[r) / a lso l rc Lrsccl as nrut i r rc

dos imcters . ' l ' hcsc are chcnr ica l c los i rnc t r ' l , sys tc rn rvhcrc rcs l )onsc no t on ly to

I tadiat ion br-r t to ot l tcr in l lucncing l i rcturs such as tcnr l - ' 'c1 'n11r lc ancl c losc: ra lc:

i s reproc lL rc ib lc anc l wc l l charac tc r iz .cc l . ' l ' hcy a rc c luss i l l cc l as 11 ,1)c : "A" a r rc l

type "B" . ' ] .hc type "A" c los i t t t c tc t ' s I i r r cxa tnp lc . I ; t ' i c l< r : . ( ' c r i c . r l i c l r ro r ru r tc .

ethanol-nronochlorotrctrzcnc sol t t t iotrs arc svstctrrs iv l rosc I {acl iat ion

c l ' re rn ica l response is c l ra rac tc l i s t i c o l ' a par t i cLr la r c l rc r r i ca l cornpos i t ion anc l

th is can bc guarantcccl , ccrtai t t lv to rv i th i r r a l -c l r , 1-rcrccnt. provic lcd a goocl

chern ica l p rac t icc i s f i r l l o rvcc l . ' l - ypc " l l " r los i rnc tc rs i r rc sys lcnrs u 'h ic l r

exh ib i ts h igh prec is ion bu1- havc to bc ca l ib ra tcc l aga i r rs t a s tanc la rc l h ighcr in

the ser ies . '1 -he i l l tac l ia t ion fcsponsc car r no t bc p rc r l i ca tcc l pLr rc l ; ,on thc

bas ic o f con ipos i t ion thc ovcra l l r rnccr ta i r r tv assoc ia lcc l rv i t l r rc l ' c rc r rcc

dosirrreters is about + 3o .2

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1-3 Dosimetry Systems:

They are used to measure absorbed dose. They consist or the dosimeters.

measurement instruments and their associated relcrence standards, and

procedures for the system's use. Dosimcters may be divided into four basic

classes according to the accuracy of the dosimetry systems and areas or

applications as follows. 2

1-3-1 Primary Stalllhud Dosimetcrs:

Primary standard dosimeters arc established and maintaincd by national

standards laboratories for calibration of Radiation environments (fields) and

other dosimeters, these are either ionization chambers or calorimeters. The

overall uncertainly at the stage is ± I% (at 95% er "standard deviation"). 2

13-2 Reference Standard Dosimetcl's

These dosimeters used to calibrate Radiation environments and routine

dosimeters, reference standard dosimeters may <llso be used as routine

dosimeters. These are chemical dosimetry system where response not only to

Radiation but to other inlluencing factors such as temperature <lIld dose rate

is reproducible and well characterized. They arc classilied as type "A" and

type "13". The type "1\" dosimeters l()r example. Fricke, eeric. dichroll1ate.

ethanol-monochlorobenzene solutions arc svstems whose Radiation

chemical response is cltaracteristic of' a particular chcmiull composition and

this can be guaranteed, certainly to within a few percent, provided a good

chemical practice is followed. Type "13" dosimeters arc systems which

exhibits high precision but have to lx' cal ibrated against <1 standard higher in

the series. Their Radiation response can not be predicated purely on the

basic of composition the overall uncertainty associated with reference

dosimeters is about ± 3%. 2

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1-3-3 Transfcr Standnrd l )osi lne(e rs

Tl-rese are specizt l ly selcctecl c losinrctcrs usccl f i r r t rans{crr ing absorbccl c losc

inlbrmat ion f ronr accredi tcd or nat ional stanclarrc ls labur i r turv tc l an i r racl iat ion

lac i l i t y i t r o rdcr to cs tab l i shec l t raccab i l i t y {o r tha l lac i l i t l , . ' l ' l r csc c los in rc tc rs

shoulc l be usecl unclcr concl i t ions that are caref i r l lv control lccl b i r t l tc issLr ins

laboratory. f 'ratrsfer stiurclarcl closinrcte rs nray bc sclcctccl l i 'onr cit l icr

reference stanclard dositlctcrs or routinc closinrctcrs ancl shall havc

perforutancc character ist ics sucl t as long shcl l l i fb. casi ly cal i t r ratccl . stablc.

rugged, l tor tablc, t -nai l able, broacl absorbccl dosc langc. l lacl iat ion absor 'pt ion

propert ies s inr i lar to those of i r racl iat ion proclLrct . r 'c lat ivcly incxpcnsivc to

extremes of environnrental concl i t ions ,corrcctabIc st 's tcrnat ic crrors (c.g.

tetnperature, hr-rrnic l i ty , ctc) . proclLrciblc lots. r 'cpnrclrrc ib lc rcsl-ronsc ancl

snral l d imensions colxpal 'ccl to c l is tanccs ovcr rvhic l r atrsor i ' rccl c losc gracl icnts

becontc s isni f lcant. ctc. 2

l-3-4 l l.outinc l)osinrctcrs' they

nray be usecl lbr cpral i ty control arrc l l ) r 'occss nrorr i tor ins. I {out inc

dosimeters are systctns whosc pcr l i r r rnancc, part icLr l i t r ly l i , i th lcspcct to

environtnental inf l r tcrrc i t rg l i rctols, is not as goocl as t l rc l 'c l -crurcc systcnrs.

but whose case o1- usc ancl low cost nakcs thcrn i r lcal l i r r c lay l i i c la,r ,

mon i to r ing o f I {ad ia l io r r c loscs c lu r ing pr 'occsscs . ( ' r i l c r ia l i r r sc lcc l io r r o l '

rou t ine c los i r l c t ry sys tcn r inc luc lc su i tab i l i t y 'o f ' t l r t : c los in rc tc r ' { i r r t l r c

absorbed dose ratrgc ol ' intcrcst ancl l i r r usc wi th a s l )cci l ic l t roclLrct . sta["r i l i tv

anc l reproc iL rc ib i l i t y o l ' thc sys tcnr . casc o l ' sys tc rn ca l ib la t ion . t raccub i l i t l , o l '

systet l cal ibrat iorr to ni t t ional stanclarcls. abi l i tv to corr t r 'o l svstcn'r l 'csp() l rsc

lbr system unccrtaint ics. such as t l rosc causccl b1, 1" ' , . , ' ' , . ' 'a t r r rc uncl l r r r r r r ic l i t r , .

ease aud s in ip l i c i t y o f usc . ava i lab i l i t y o { - c los i rnc t t - r ' s ; i r r rcasonab l ) ' la lgc

- ~

- ~

- .....

- .....

- .....

- ...

- ....

- ....

- ....

- -'"

- -'to

- ....

------- ..--- ...

- ..- ...

.....

.... --

1-3-3 Transfer Standard Dosimetcrs

These are specially selected dosimeters used for transICrring absorbed dose

information from accredited or national standards laboratory to an irradiation

facility in order to established traceability for that f~lcil ity. These dosimcters

should be used under conditions that are carefully controlled by the issuing

laboratory. Transfer standard dosimeters may be selected from either

reference standard dosimeters or routine dosimeters and shall have

performance characteristics such as long shelf life, easily calibrated, stable,

rugged, portable, mail able, broad absorbed dose range, Radiation absorption

properties similar to those of irradiation product, relatively inexpensive to

extremes of environmental conditions ,correctable svstcmatic errors (e.g.• L

temperature, humidity, etc), producible lots, reproducible response and

small dimensions compared to distances over which absorbed dose gradients

become significant, etc. 2

1-3-4 Routine Dosimeters

They may be used for quality control and process monitoring. Routine

dosimeters are systems whose performance, particularly with respect to

environmental influencing f~lctors, is not as good as the reference systems,

but whose case of use and low cost makes them ideal for day to day

monitoring of Radiation doses during processes. Criteria for selection or

routine dosimetry system include suitability or the dosimeter for the

absorbed dose range of interest and for use with a specific product. stability

and reproducibility of the system, ea5e of system calibration, traceability of

system calibration to national standards, ability to control system response

for system uncertainties, such as t!lo5C caused by temperature <lIld humidity,

ease and simplicity of use, availability of dosimeters in reasonably large

5

cluant i t ies, overal l in i t ia l ancl operat ional cost c l l -systcrn i r rc lucl i r rq c losirnctcrs

readout equipnretrt ,ancl labor recluirccl fbr cklsiurctcr rcaclout ancl

interpretat ic ln. t ' r - rggedncss of thc s1,st t - 'nr rcsistancc to r lanrai tc c l r r r i r rg roLrt inc

hand l ing and usc in a p rocess ins cnv i ronnrcn l . c tc . . 2

fable ( I ) : Var ioLrs l {adiat ion c losirnclry standarcls

DosimetersI {out i rre Dosir leters ( 5?6) R"f.*,,r*-- Str""k, ' ,1;

Dosi rnetcrs (3%r)l)r'i rrI ) os

Plastics Fr ic l<c !gr( ' a l rDve o last ics Clcr ic- Clerous

(CTA) f ihns [ ) i chronru lcRadio chronic d) '" f l l rns

' f I -

dosimetersl r thano l r lonoch lo r 'obcnz .c r re u Ia r r inc

l -4 Measurenrent of absorbed t lose or t losc ratc

The reference soLrrce is cal ibratecl by mcans ol-onc ol ' thc l r r inrary stanclarcls

(e.g. graphi te calor inretr ic or standarcl izecl re l -crcncc urcthor is " f i l ic l tc

dosirnetry") and the closirneter signal is therr cclnvcrlccl to absortrccl cJosc or'

dosc t 'a (c in rva tc t ' l r1 ' ( '11111 l r l r t r t t i t r t t s t ' t r t sc r l t r t r ( ' i r v i l v th t ' r r r r ' . ' l ' l r t ' r ' r ' { i ' l t ' t r c i '

soL l l ' oc i s t rscc l to i r t ' l c l ia tc t l t c t 'o t t t inc r los i r r rc tc r i s r r r r t le r i t l c r r t i c i r l cor r t l i t i o r rs .

and the cal ibrat ion is r . tsual ly cxpressccl in tcrnrs ol 'c l i rsc ur c lc lsc ratc in t [c

dosimeter mecl iut 'n. fhe roul i t re c losi lneter is thcn cxl tosccl tc lgct l tcr q, i t I thc

produc t in the i r rac l ia t ion , fac i l i t l , . a l t i r< lugh thc i r ra r l ia t io r r conr l i t ions ( i . c .

el le l 'gy spectrunr erncl gconrctry) ntay t re ntar.kcr l l ) , c l i l ' lcr-cnt l l .or t r thosc ol ' thc

cal ibrat ion. 2

I -5 Ca l ib ra t ion o l 'Dos in rc t l ' l svs le lns

Cal ibrat ion ver i f lcat ion is pcrfonnecl pcr iocl ical ly to corr f l r ru 1hc cont inrrcr l

val id i ty of thc cal ibrat ic ln curve. [ {ourt inc dosinrctry s l ,stc lns cztn bc

i rrrctcrs ( l-2'1,1,)zi t t iort c lr iur l rcr '

-. ~

. ~

quantities, overall initial and operational cost orsystcm including dosimeters

readout equipment ,and labor required ror dosimeter readmit and

interpretation, ruggedness or the system resistance to damage during routine

handling and use in a processing environment, etc .. 2

Table (1): Various Radiation dosimctry standards

'1lllary Standardsosil11eters (1-2(~(l)

nizatioll chambera lori Illeters

Dosimeters.-- ---

Routine Dosimeters (5%) Reference Standards PIDosimeters (3(Xl) !)

Plastics Fricke 10Dye plastics Ceric- Cemus C(eTA) films Dichromate

-- ._- ---

Radio chronic dye films TL Ethanol monoch lor-dosimeters obenzene alanine

1-4 Measuremcnt of absorbcd dose or dose ratc

The reference source is calibrated by means of onc of the primary standards

(e.g. graphite calorimetric or standardized reference methods "Fricke

dosimetry") and the dosimeter signal is then converted to absorbed dose or

dose rate in W\1ter b~' c()mputnti()n:-. bnsed on Cn\'i\\' \\w\)ry, TIl\' r\'!t'n'\\\'\'

source is lIsed to irradiate the routille dusillll'tl'l' is ulldn idclltic,t1 cUlldiliulls.

and the calibration is usually expressed in terms or dose or dose rate in the

dosimeter medium. The routine c10simeter is then exposed together with the

product in the irradiation, facility, although the irradi<ltion conditions (i.e.

energy spectrum and geometry) may be markedly di JTcrent II'om those or the

calibration. 2

1-5 Calibration of Uosimctry systcms

Calibration verification is perrormed periodically to conllrm the continued

validity of the calibration curve. Routine dosimetry systems can be

6

t_ .

-

t

t - ,

t

-

t

-

t

calibrated by irradiation at high dose Radiation dosimetry calibration

laboratory, an in- house calibration facility whose dose rates have been

demonstrated to be traceable to appropriate nationai standard or irradiation

of reference or transfer standard dosimeters with routine dosimeters in the

production irradiation facility. All possible factors that may affect the

response of dosimeters, including environmental conditions and variations of

such conditions within a processing facility should be known and taken in to

a count.

For each absorbed dose point, use number of dosimeters required to achieve

the desired confidence level. The number of dosimeters, n, required to

estimate the dosimeter response at a given absorbed- dose level is based on

the determination of a two sided confidence interval that is expected to

bracket the true mean response y6,100 (l- a)% of the time. In order to

determine the mean response, y6, within + 5oh at a95oh confidence level, the

number of dosimeters required for absorbed dose level is

t 7 s z

" =

(oLoEiC

Where .s is the estimate of the standard deviation of the response

distribution within a batch of random sample of dosimeters and r is the

student's distribution. 2

The number of sets of dosimeters required to determine the calibration curve

of the dosimetry system depends on the absorbed- dose range of utilization.

Use at least five sets or each factor of ten span of absorbed dose, or at least

four sets if the rang of utilization is less than a factor of ten. Position the

dosimeters in the calibration curve Radiation field in a defined, reproducible

location. The variation in absorbed dose rate within the volume occupied by

the dosimeter should be within+lo/o of the averase value.

•.........

•.........

.-~ ..

............

.-

I.......

.-

.........

.-

I.......

..-

-1--__

..

---

..

calibrated by irradiation at high dose Radiation dosimetry calibration

laboratory, an in- house calibration facility whose dose rates have been

demonstrated to be traceable to appropriate national standard or irradiation

of reference or transfer standard dosimeters with routine dosimeters in the

production irradiation facility. All possible factors that may affect the

response of dosimeters, including environmental conditions and variations of

such conditions within a processing facility should be known and taken in to

a count.

For each absorbed dose point, use number of dosimeters required to achieve

the desired confidence level. The number of dosimeters, n, required to

estimate the dosimeter response at a given absorbed- dose level is based on

the determination of a two sided confidence interval that is expected to

bracket the true mean response Yo,1 00 (1- a)% of the time. In order to

determine the mean response, Yo, within ± 5% at a 95% confidence level, the

number of dosimeters required for absorbed dose level is

Where S IS the estimate of the standard deviation of the response

distribution within a batch of random sample of dosimeters and t is the

student's distribution. 2

The number of sets of dosimeters required to determine the calibration curve

of the dosimetry system depends on the absorbed- dose range of utilization.

Use at least five sets or each factor of ten span of absorbed dose, or at least

four sets if the rang of utilization is less than a factor of ten. Position the

dosimeters in the calibration curve Radiation field in a defined, reproducible

location. The variation in absorbed dose rate within the volume occupied by

the dosimeter should be within ±1% of the average value.

7

I t

j

When using galnma- ray source or X-ray beam for calibration surround thedosimeter with a sufficient amount of material to achieve approximate

electron equilibrium conditions. The appropriate thickness of such materialdepends on the energy of the Radiation. 2

For measurement of absorbed dose in water, use material that have Radiation

absorption properties essentially equivarent to water for example 60co

source' 5nm of solid poly styrene (or equivalent polymeric material) shouldsurround the dosimeter in all directions. Monitor and control temperature

and humidity during calibration. 2

1-6 Transit Dose effects:

Transit dose effect occur when the timing of calibration irradiation dose not

take into account, the dose received during the movement of the dosimeters

into and out of the irradiation position for example the timer on gamma cell-type irradiation dose not start until the sample chamber reaches the fully

down (irradiate) position. Some dose is received as the drawer goes down

and after the irradiation as the drawer goes up that is not accounted for in thetimer setting. This transit dose can be significant for low dose irradiations

and should be determined experimentally and incorporated into a formula for

calculating timer settings. For determining transit dose, a series ofincremental inadration times that started as clos e to zero selected,, with

specific dosimetry system employed. Five different inadiation times were

used. The results analyzed using linear regression analysis. A graph of theresults looked similar to following diagram: 2

J

...-.

•- ..--

...

-...

--41

~

....-

...

--...

-...

...

When using gamma- ray source or X-ray beam for calibration surround the

dosimeter with a sufficient amount of material to achieve approximate

electron equilibrium conditions. The appropriate thickness of such material

depends on the energy of the Radiation. 2

For measurement of absorbed dose in water, use material that have Radiation

absorption properties essentially equivalent to water for example 60CO

source, 5nm of solid poly styrene (or equivalent polymeric material) should

surround the dosimeter in all directions. Monitor and control temperature

and humidity during calibration. 2

1-6 Transit Dose effects:

Transit dose effect occur when the timing of calibration irradiation dose not

take into account, the dose received during the movement of the dosimeters

into and out of the irradiation position for example the timer on gamma cell­

type irradiation dose not start until the sample chamber reaches the fully

down (irradiate) position. Some dose is received as the drawer goes down

and after the irradiation as the drawer goes up that is not accounted for in the

timer setting. This transit dose can be significant for low dose irradiations

and should be determined experimentally and incorporated into a formula for

calculating timer settings. For determining transit dose, a series of

incremental irradiation times that started as close to zero selected, with

specific dosimetry system employed. Five different irradiation times were

used. The results analyzed using linear regression analysis. A graph of the

results looked similar to following diagram: 2

8

The intercept with Y- axis gives the value of the transit dose. To provide a

correction factor for all future irradiations, convert the transit dose by the

current dose rate. Subsequent timer settings can be calculated using the

formula:

Where D, is the target dose and r is the timer setting required achieving

that dose 2.

! - D, , at a given time , l, is given by

t-

Ir-T-

(.) 200a

100

100 200 300

Time of irradiation (min)

T- D ' - r ,D

l -I

Since the absorbed dose rate, D due to galnma ray emission by a Radioactive

nuclide source also varies exponentially with the decay time r, the dose rate,

9

-.

_A

-...

- ....

300

400 ~----------------~---,

300,-.>-

Cl--(l) 200rJ:J00

100 ...........................

0100 200

- ....

- ...

- ....

- ...

Time of irradiation (min)

.. ...

.. ...

The intercept with Y-axis gives the value of the transit dose. To provide a

correction factor for all future irradiations, convert the transit dose by the

current dose rate. Subsequent timer settings can be calculated using the

formula:

..... T=Dt--ID t

Where D t is the target dose and 1 is the timer setting required achieving

that dose 2.

Since the absorbed dose rate, D due to gamma ray emission by a Radioactive

nuclide source also varies exponentially with the decay time 1 , the dose rate,

~ .A

I

l~

rr~

r=

D t , at a given time, I, is given by

9

dose varies inversely with the dose rate and source activity, and is given by

/-^\ (rs)(75 f, = -:------11

e

Where (fs) is the timer setting necessary to deliver the required target dose

IL-

L -

D, = Dor-'' '

Where D,the dose rate is at a time,Do is the dose rate at some earlier

time(r=o). The timer setting,Zs necessary to deliver the targeted central

at timer, (rs), is the timer sitting at some earlier time,r=0 to deliver the

same tarset dose 2

t-

10

- ..

- ...

- .- ...

_. AI

_...

_. "'"

- AI

- ~

- ,lID

- ....

Where D( the dose rate is at a time, Do is the dose rate at some earlier

time (t = 0). The timer setting, TS necessary to deliver the targeted central

dose varies inversely with the dose rate and source activity, and is given by

(TS} = (T~)oe

Where (TS)/ is the timer setting necessary to deliver the required target dose

at timet, (TS)o is the timer sitting at some earlier time, t =0 to deliver the

same target dose 2

~ ..

L ....-....- 10~ ..

l ..

[

- 1

i ' {

r*I

I

\ -

t*L -

fltIAPTERT\VO2- RE,QUIREMENTS OF CHEMICAL DOSIMETERS

.....

.. ...

. .

- ..

- ..

............

- ..

~ -

l .

IIAPTERTWO2- REQUIREMENTS OF CHEMICAL DOSIMETERS

L- ' -

: rrl

r--L,

L T

t-:t,

t-:

2-1. Introduction:

The first chemical dosimeters were crude systems which changed color on

exposure to the relatively soft x- rays then being used medically. Barium

platinocyanide was the primary chemical ingredient of pastiiles, which were

developed by several investigators. After irradiation, this material was found

to change from its normal green color to orange, and then to various shades

of brown. (3)

The main difficulty encountered with pastilles was that the color reverted to

its original green on exposure to light, further more, the color standards in

the comparator charts gradually faded and thereby contributed to in accurate

measurements. Most important, these systems were highly energy dependent

because they used materials of high atomic number. There fore, changes in

the spectrum of the x-rays caused large variations in doses registered.

A few years Iater, other chemical systems were developed, for example,

Fruend 6 utilized the effect of x-rays on various iodine compounds. A

mixture of iodofonn was found to be sensitive to x- irradiation and was

employed in dosimetry, but the reaction was also produced by head, light

and spontaneous oxidation, and was not proportional to dosage. 3

According to Gruther et al rt i928 chloroform inadiated with x-rays librates

hydrochloric acid in amounts proportional to the Radiation energy absorbed.

Acid formation increased in water saturated chloroform solutions, it was also

found that irradiation of chloroform solutions by the gamma- rays of Radium

resulted in acid evaluation. 3'a

Numerous chemical systems have been described which undergo chemical

changes on exposure to penetrating x- and gamma- Radiations, such as the

t1

-,.......~-

.., ....

......---

.....

......

..' ....

- ....

-

2-1. Introduction:

The first chemical dosimeters were crude systems which changed color on

exposure to the relatively soft x- rays then being used medically. Barium

platinocyanide was the primary chemical ingredient of pastilles, which were

developed by several investigators. After irradiation, this material was found

to change from its normal green color to orange, and then to various shades

of brown. (3)

The main difficulty encountered with pastilles was that the color reverted to

its original green on exposure to light, further more, the color standards in

the comparator charts gradually faded and thereby contributed to in accurate

measurements. Most important, these systems were highly energy dependent

because they used materials of high atomic number. There fore, changes in

the spectrum of the x-rays caused large variations in doses registered.

A few years later, other chemical systems were developed, for example,

Fruend 6 utilized the effect of x-rays on various iodine compounds. A

mixture of iodoform was found to be sensitive to x- irradiation and was

employed in dosimetry, but the reaction was also produced by head, light

and spontaneous oxidation, and was not proportional to dosage. 3

According to Gruther et al in 1928 chloroform irradiated with x-rays librates

hydrochloric acid in amounts proportional to the Radiation energy absorbed.

Acid formation increased in water saturated chloroform solutions, it was also

found that irradiation of chloroform solutions by the gamma- rays of Radium

1 d · 'd 1 . 34resu te In aCl eva uatlOn. '

Numerous chemical systems have been described which undergo chemical

changes on exposure to penetrating x- and gamma- Radiations, such as the

11

^ J i

oxidation of ferrous to ferric ion compounds and other chemical systems'

Nearly all those chemical systems have been developed and used by

individual working in Radiation chemistry' 3

Physical methods, employing ionization in gases, have been used almost

exclusively for determining the dose of the x and ganlma Radiations utilized

in Radiation thereby and in Radiobiological research.

Because of rapid advancements in electronics, physical methods have

dominated the field of dosimetry, and chemical systems remained in disuse

until quite recentlY.3

2-2 Development of chemical dosimetric systems:

Renewed interest in chemical methods of dosimetry came with the advent of

nuclear reactions, atomic weapons' and the experimental use of increasingly

intense Radiation sources such as the betatron, telecobalt, and Van de Graaff

x-ray generators, and the recent emphasis in Radiobiological researches on

the chemical changes produced in cells and tissue fluids by ionizing

Radiations.3

These developments created an urgent need for dosimeters capable of

registering comparatively large doses of high- energy x- and gamma

Radiations, delivered at tremendously high dose rates up to 105r/min,

furthermore, the dosimeters required by the Armed forces for personnel use

must be small, inexpensive, rugged, thermo stable' direct- reading,

reproducible, and within X20% limits of error responsive to either prompt or

residual bomb gamma Radiation exposure under rigorous field conditions'

T2

- ....

--- ....

--- ...

- ""

-""

- .-

- ....

- ...

- ....

- ....

-,.

- .-

--- ...

--

- ....

oxidation of ferrous to ferric ion compounds and other chemical systems.

Nearly all those chemical systems have been developed and used by

individual working in Radiation chemistry. 3

Physical methods, employing ionization in gases, have been used almost

exclusively for determining the dose of the x and gamma Radiations utilized

in Radiation thereby and in Radiobiological research.

Because of rapid advancements in electronics, physical methods have

dominated the field of dosimetry, and chemical systems remained in disuse

until quite recently. 3

2-2 Development of chemical dosimetric systems:

Renewed interest in chemical methods of dosimetry came with the advent of

nuclear reactions, atomic weapons, and the experimental use of increasingly

intense Radiation sources such as the betatron, telecobalt, and Van de Graaff

x-ray generators, and the recent emphasis in Radiobiological researches on

the chemical changes produced in cells and tissue fluids by ionizing

Radiations. 3

These developments created an urgent need for dosimeters capable of

registering comparatively large doses of high- energy x- and gamma

Radiations, delivered at tremendously high dose rates up to 105r/min,

furthermore, the dosimeters required by the Armed forces for personnel use

must be small, inexpensive, rugged, thermo stable, direct- reading,

reproducible, and within ± 20% limits of error responsive to either prompt or

residual bomb gamma Radiation exposure under rigorous field conditions.

12

a-

t--i--t-T-t:t-t-r_t_

Considerable advanced have been made toward the development of chemical

dosimeter systems and practical dosimeters which can register these

relatively large doses of x- and gamma Radiation. Attention has been

redirected to chemical means of dosimetry because the trend in dose

evaluation is towards the measurement of energy absorption, the chemical

changes produced in tissue equivalent materials should be in many ways

preferable to methods employing iontzation in gases. The yields in aqueous

chemical systems, for example, are not greatly influenced by ambient

temperature changes or wide variations in the energy of the beam (0.1 to 1 .2

MeV) and further more, large integral doses can readily be measured with

dosimeters of small size.

The most difficult problem in chemical dosimetry has been to final stable,

reproducible systems, which register integral doses of x- and gamma-

Radiations in the range below lO0Rad.the ferrous-ferric sulfate system

accepted as the best chemical method for measuring x-ray and gamma ray s

in kilorontgen doses at dose rates up to 1000 Rad/min, and meets most of the

requirements of ideal system. An alternative method with sodium benzoate

or benzene has also been developed. It has advantages that the initial

solutions and the product of irradiation can be kept for longer period without

spontaneous decomposition, both these methods are not sufficiently sensitive

to register galnma- Radiation in the lower part of the dose range that is

biologically most interesting (0 to 1000r). Further more, because of gradual

spontaneous oxidation; the ferrous- ferric system is not sufficiently stable to

permit its instrumentation for long term use. 3

The solution of these two mayor problems in chemical dosimetry has been

accomplished by using systems which respond to Radiation by relatively

long- chain mechanism and by developing methods to control the length of

theses chain reactions while preserving adequate sensitivity in the system.

13

-.............._--

............ --

~._-

-.....i---.- _

r=r=~

~

r=[~

r=(--=

r=

Considerable advanced have been made toward the development of chemical

dosimeter systems and practical dosimeters which can register these

relatively large doses of x- and gamma Radiation. Attention has been

redirected to chemical means of dosimetry because the trend in dose

evaluation is towards the measurement of energy absorption, the chemical

changes produced in tissue equivalent materials should be in many ways

preferable to methods employing ionization in gases. The yields in aqueous

chemical systems, for example, are not greatly influenced by ambient

temperature changes or wide variations in the energy of the beam (0.1 to 1.2

MeV) and further more, large integral doses can readily be measured with

dosimeters of small size.

The most difficult problem in chemical dosimetry has been to final stable,

reproducible systems, which register integral doses of x- and gamma­

Radiations in the range below 100Rad.the ferrous-ferric sulfate system

accepted as the best chemical method for measuring x-ray and gamma ray s

in kilorontgen doses at dose rates up to 1000 Rad/min, and meets most of the

requirements of ideal system. An alternative method with sodium benzoate

or benzene has also been developed. It has advantages that the initial

solutions and the product of irradiation can be kept for longer period without

spontaneous decomposition, both these methods are not sufficiently sensitive

to register gamma- Radiation in the lower part of the dose range that is

biologically most interesting (0 to 1000r). Further more, because of gradual

spontaneous oxidation; the ferrous- ferric system is not sufficiently stable to

permit its instrumentation for long term use. 3

The solution of these two mayor problems in chemical dosimetry has been

accomplished by using systems which respond to Radiation by relatively

long- chain mechanism and by developing methods to control the length of

theses chain reactions while preserving adequate sensitivity in the system.

13

2-3. Classification of dosimetrv methods:

There are three ways in which the dose received from a Radiation source

may be determined:

A. Direct:

In this method the energy absorbed is measured as the heat in to which it is

ultimately degraded. Since the method it self elaborate and tedious it is not

used in routine work but only to calibrate more convenient chemical

methods. Calibration is carried out by measuring the rate of change of

temperature with time, in air free water which has reached stationary state,

i.e., no net chemical range. Then the water is replaced by the dosimetric fluid

and the chemical change measured.

A suitable correction must be made for heating of the walls of the container

by electrons which do not enter the solution. This method has the advantage

that it can be applied to wide range of Radiations and is especially useful for

very mixed Radiations such as are obtained from reactors.

B. Semi- direct:

This method dose not involve direct measurement of energy but of some

physical quantity directly related to energy; either the charge-input or the

ionization due to the Radiation.

I-charge-input:

If the number of particles which are completely absorbed is measured then

(numberf s) x (energ,, f particle)Dose rate:

volume or weight in which absorbed

This method is useful for particle beams from accelerators or for B- particles

from external Radiation source. There are however many sources of error.

t4

--.... -.. ..:

.. -

.. -

----

--

-..;

-..;

-...;

--

----.....

2-3. Classification of dosimetry methods:

There are three ways in which the dose received from a Radiation source

may be determined:

A. Direct:

In this method the energy absorbed is measured as the heat in to which it is

ultimately degraded. Since the method it self elaborate and tedious it is not

used in routine work but only to calibrate more convenient chemical

methods. Calibration is carried out by measuring the rate of change of

temperature with time, in air free water which has reached stationary state,

i.e., no net chemical range. Then the water is replaced by the dosimetric fluid

and the chemical change measured.

A suitable correction must be made for heating of the walls of the container

by electrons which do not enter the solution. This method has the advantage

that it can be applied to wide range of Radiations and is especially useful for

very mixed Radiations such as are obtained from reactors.

B. Semi- direct:

This method dose not involve direct measurement of energy but of some

physical quantity directly related to energy; either the charge-input or the

ionization due to the Radiation.

I-charge-input:

If the number of particles which are completely absorbed is measured then

(number/ s) x (energy/particle)Dose rate =

volume or weight in which absorbed

This method is useful for particle beams from accelerators or for B- particles

from external Radiation source. There are however many sources of error,

14

such as back scatter from cell walls, absorption in the windows,

bremsstrahlung current- leakage and beam inhomogeneity.

II- Ionization

The number of ion pair is measured and dose rate : W, number of ion pairs

per unit maSS or volume where "W: mean energy to create an ion- pair in the

substance of interest. "

The disadvantages of this method are:

a- W has often to be assumed and.

b- The results for ionization in the gas phase must be related to those in

the iiquid phase, sine the ionization of liquids can not generally be

measured.

C-Indirect:

Dosimeters of this type all involved measurements of some chemical or

physical effect caused by Radiation and therefore all require calibration by a

method of type A) or B).

r :

1- Physical effects include crystal coloration; include photo-

conductivity and scintillation.

Il-Dosimeters in which a chemical observed are commonly used r

2-4 Requirements of Ideal Chemical Dosimeters:

The ideal dosimeter for measuring high- energy x-ray or gamma ray

Radiations in the dose range between 50 and 5000Y should embody several

essential properties and have certain conditions characteristics; the first

requirement of chemical dosimeter is that the amount of chemical change is

proportional to the dose and independent of the dose rate (r)

15

.. ..:.

• .=

.. ....:

. ....:

. ..;;

- -=

- ..;;

-..:

-~

---

-...;

---

-...;

.. -

such as back scatter from cell walls, absorption in the windows,

bremsstrahlung current-leakage and beam inhomogeneity.

11- Ionization

The number of ion pair is measured and dose rate = Wx number of ion pairs

per unit mass or volume where "W= mean energy to create an ion- pair in the

substance of interest."

The disadvantages of this method are:

a- W has often to be assumed and.

b- The results for ionization in the gas phase must be related to those in

the liquid phase, sine the ionization of liquids can not generally be

measured.

C-Indirect:

Dosimeters of this type all involved measurements of some chemical or

physical effect caused by Radiation and therefore all require calibration by a

method of type A) or B).

1- Physical effects include crystal coloration; include photo­

conductivity and scintillation.

II-Dosimeters in which a chemical observed are commonly used' 1

2-4 Requirements of Ideal Chemical Dosimeters:

The ideal dosimeter for measuring high- energy x-ray or gamma ray

Radiations in the dose range between 50 and 5000Y should embody several

essential properties and have certain conditions characteristics; the first

requirement of chemical dosimeter is that the amount of chemical change is

proportional to the dose and independent of the dose rate,(J)

15

8 - J

Thus if G value Radiation chemical yeld is defined as the number of

molecules of product formed or reagent destroyed per 100 eV of energy from

the ionizing Radiation

n( r \G(X) - " ' " ' (Jn i t : mol . j - '

t

Where 4*) : number of molecules or ions formed or destroyed.

€ : the energy imported to the matter of that system.

G- Value should be independent of dose and dose rate.

It is desirable that G- value should be independent of the temperature of

Radiation, quality of Radiation and the presence of air and the chemical

impurities, also the chemical changes should be readily measurable (Note.'

1000 Rad of gamma- rays will produce concentration change of 1 '01 G x 1 0-6

mol/L in a reaction in water for which the G-value is G. In addition to, the

dosimeter should be made form biological tissue equivalent materials in

respect to its density and Radiation absorption properties , should lend it self

to standard production method and have suffrcient stability to give shelf life

of at least one year prior to use, thereby permitting the manufacture of

accurate, highly reproducible dosimeters system. Finally the chemical

dosimeter should be easy to prepare and use.

Not a single dosimeter meets all the above mentioned requirements.

However, we can always select one which satisfied maximum requirements

and has known dependence of on the parameters like (LET) Liner Energy

Transfer, dose rate, temperature, etc.

2-5. Types of Chemical SYstems:

Determination of Ra<liation induced changes in gases by chemical analysis is

difficult technically, thus rendering such systems unsuitable for practical

L6

, J ;

L r i

q - j

-' -l

""'!~.......~........--=~========~~=======------~-------

• --=

... ...:

---

-----'---

•. -.-;

Thus if G value Radiation chemical yield is defined as the number of

molecules of product formed or reagent destroyed per 100 eV of energy from

the ionizing Radiation

O(X) n(x) TT . I .-\=--unzt : mo .}&

Where r(x) = number of molecules or ions formed or destroyed.

G = the energy imported to the matter of that system.

G- Value should be independent of dose and dose rate.

It is desirable that G- value should be independent of the temperature of

Radiation, quality of Radiation and the presence of air and the chemical

impurities, also the chemical changes should be readily measurable (Note:

1000 Rad of gamma- rays will produce concentration change of 1.01 G x 10-6

mollL in a reaction in water for which the G-value is G. In addition to, the

dosimeter should be made form biological tissue equivalent materials in

respect to its density and Radiation absorption properties, should lend it self

to standard production method and have sufficient stability to give shelf life

of at least one year prior to use, thereby permitting the manufacture of

accurate, highly reproducible dosimeters system. Finally the chemical

dosimeter should be easy to prepare and use.

Not a single dosimeter meets all the above mentioned requirements.

However, we can always select one which satisfied maximum requirements

and has known dependence of on the parameters like (LET) Liner Energy

Transfer, dose rate, temperature, etc.

2-5. Types of Chemical Systems:

Determination of Radiation induced changes in gases by chemical analysis is

difficult technically, thus rendering such systems unsuitable for practical

16

l- _:

a . l

-\_

+ _

-\-

chemical dosimetry. Solid systems generally are too insensitive to provide

direct- reading methods of dosimetry of value in Radiation biology or

Radiation thereby, unless the changes included in them are detected by

complicated electronic amplifying devices.

Emphasis is being placed on liquid systems for several reasons. They may be

prepared from reagents which are water- or tissue equivalent in respect to

density and Radiation absorption properties. The Radiation induces reaction

products are relatively stable and can be measured directly by color changes,

or indirectly by simple analyical procedures. Liquid chemical dosimeters

can be prepared in small containers within body cavity, in tumor areas, or at

positions close to high, Intensity sources. Finally aqueous chemical systems

absorb Radiation of various type and energies by mechanisms more like

those occurring in body tissues or fluid than do gaseous or solid systems.

2-6. Liquid aqueous systems :

Principle: In a dosirneter of this type, solute is present which can reacts

stochiometrically with one or more of the primary species whilst in

sufficiently low concentration so as not to influence the rate of energy

deposition.

To understand the mode of action of aqueous dosimeters it is necessary first

to consider the nature and distribution of the species. These differ some what

for Radiations of high and low linear Energy Transfer (LET).

Immediately after the passage of through water of a fast charged particle

those molecules closed to the Radiation track are ionized whilst those further

away are raised to an excited level.

H2O -+ HzO- * e- f HzO*

_ t !

t *

\

t -I

1 1I I

_...:.

..~'..::::

-. ..:.

-~

.. ...:

~.

.. ...:

.....:

..... ...:

--.......

chemical dosimetry. Solid systems generally are too insensitive to provide

direct- reading methods of dosimetry of value in Radiation biology or

Radiation thereby, unless the changes included in them are detected by

complicated electronic amplifying devices.

Emphasis is being placed on liquid systems for several reasons. They may be

prepared from reagents which are water- or tissue equivalent in respect to

density and Radiation absorption properties. The Radiation induces reaction

products are relatively stable and can be measured directly by color changes,

or indirectly by simple analytical procedures. Liquid chemical dosimeters

can be prepared in small containers within body cavity, in tumor areas, or at

positions close to high, Intensity sources. Finally aqueous chemical systems

absorb Radiation of various type and energies by mechanisms more like

those occurring in body tissues or fluid than do gaseous or solid systems.

2-6. Liquid aqueous systems:

Principle: In a dosimeter of this type, solute is present which can reacts

stochiometrically with one or more of the primary species whilst in

sufficiently low concentration so as not to influence the rate of energy

deposition.

To understand the mode of action of aqueous dosimeters it is necessary first

to consider the nature and distribution of the species. These differ some what

for Radiations of high and low linear Energy Transfer (LET).

Immediately after the passage of through water of a fast charged particle

those molecules closed to the Radiation track are ionized whilst those further

away are raised to an excited level.

17

b. -:

\

! , . J

\ ,

I ' :

\-

The Hzo- ion reacts with H2o to give oH' Radicals whilst H2o* may

decompose or be deactivated, all within 1O-ttg. Formerly, it was considered

that the electron reacted rapidly to form a hydrogen atom and a hydroxide

ion, but it is now known that the electron persists up to about 10-as before

reacting in this way. After not less than 10-'1s the electron becomes solvated

by the water molecules and in these conditions is usually represented by

e a 9

H:O* + HzO -+ H2O* + OHo

H2O* -+ Ho + OHo

In the period i0-lrs to 10-7s there is competition between combination of

Radicals to give "molecular products" and diffusive escape from the spur or

track. The recombination reactions Ho * OHo-+ HzO, or e- + OHo -> OH

are omitted because they lead to no chemical change in a solute, combination

reactions are:

e-uo *e uo ---+ H2 + 2OH-

Ho + Ho _-+ H2

e-ro+ Hu--- H: + OH-

OHo + OHo --' H:Oz

Radiation of high LET favors the formation of molecular products over

diffusive escape and also the intra -track reactions:

OHo+ H2O2* H2O+ H2O

e-uq* HzOz-- OH-+ OHo

Since most of the "molecular products" have been produced after the lapse of

10-r7s the Radical combination process will not be interfered with by solutes

which can react with e- or OH or both, provided the half-lives of these latter

reactions are larger than about l0-7s. These half-lives vary with nature and

g :

^.

u t :

--_t-_

w :

\

u :

3/ ,:

t :

I

'!r r -:

lcr :

lr, .:

\ . . :

L, .:

t , :

t.r-t . j

t,-"r:t:t:

18

E .

... .:..

.. ~

.. ...:.

-~

... ..:

--~

~, -

_....a..­1

r[~

[-~

. ..::

[~

[-~

, ..,

L

The H20+ ion reacts with H20 to give OHO Radicals whilst H20* may

decompose or be deactivated, all within 10-12g. Formerly, it was considered

that the electron reacted rapidly to form a hydrogen atom and a hydroxide

ion, but it is now known that the electron persists up to about 10-4s before

reacting in this way. After not less than 10-IIS the electron becomes solvated

by the water molecules and in these conditions is usually represented by

e aq

H20+ + H20 ~ H20+ + OHo

H20* ~ HO + OHo

In the period 10-1JS to 10-7s there is competition between combination of

Radicals to give "molecular products" and diffusive escape from the spur or

track. The recombination reactions HO + OHo~ H20, or e- + OHo ~ OH­

are omitted because they lead to no chemical change in a solute, combination

reactions are:

OHO + OHo ~ H20 2

Radiation of high LET favors the formation of molecular products over

diffusive escape and also the intra -track reactions:

OHo+ H20 r -+ H20+ H20

e-aq+ H202~ OH-+ OHo

Since most ofthe "molecular products" have been produced after the lapse of

10-17s the Radical combination process will not be interfered with by solutes

which can react with e- or OH or both, provided the half-lives of these latter

reactions are larger than about 10-7s. These half-lives vary with nature and

18

J

concentration of solute but frequently the rate constant of the bimolecular

reaction of reactive solutes with these Radicals is about 1010M-rs-t so that, if

- l 0 - r0l0_ , (

^ , (= l0_ ,sso lute '

The G vaiue of the primary species may be treated as being sensibly

constant. The time scale of these processes is illustrated in table (2).

Therefore, we usually write the following reactions fin stochiometry

equations G "H") is commonly written for G (e ) + G (H) because H and e-uo

are frequently stochiometrically equivalents. 1

2-7. Prerequisites of chemical dosimetry:

Radiolytic reactions are extremely sensitive to trace impurities. Hence

water, glassware's and inadiation cells used for dosimetry must be free from

trace of amount of organic and inorganic impurities 2

T9

Table (2): Events in the radiolysis of aqueous solutions

Time(s)Events in the aqueous solutions

-10 - ' Ionization and excitation. HrO_+HrO-+ s- + H,O".4 x10 - ' Formation of the hydroxyl Radical; HzO- + HzO-+HzO- + OH.- 10 - ' ' Dissociation of H"O" ---+ H+OH.-10 - " Solvation of the electron: e ---+ e- 10-''/trr Relaxation time of the ion- atmosphere of e- aq in an aqueous solution of

ionic strength:p-10 - ' Combination; (2e- ae r Hz + 2OH'; euo-* H-+ H2 and 2OH -- H2O2). And

Reactions (e-uo*OH---+OH-andH+OH--HzO) .reactions virtually completein low LET systems. Intra lack reactions (OH+ H2O2---+ HzO + H2O and e-uo+ HzOz ---OH+ OH-). In high LET systems will also be complete in aboutthis time.

-10- '" / [s] Time in which 50oh of Radicals will have reacted with reactive solute Spresent in concentration IS].

concentration of solute but frequently the rate constant of the bimolecular

reaction of reactive solutes with these Radicals is about 1OloM-lS-l so that, if

10-10

10-7( (>::::, 10-5ssolute

The G value of the pnmary speCIes may be treated as being sensibly

constant. The time scale of these processes is illustrated in table (2).

Therefore, we usually write the following reactions [in stochiometry

..:: equations G "H") is commonly written for G (e-) + G (H) because Hand e-aq

are frequently stochiometrically equivalents. 1

Table (2): Events in the radiolysis of aqueous solutions

Events in the aqueous solutionsTime(s)

~1O- Ionization and excitation, H20~H20++ e- + H2O°.4 xlO-1

'> Formation of the hydroxyl Radical; H20' + H20~H20 +OH.~lO-u Dissociation of Ho0° ~ H+OH.~10-11 Solvation of the electron; e- ~ e- aa.~lO-lU/1l Relaxation time of the ion- atmosphere of e- aq in an aqueous solution of

ionic strength=1l~1O-/ Combination; (2e- aq ~ H2 + 20K; eaq-+ H~ H2 and 20H ~ H20 2). And

Reactions (e-aq+OH~OH-andH+OH~H20) .reactions virtually completein low LET systems. Intra lack reactions (OH+ H202~ H20 + H20 and e-aq+ H20 2~OH+ OH} In high LET systems will also be complete in aboutthis time.

~lO-lU/[S] Time in which 50% of Radicals will have reacted with reactive solute Spresent in concentration [S].

2-7. Prerequisites of chemical dosimetry:

Radiolytic reactions are extremely sensitive to trace impurities. Hence

water, glassware's and irradiation cells used for dosimetry must be free from

trace of amount of organic and inorganic impurities 2

19

l -

II

t _

2-7-1. Purification of water:

Commercially available distilled water contains traces of organic and

inorganic impurities which have been shown to cause significant variations

in the response of these systems. Pure water is necessary for reproducible

results. Distilled water is purified by redistillation from alkaline

pennanganate and from sulfuric acid followed by a third redistillation and by

collection of the condensed steam into closed Pyrex glass containers. This

procedure gives a supply of water of low conductivity which is sufficiently

free of all impurities. This pure water is used in the preparation of other

reagents and for final rinsing of all glass ware.

2-7-2 Treatment of glass wares and irradiation cells:

Glass wares and irradiation cells used for dosimetry arc generally made from

Borosilicate or Silica glass, they are filled with or dipped in 1:1 mixture of

concentrated sulphuric and nitric acids for 24 hours, then washed

successively with tap water and distilled water. Then they are filled distiiled

water and exposed to a dose of approximately lKGy.

Inadiation cells purified in this way are kept filled with distilled water or

with dosimetric solution. when not in use. '

2-7-3. Treatment of plastic irradiation cells:

Use of material like Teflon, Perspex, ploy ethylene, ploy styrene and poly

propylene as container for a chemical dosimeter require a special procedure

for cleaning, storage and use. The inner walls of the inadiation tube should

be inert. i.e. it should not liberate any impurities during irradiation or pre and

post irradiation storage of dosimetric solution. The procedure followed as

follows:

20

..

... -

...

...

... -

... -

.... -

--

--

..... -

-. -

- -

--

L~

2-7-1. Purification of water:

Commercially available distilled water contains traces of orgamc and

inorganic impurities which have been shown to cause significant variations

in the response of these systems. Pure water is necessary for reproducible

results. Distilled water is purified by redistillation from alkaline

permanganate and from sulfuric acid followed by a third redistillation and by

collection of the condensed steam into closed Pyrex glass containers. This

procedure gives a supply of water of low conductivity which is sufficiently

free of all impurities. This pure water is used in the preparation of other

reagents and for final rinsing of all glass ware.

2-7-2 Treatment of glass wares and irradiation cells:

Glass wares and irradiation cells used for dosimetry are generally made from

Borosilicate or Silica glass, they are filled with or dipped in 1: 1 mixture of

concentrated sulphuric and nitric acids for 24 hours, then washed

successively with tap water and distilled water. Then they are filled distilled

water and exposed to a dose of approximately lKGy.

Irradiation cells purified in this way are kept filled with distilled water or

with dosimetric solution, when not in use. 2

2-7-3. Treatment of plastic irradiation cells:

Use of material like Teflon, Perspex, ploy ethylene, ploy styrene and poly

propylene as container for a chemical dosimeter require a special procedure

for cleaning, storage and use. The inner walls of the irradiation tube should

be inert. i.e. it should not liberate any impurities during irradiation or pre and

post irradiation storage of dosimetric solution. The procedure followed as

follows:

20

E-I

l r -

!

! F

I

r i -II

\-

! , - -

L

- -

I -

- _

t -

- -

l -

b s

t

\ - -

l -

t

Clcaning: Plast ic tubes afc f i l lecl u, i th l0% I INIOT I 'or 24 hours. - fhen

they arc l inscc l w i th tap watc r i lnc l then c l i s t i l l ec l rva tc r ' . ' l ' o rna l<c the tubc

free fi 'otr any fr,rrther clctachable irrpLrrity lronr the inner lvall, the tLrbes

are f i l lecl wi th c losimetr ic soh-r t ion ancl exposecl to a c lose ol ' .10 Gy.

Storagc. 'Plast ic t t rbes or bags are I l l lcc l r . r , i th c losimctr ic solut iorr n,hcrr

not ir-r use.

2-7-4. IJse of i r rad ia t ion cc l ls :

When glass or plast ic i rracl iat iorr cel ls are to be usecl fbr dosirnetry. thc

o ld dos imctr ic so lu t ion in thern is c l iscarc lec l . ' fhe ce l is are r insed at least

two times with liesl-r closirnetric solution. I-hey are then ll l led rvith tht:

solut ion, stopper arrcl i rracl iatecl. 2

2-8 . S tab i l i z ing Age n ts :

Al l mater i i i ls shor,r lc l bc reagent gracle or analyt ical ly pr-rre substances, so

statecl by the tnanulactr , r ret ' . I rur thcr pr-rr i l rcat ion is nracle Lry l t 'ac: t ic lnal

rec l i s t i i l a t ion anc l /o r by rcc rys ta l l i za t ion . A l l reagents shoLr lc l be l i cp t in

clean, c losecl , I )yrex containers. ' I 'he rcagcrr t rvhich have been l 'ouncl tcr

provide aclequate thernral stabi l i ty ancl s iurul taneously to rc i tc lcr '

chloro{bnn ancl / or tetrachloroethylene- c lye systc.nr lbr exanrple relat ivcl) '

c lose- rate ancl ternperature inciepenclent. l

2 -9 Daf in i t ion o f C va luc :

G va lue l {ac l ia t ion chcnr ica l y ic ld i s thc l ' L rnc l ln rcn la l quunt i t r t i vc

character ist ic o{ ' l {acl iat ion inclr-rce c l re act ion in a chcmical c losin-re ler . The

react ior-r chernical y ie lc l , G 1. ; o l 'an ent i ty, x, is the c1r-rot ient of 'n(X) b1'r ,

where n(x) is t l ' ie mean amolrnt of sr-rbstance of that ent i ty proclucecl ,

destroyed or changed in s1,stem b1, t l ie eticrgl, inrpartecl,

t-

rt"-t_r-r

2I

~­

i...--

-c

-~

-.

----~--

.. -

.. -

.. -

il.. -

l -

-L-

r=r=c[~

['-

Cleaning: Plastic tubes are filled with 10% HN03 for 24 hours. Then

they are rinsed with tap water and then distilled water. 'ro make the tube

free from any further detachable impurity from the inner wall, the tubes

are filled with dosimetric solution and exposed to a dose of 40 Gy.

Storage: Plastic tubes or bags are filled with dosimetric solution when

not in use.

2-7-4. Use of irradiation cells:

When glass or plastic irradiation cells are to be used for dosimetry, the

old dosimetric solution in them is discarded. The cells are rinsed at least

two times with fresh dosimetric solution. They are then filled with the

solution, stopper and irradiated. 2

2-8. Stabilizing Agents:

All materials should be reagent grade or analytically pure substances, so

stated by the manufacturer. Further purification is made by fractional

redistillation and/or by recrystallization. All reagents should be kept in

clean, dosed, Pyrex containers. The reagent which have been found to

provide adequate thermal stability and simultaneously to render

chloroform and/ or tetrachloroethylene- dye system for example relatively

dose- rate and temperature independent. 3

2-9 Definition of G value:

G value Radiation chemical yield is the fundamental quantitative

characteristic of Radiation induced reaction in a chemical dosimeter. The

reaction chemical yield, G (x) of an entity, x, is the quotient of n(X) by;"

where n(x) is the mean amount of substance of that entity produced,

destroyed or changed in system by the energy imparted,

21

t['L , .

J

l E .

^L

-A

l L l -II

-A

j-r-

l - -

-L

l -

L

\ -

JIL , -

ll

I\ _

_t.-

I*

,A-

i\*

l-

I^^

L .

e , t o the t l l a t t e l . o f ' t ha t sys te ln , t hus :

G(X) = n(x) f r : (Jn i t : n to l , /

O r i t i s c le f i nec l as thc r t L r t r t be l o l ' i ons , 1 r ' cc I {a r l i ca l s , u ton rs , r . } r ( ) l c r ru l cs

fbrrned or c l isapPearec l \vhcn thc syst .enr has absor-bcc l 100 ev,o l -e .e l .g '

f t "orn the ion iz ing rac l ia t ion 2 .

22

~ -

~ -

... -

.. -

L

L

,-

E, to the matter of that systcm, thus:

G( X) = n(x)/dJnir : mol.! I

Or it is defined as the number of ions, frcc R~ldic~J!s, ~ltoms; molecules

formed or disappeared when the system has ~lbsorbcd 100 ev of energy

from the ionizing radiation 2 .

22

l -

-t.l.aI

t . -

1-

l _

-I

l -

1-

l _

.t-

l -

THAPTERTHREE)- 3. TYPES OF AQUEOUS CHEMICAL DOSIMETERS

l-

t _

\ _

! -

l . '

A-

.. -

l _

IHAPTER THREE~ ---L.

l _

l _

l _

.. -

... -

.. -

. -

3- TYPES OF AQUEOUS CHEMICAL DOSIMETERS

-..L.- .

L I

; :

l , r

t r

t ]

3-1. Fricke dosimeter:

This dosimeter "ferrous- ferric sulfate system", which described by Fricke

and Morse then developed by Miller t, is presently accepted by numerous

workers as the best chemical method for measuring x and garnma rays, and it

meets most if the requirements of the ideal system'(3)

This dosimeter is the best one for low medium dose-rate. It is based on the

oxidation of ferrous to ferric ions in aerated 0.8N H2SO4 and the ferric ion

concentration may be measured as follows:-

i) By measuring of light absorption at 3050 A'. The extinction :

(2200t9) M-r at 20'C and show the considerable temperature

dependence, namely @e I e)dT :0.007.

ii) Alternatively the ortho-phenanthroline complex with Fe*2 may be

formed and its light absorption at 5100 A0 measured: -11000 M-lcm-r.

iii) Other techniques involve potentiometric titration, labeling and

measurement of the light absorption of the Fe SCN*2 complexes at

4600 A0.

3-1-1. Principle:

When an air saturated dilute ferrous sulfate or ferrous ammonium sulfate in

solution in 0.8 N H2SO4 is exposed to ionizing Radiation, ferrous ions are

oxidized to ferric ions in a series of quantitative and irreversible reactions

Fe 2* -+ Fe3*

Concentration of ferric ions gives the measure of absorbed dose. The

concentration is measured by spectrophotometric analysis means which is

generally more convenient than chemical titration methods for it is rapid,

l *

;

t--t-_t^tt.r_itii-_i_t+

I

23

l .--

l _

~

~

~

~

r:r:~

~

l~

~;---.

3-1. Fricke dosimeter:

This dosimeter "ferrous- ferric sulfate system", which described by Fricke

and Morse then developed by Miller 5, is presently accepted by numerous

workers as the best chemical method for measuring x and gamma rays, and it

meets most if the requirements of the ideal system-(3)

This dosimeter is the best one for low medium dose-rate. It is based on the

oxidation of ferrous to ferric ions in aerated 0.8N H2S04 and the ferric ion

concentration may be measured as follows:-

i) By measuring of light absorption at 3050 Aa. The extinction

(2200±9) M-J at 20°C and show the considerable temperature

dependence, namely (dEI E)dT = 0.007.

ii) Alternatively the ortho-phenanthroline complex with Fe+2 may be

formed and its light absorption at 5100 Aa measured: ~11000 M-Jcm- I.

iii) Other techniques involve potentiometric titration, labeling and

measurement of the light absorption of the Fe SCN+2 complexes at

4600 Aa.

3-1-1. Principle:

When an air saturated dilute ferrous sulfate or ferrous ammonium sulfate in

solution in 0.8 N H2S04 is exposed to ionizing Radiation, ferrous ions are

oxidized to ferric ions in a series of quantitative and irreversible reactions

Fe 2+ -+ Fe3+

Concentration of ferric ions gives the measure of absorbed dose. The

concentration is measured by spectrophotometric analysis means which is

generally more convenient than chemical titration methods for it is rapid,

23

t *

L !

i. _-

l q

L !

II

l . !

acQurate, and expedient for the analysis for low ferric concentration andsmall quantities of solution.(1)

3-l-Z Basic reactions:

s -uc+Huq-Ho (3 l )

In 0'8N HzSo+, this reaction is complete in less than 10-es. In deaeratedsolution at pH<1 and in the absence of organic impurities the onlyparticipating reactions are:

H+ Fe2* *HzO - Hz*oH +Fe3* (3.2)

oH'+ Fe 2* __- oH-+ Fe3* (3 3)

H2O'+ Fe2n --- OH + OH- + Fe3* (3.4)

HO2+Fe2* * Hoz-* Fe3* (3.5)

Hence for time (t) : co

G 1r'":*y- : Gs *Gon -t2Gnzoz*3G'oz.

G 1u zy: GHz*Gn

Reaction ( a ) is slow compared with the others when t: 0G 1. . ' * )o:Gu * Gou* G noz

In practice the half -life of reaction (3.a) may be increased by using verydilute soiutions of ferrous sulphate and thus G 1re+:)0 measured. In an aeratedsolution reaction (3.2) is completely superseded by reaction (3.6) followedby reaction (3.5)

U + Oz -) HOz (3.6)

Hence:

G 1n. :*;- : 3Gn +Gos+3Gnozt2GHzOz

c (Hz) :G (Hz)

G 1E.:*; o :GH*Gon*Gsoz

3-1-3. Calculation of the absorbed dose..

t:It-tlt-fIIt.it_r-L *

[ _

-! *

I

24

l .!!

accurate, and expedient for the analysis for low ferric concentration andsmall quantities of solution. (l)

3-1-2 Basic reactions:

- - 0e aq+ H aq ~ H (3.1 )

Hence:

G (Fe3+) 0=GH+GOH+GH023-1-3. Calculation of the absorbed dose:

G (Fe 3+)00 = 3GH+GoH+3GH02+2GH202

G (H2) =G (H2)

(3.2)

(3.3)

(3.4)

(3.5)

H+ Fe2++H20 ---+ H2+OH-+Fe3+

OHo+ Fe 2+ ~ OH-+ Fe3+

H20 2+ Fe2+~ OHo+ OH- + Fe3+

H02+Fe2+ ---+ H02-+ Fe3+

G (Fe 3+)00 = GH+GOH +2GH202+3GH02,

G (H 2) = GH2+GH

Reaction ( & ) is slow compared with the others when t= 0

G (Fe 3+)0 =GH+ GOH + G H02

In practice the half -life of reaction (3.4) may be increased by using verydilute solutions of ferrous sulphate and thus G (Fe+3)0 measured. In an aeratedsolution reaction (3.2) is completely superseded by reaction (3.6) followedby reaction (3.5)

Hence for time (t) = (fJ

In 0.8N H2S04 , this reaction is complete in less than 10-9s. In deaeratedsolution at pH<l and in the absence of organic impurities the onlyparticipating reactions are:

r----

l A

r~

~

~

~

LLr[

[

[

rr

24

GyM

-,

--

l-

I

I

!

I - -

L-

!

!

Ferric ion has two absorption peaks at 3004 nm and 224 nm, the one at 224

nm being more intense, the sensitivity of this analyical method can be

doubled by measuring the optical unit density at 224 nm ferric ion peak.

Another advantage of measuring at 224 nm peak is that the molar linear

absorption coefficient increase with rising temperature by only 0.13% C.

However, at this lower wavelength, the absorption due to ferrous is not

whol ly negl ig ib le.

In addition, impurities from plastic container are reported to be more

troublesome at 224nm. Hence 304nm is used for measurement of Fe*3 ion

concentration, at temperature 25 oC.

Molar absorption coefficient should be determined by measuring of optical

density of solutions of different known concentrations of ferric ions.

Absorbance of irradiated dosimeters is measured against the Inadiated

solution form the standard flask, optical density of the unirradiated reference

blanks in the dosimetric tubes is also measured against solution in standard

flask. Absorbance of the irradiated solution is corrected for reference blank

reading. The absorbed dose is calculated from the following equation 2:

D_Pe I Gu,

Where:

M

€

I

: the difference in absorbance (optical

irradiated and unirradiated solution.

: molar linear absorption coefficient.

: optical path length 0.01 m

density) between the

p : density of solution: 1024 Kg m3

G(' , : G 10.* ' ) : 1 .61 x 10-6 mol J- l .

Substituting the above values gives:

25

-

"

J-

Ferric ion has two absorption peaks at 3004 nm and 224 nm, the one at 224

nm being more intense, the sensitivity of this analytical method can be

doubled by measuring the optical unit density at 224 nm ferric ion peak.

Another advantage of measuring at 224 nm peak is that the molar linear

absorption coefficient increase with rising temperature by only 0.13% C.

However, at this lower wavelength, the absorption due to ferrous is not

wholly negligible.

In addition, impurities from plastic container are reported to be more

troublesome at 224nm. Hence 304nm is used for measurement of Fe+3 ion

concentration, at temperature 25°C.

Molar absorption coefficient should be determined by measuring of optical

density of solutions of different known concentrations of ferric ions.

Absorbance of irradiated dosimeters is measured against the Irradiated

solution form the standard flask, optical density of the unirradiated reference

blanks in the dosimetric tubes is also measured against solution in standard

flask. Absorbance of the irradiated solution is corrected for reference blank

reading. The absorbed dose is calculated from the following equation 2:

D= M GyP& I G(x)

Where:

M = the difference in absorbance (optical density) between the

irradiated and unirradiated solution.

& = molar linear absorption coefficient.

= optical path length 0.01 m

p = density of solution= 1024 Kg m-3

G(x) = G(F/3) = 1.61 x10-6 mol r l

.

Substituting the above values gives:

25

rb,-

--

{

\a-

a-

\

L-

\,

\,

I

I

L

tt

L

n _ 0.0977 LA_ _

G lFe'* lx e\ / o t 2 5 " C

3-l-4. Influence of various factors :

I) Oxygen Supply:

It is necessary that the Fricke dosimeter should have an adequate supply ofoxygen since, when all the oxygen has been used up H can no longer formH2o and G (Fe*3)is conespondingly diminished, when oxygen is completelyexhausted ,reaction mechanism change reducing G(Fe ,*) to 0.g5 Mol J-.

Fe 2* +H" + H* -+ Fe3* + 11,

Here one atom oxidizes only one ferrous ion to ferric instead of three.Therefore, G (Fe*3) :2 GH26,* esFr

II) Ferrous ion concentration:

For concentration of ferrous ion < l0-1 M reaction (3.4) becomes slow inrelation to irradiation time, so that if the analyical procedures are rapid themeasured G (Fe*3) witl lie between G (Fen3)6and G (F"*r)_. Solutions of thisconcentration are also inconvenient in that all the ferrous ion will be destrovby a dose of 7000 Rad. (r)

III) Sulphuric acid concentration:

The concentration of 0.4M is always used; chemically all that is necessarv isthat the pH of the solution shall be less than 1.5.

L

26

w

...

-----

\...

t.

D = O.0977MG (Fe 3

+ )X £ at 2SoC

3-1-4. Influence of various factors:

I) Oxygen Supply:

It is necessary that the Fricke dosimeter should have an adequate supply ofoxygen since, when all the oxygen has been used up H can no longer formH20 and G (Fe+3)is correspondingly diminished, when oxygen is completelyexhausted ,reaction mechanism change reducing G(Fe 3+) to 0.85 Mol f.

Fe 2+ +HO

+ H+ --...., Fe3++ H2Here one atom oxidizes only one ferrous ion to ferric instead of three.

Therefore, G (Fe+3) = 2 GH202+ GOH

11) Ferrous ion concentration:

For concentration of ferrous ion < 10-4 M reaction (3.4) becomes slow inrelation to irradiation time, so that if the analytical procedures are rapid themeasured G (Fe+3) will lie between G (Fe+3)oand G (Fe+3}Xl. Solutions of thisconcentration are also inconvenient in that all the ferrous ion will be destroyby a dose of 7000 Rad. (1)

Ill) Sulphuric acid concentration:

The concentration of O.4M is always used; chemically all that is necessary isthat the pH of the solution shall be less than 1.5.

26

-

-.L

rI

-,4-

-L

-.4-

-./-

-.4-

-,/-

0.4 M sulphuric acid solution is used because Fricke consider that the

electron concentration of this medium would approximate to that of the

living cell.

IV) Purity of reagents and cleanliness of glass ware:

Organic substances, RH, compete with ferrous for OH Radicals

OHo+ B11 - HzO + Ro

And the resultant organic Radical, Ro, may either react with 02 to give Ro2'

which oxidizes three ferrous ions, so that G (Fe'*) increases.

Ro + Oz- ROzo

e .g. RH: alcohol.

RO2o+Fe 2* -) Fe3* +ROz-

ROOH+ Fe2' -+ pe3+ +ROO+OH-

ROo + Fe 2* -+ Fe 3* +RO--+ ROH

or reduce Fe3n when G 1Fe3n)- decreases. The former predominates when

RH is alcohol and the latter when RH is allyl thiourea, or styrene.

A test of organic impurities can be made by adding chloride ion (-10 3- M

NaCl) when the rapid reaction:

OH" +Cl -+OH- +Clo

occur, since chloride atoms react much more rapidly with Fe2* than RH, any

change of G(Fe3*) caused by addition of chloride is indicative of the

presence of organic impurity. Great care is necessary to ensure that pure

water and pure chemicals reagents are used in very clean glass containers 1

V) Effect of Dose- rate:

Irrrrr

27

• L

• L

· "

· .

.. 1

0.4 M sulphuric acid solution is used because Fricke consider that the

electron concentration of this medium would approximate to that of the

living cell.

IV) Purity of reagents and cleanliness of glass ware:

Organic substances, RH, compete with ferrous for OH Radicals

OHO+ RH ~ H20 + RO

And the resultant organic Radical, RO, may either react with O2 to give R02°

which oxidizes three ferrous ions, so that G (Fe3+) increases.

RO '+ 02~ R02°

e.g. RH = alcohol.

R02o+Fe 2+ ~ Fe3++R02-

ROOH+ Fe2+ ~ Fe3++ROo+OH-

RO° + Fe 2+ ~ Fe 3+ +RO-~ ROH

Or reduce Fe3+ when G (Fe3+)oo decreases. The former predominates when

RH is alcohol and the latter when RH is allyl thiourea, or styrene.

A test of organic impurities can be made by adding chloride ion (~l 0 3- M

NaCl) when the rapid reaction:

OHO +Cl -~OH- +Clo

Occur, since chloride atoms react much more rapidly with Fe2+than RH, any

change of G(Fe3+) caused by addition of chloride is indicative of the

presence of organic impurity. Great care is necessary to ensure that pure

water and pure chemicals reagents are used in very clean glass containers 1

V) Effect of Dose- rate:

27

At dose-rate of about 108 Rad,4nin Radicals from adjacent tract with the

solute and as consequence G (Fe'*) diminishes as the dose-rate is further

increased. Practical

a. High LET, e.g. Po particle - up to 1020 e v 1-1 S-r

b. Low LET, e.g. X- or r- rays- up to 1026 e v 1-r S I

VI) Effect of linear Energy Transfer (L.E.T):

From the mechanism of energy loss one would be expect no great difference

in the number of e-uo , Ho and OHo produced by ionizing particles per 100

eV, as either phase or particle is changed. However, as the LET is altered by

changing the energy or mass of the particle or by changing from water vapor

to liquid, also the true G-s26 is constant the fraction of e-,q, Ho and OHo

escaping will vary between limits of 100% and 0o/o it is equivalent to saylng

that the molecular product yields increase, tending to 112 G-Hzo whilst Gg

and G6s decrease to zero it follows that G 1F*3; will decrease as LET

increase.

VII) Temperature:

By increasing temperature during irradiation G(F*') increase slightly The

temperature at which the spectrophotometric measurements are dose is very

important as the molar linear absorption coefficient increase by about 0.69%

per C for the 304 nm peak. For this reason it is important to know the

temperature at which the spechrophotometric measurements are done.

3-2 Ceric Sulphate (Ceric- Cerous) dosimeter.'

This dosimeter makes use of the reduction of ceric sulphate of by Radiation.

This dosimeter is standardtzed against Fricke dosimeter. With great care

precision of + lo/o can be obtained. (1)

28

At dose-rate of about 108 Rad linin Radicals from adjacent tract with the

solute and as consequence G (Fe3+) diminishes as the dose-rate is further

increased. Practical

a. High LET, e.g. Po particle - up to 1020 e v 1-1 S-l

b. Low LET, e.g. X- or r- rays- up to 1026 e v 1-1 S-l

VI) Effect of linear Energy Transfer (L.E.T):

From the mechanism of energy loss one would be expect no great difference

in the number of e-aq , HO and GHO produced by ionizing particles per 100

eV, as either phase or particle is changed. However, as the LET is altered by

changing the energy or mass of the particle or by changing from water vapor

to liquid, also the true G-H20 is constant the fraction of e-aq , HO and GHO

escaping will vary between limits of 100% and 0% it is equivalent to saying

that the molecular product yields increase, tending to 1/2 G-H20 whilst GH

and GOH decrease to zero it follows that G (F+3) will decrease as LET

mcrease.

VII) Temperature:

By increasing temperature during irradiation G(F+3) increase slightly The

temperature at which the spectrophotometric measurements are dose is very

important as the molar linear absorption coefficient increase by about 0.69%

per C for the 304 nm peak. For this reason it is important to know the

temperature at which the spechrophotometric measurements are done.

3-2 Ceric Sulphate (Ceric- Cerous) dosimeter:

This dosimeter makes use of the reduction of ceric sulphate of by Radiation.

This dosimeter is standardized against Fricke dosimeter. With great care

precision of± 1% can be obtained. (1)

28

3-2-l Principle:

when dilute aerated solution of ceric sulphate in 0.gN H2so4 is exposed to

ionizing Radiation, ceric ions are reduced to cerous. Decrease in ceric ions

concentration is measured spectrophotometrically to evaluate the absorbed

dose.

Ce4* ---) Ce3*

The basic reactions dosimeters are about + 3oA. Are dosimeters is about +

3%.

H (or HO2) + Ce ---) H*(or ,1n + Oz) * Ce3* (3.7)

H2o, + Cea* ----) H*+ Ho2 + Ce3* (3.g)

OH * Ce3* -) OH- + ge4* (3.9)

G (Ce3*) = GH + 2GH2O2_ GOH_ (3. 10)

The yield of Ce is independent of oxygen since H hand H2o both reduce

ceric ions, the stoichiometry equations indicates that G(ce) is largelydetermined by the magnitude of 4 Gn:oz- 2Gnzand is therefore:

a. Strongly dependent on LET

b' Small and consequently very useful for measurement of hieh dose-rate.

3-2-2 Calculation of absorbed dose:

when the dosimeter is used for calibration pu{pose, spectrophotometry isused to measure the decrease in ceric ion concentration .as the starting Ce*3

ion concentration is high, both unirradiated and irradiated solutions have to

be diluted to obey Beer Lambert's law .ceric ions have an absorption

maximum at 320nm .the molar linear absorption coefficient e (ce*1) is

561mzmo1-Iat 25c0 e (ce*a) at this wavelength is only 0.27m2 mol-r.so

interference to cerous ions can be neglected.

The absorbed dose is then calculated as follows 2:

29

3-2-1 Principle:

When dilute aerated solution of ceric sulphate in 0.8N H2S04 is exposed to

ionizing Radiation, ceric ions are reduced to cerous. Decrease in ceric ions

concentration is measured spectrophotometrically to evaluate the absorbed

dose.

C 4+ C 3+e ---+ e

The basic reactions dosimeters are about ± 3%. Are dosimeters is about ±

3%.

H (or H02) + Ce ---+ H+(or H+ + O2) + Ce3+ (3.7)

H20 2 + Ce 4+ ---+ H++ H02 + Ce3+ (3.8)

OH + Ce3+ ~ OH- + Ce4+ (3.9)

G (Ce3+) = GH + 2GH20 2 - GOH- (3.10)

The yield of Ce is independent of oxygen since H hand H20 both reduce

ceric ions, the stoichiometry equations indicates that G(Ce) is largely

determined by the magnitude of 4 GH20r 2GH2 and is therefore:

a. Strongly dependent on LET

b. Small and consequently very useful for measurement of high dose­

rate.

3-2-2 Calculation of absorbed dose:

When the dosimeter is used for calibration purpose, spectrophotometry is

used to measure the decrease in ceric ion concentration .as the starting Ce+3

ion concentration is high, both unirradiated and irradiated solutions have to

be diluted to obey Beer Lambert's law .ceric ions have an absorption

maximum at 320nm .the molar linear absorption coefficient [> (Ce+4) is

56lm2mor lat 25Co[> (Ce+4) at this wavelength is only 0.27m2 morl.so

interference to cerous ions can be neglected.

The absorbed dose is then calculated as follows 2:

29

Dose,Gy - ., -Y,G\Ce'. )t.p.l

Where:

M : charge in absorbance.

^ / ^ r - \u\Le' ) : Radiation chemical yield of cerous ions : 0.25umol J-lor

{2.4( l00eVr- ' }

t :molar linear absorption coefficient of ce*a ions (561m2mol-1

p :density of the dosimetric solution, Kg--'

I : path length of the dosimetric solution within the spectrophotometric cell

3-2-3 influence of various factors:

This system is influenced by the same and specific factors which alter the

response of Fricke system,with following exceptions (a)oxygen content does

not effects the yield; (b) dose rate effects are minimal; (c)trace amounts of

organic impurities produced very erratic yields; and (d) the system has

definite spectral dependence at energies below 100kvp t.

3-3 Other systems:

3-3-1-aromatic solutes :

Many aromatic compounds such as benzene and benzoic acid undergo

hydroxylation on irradiation in aqueous solution and the amount of product

formed can be related to the dose .for calcium benzoate in water the product

is salicylic acid, the concentration of which can be measured bv its

fluorescence at 400040 excited by 2900,4.0 tignt. 1t;The advantage of these dosimeters is that the solution needed not to be

acidic. The disadvantages include:

a- G (PhOH) is low; being of the order of 1.6

b- Products other than phenol are produced.

30

----------_....................................~~~======--===., --.

Dose, Gy = ( 3)GCe + c.p.!

Where:

M = charge in absorbance.

G(Ce3+) = Radiation chemical yield of cerous IOns = O.25/lmol rlor

{2.4(l OOey)-I}

[; =molar linear absorption coefficient ofCe+4 ions (561m2morl

p =density of the dosimetric solution, Kgm-3

I = path length of the dosimetric solution within the spectrophotometric cell'

3-2-3 influence of various factors:

This system is influenced by the same and specific factors which alter the

response of Fricke system ,with following exceptions (a)oxygen content does

not effects the yield; (b) dose rate effects are minimal; (c)trace amounts of

organic impurities produced very erratic yields; and (d) the system has

definite spectral dependence at energies below 100kvp 1.

3-3 Other systems:

3-3-1-aromatic solutes:

Many aromatic compounds such as benzene and benzoic acid undergo

hydroxylation on irradiation in aqueous solution and the amount of product

formed can be related to the dose .for calcium benzoate in water the product

is salicylic acid, the concentration of which can be measured by its

fluorescence at 4000A0 excited by 2900A0 light. (l)

The advantage of these dosimeters is that the solution needed not to be

acidic. The disadvantages include:

a- G (PhOH) is low; being of the order of 1.6

b- Products other than phenol are produced.

30

c- G (PhoH) shows fairly marked dependences on (phH), LET and dose

rate.

d- The system is too inadequately calibrated to be of great use.

3-3-2 Chlorinated hydrocarbon solutes:

These systems (two -phase) are better thermal stability and higher Radiation

sensitivity; these features permit the preparation of stable dosimeters capable

of registering gammaray exposures covering abroad range (1.0 to t06 Rad).

The chemical reactions are complex, of ten involving chain reactions

consequently the G-values are high so that they can be used to measure low

doses, but they are very sensitive to impurities. It has claimed that the

aqueous tetrachloroethylene system can be used to measure doses in the

range 0.5 to 3.0 Rad with20o/o precision. I

3-4 Potential liquid dosimeters:

Generally, there are many liquids which on irradiation generate intermediate

Radicals and excited molecules which can be reacting with solutes having

strong absorption spectra. These solutions should show indirect action and

might yield useful dosimeter after proper calibration.

Iodine can be regarded as a suitable solute in that; its concentration may be

measured spectrophotometrically, but in aromatic solvents back reaction

occurs which militate against its use.r

Also Diphenyl picryl hydrazyl (DPPH) considered as a suitable solute, sinceit has a high excitation coefficient and G (-DpH) is independent of (DppH)

Radical. over considerable range, however, the mechanism is complex and

G is very dependent on the solvent, being 0.76 inbenzene and high as 35 in

chloroform.

Some inorganic solutes which might be used are (FeCl3, cuCl2) in NN-dimethyl form amide I

31

----------------------,

c- G (PhOH) shows fairly marked dependences on (PhH), LET and dose

rate.

d- The system is too inadequately calibrated to be of great use.

3-3-2 Chlorinated hydrocarbon solutes:

These systems (two -phase) are better thermal stability and higher Radiation

sensitivity; these features permit the preparation of stable dosimeters capable

of registering gamma ray exposures covering abroad range (l.0 to 106 Rad).

The chemical reactions are complex, of ten involving chain reactions

consequently the G-values are high so that they can be used to measure low

doses, but they are very sensitive to impurities. It has claimed that the

aqueous tetrachloroethylene system can be used to measure doses in the

range 0.5 to 3.0 Rad with 20% precision. 1

3-4 Potential liquid dosimeters:

Generally, there are many liquids which on irradiation generate intermediate

Radicals and excited molecules which can be reacting with solutes having

strong absorption spectra. These solutions should show indirect action and

might yield useful dosimeter after proper calibration.

Iodine can be regarded as a suitable solute in that; its concentration may be

measured spectrophotometrically, but in aromatic solvents back reaction

occurs which militate against its use. 1

Also Diphenyl picryl hydrazyl (DPPH) considered as a suitable solute, since

it has a high excitation coefficient and G (-DPH) is independent of (DPPH)

Radical. Over considerable range, however, the mechanism is complex and

G is very dependent on the solvent, being 0.76 in benzene and high as 35 in

chloroform.

Some inorganic solutes which might be used are (FeCI3, CuCb) in NN­

dimethyl form amide 1

31

3-5 Gaseous chemical dosimeters:

These are less important than the liquid phase t1pe, since the dose rate in a

gaseous system may be obtained from ionization current measurement and

W-values (mean energy to create an ion-pair in the substance of interest) or,

if an internal particle source is used under conditions that the rafige of the

particle is considerably less than the containing vessel dimensions, from the

product of the disintegration rate and the mean energy per particle.

The most useful gaseous dosimeter is the use of nitrous-oxide; the

mechanism of which is:

NzO ---) N + NO or N2 * Q,

N + N2O --+ Nz * NO,

O+N2O -> 2NOorNz+Oz

2NO + Oz

G value is independent of temperature in the range -80 "C to 200 oC the

extent of reaction by measuring the amount of NOz

spectrophotometrically, the disadvantage of this dosimeter is that aback

titration becomes important at dose >104 Rad 1.

3-6 Dosimeters based on solids:

These are all rely on the fact that some intermediate is trapped, or causes

some chemical change in a solute or in the gel material itseli which may

be detected calorimetrically, either directiy or after subsequent chemical

development. Such systems are easy to handle and have the possibility of

being made three dimensional; furthermore, back reactions can only be

slow, because of the immobility of the solutes.

In order to obtain reproducible results such dosimeters must be very

carefully prepared and highly standardized procedures.') Ft<l ,/

N20 ----+

N+N2O ----+

0+N2O ----+

2NO+02 ----+

3-5 Gaseous chemical dosimeters:

These are less important than the liquid phase type, since the dose rate in a

gaseous system may be obtained from ionization current measurement and

W-values (mean energy to create an ion-pair in the substance of interest) or,

if an internal particle source is used under conditions that the range of the

particle is considerably less than the containing vessel dimensions, from the

product of the disintegration rate and the mean energy per particle.

The most useful gaseous dosimeter is the use of nitrous-oxide; the

mechanism of which is:

N + NO or N2 + 0,

N2 +NO,

2NO orN2 + O2

2N02

G value is independent of temperature in the range -80 QC to 200 QC the

extent of reaction by measurmg the amount of N02

spectrophotometrically, the disadvantage of this dosimeter is that aback

titration becomes important at dose>104 Rad 1.

3-6 Dosimeters based on solids:

These are all rely on the fact that some intermediate is trapped, or causes

some chemical change in a solute or in the gel material itself, which may

be detected calorimetrically, either directly or after subsequent chemical

development. Such systems are easy to handle and have the possibility of

being made three dimensional; furthermore, back reactions can only be

slow, because of the immobility of the solutes.

In order to obtain reproducible results such dosimeters must be very

carefully prepared and highly standardized procedures.

32

The optical density-dose relation is linear and thus these systems haveobvious potentialities as dosimeters.l

33

t

~----------------======~~~,

The optical density-dose relation is linear and thus these systems have

obvious potentialities as dosimeters. 1

33

CONCLUSION

Based on this review on development of chemical dosirneters,one can

draw the following conclusions remarks:

1-Chernical dosimetcrs are stil l under developing,but an aqueous

chemical dosirneters are preferable because :

2- 'fhey can be prcpared in small containers within body cavitics which

pennits the actual measurcment of Radiation dosc.

3-They are nrore convenient in Itadiation thcrapy.,'/

4-They rnay preparcd hom reagents which arc watcr or tissue eclr-rivalents

in respect to density and Itadiation absorption properlies.

5-The Radiation induced reaction products are relatively stablc and can

be measured directly by color changes or indirectly by simple analytical

procedures.

34

CONCLUSION

Based on this review on development of chemical dosimeters,one can

draw the following conclusions remarks:

I-Chemical dosimeters are still under developing,but an aqueous

chemical dosimeters are preferable because :

2- They can be prepared in small containers within body cavities which

permits the actual measurement of Radiation dose.

3-They are more convenient in Radiation therapy.

4-They may~repared from reagents which are water or tissue equivalents

in respect to density and Radiation absorption properties.

5-The Radiation induced reaction products are relatively stable and can

be measured directly by color changes or indirectly by simple analytical

procedures.

34

flHAPTERFOUR

4- REFERENCES

IHAPTER FOUR

4- REFERENCES

II.EFtrITENCIIS

l - F.S Dainton: Chemical Dosimctry- I ladiat ion Dosimctry

(G.W.lteed, ed), Acadernic press, Nerv York I-ondon (1964).

2- P.G Benny: Iladiation I)osimctry, Radiation Tcchnology

Development Section, Ilhabha Atornic l{esearch Centre, ' l 'rornbay,

Murnbai (lndia)

3- Gordan I-.8 and Gcrald J. i- I . : l tadiat ion Dosimctry, IJoston,

Massachusetts ( 1956).

4- Gunther, P., Von der FI orst, Il.D., and Cronheirn, C.lt., Z.

Elektrochem.34, 6i6 ( 1928).

5- Mi l le r , N. , J :Chcm.Phys.18,79 (1950) .

6- Freund, L . : Wien K l in .Wochschr . 17,412 ( 1904) .

35

- - ------------------

REFERENCES

1- F.S Dainton: Chemical Dosimetry- Radiation Dosimctry

(G.W.Reed, ed), Academic press, New York London (1964).

2- P.G Benny: Radiation Dosimetry, Radiation Technology

Development Section, Bhabha Atomic Research Centre, Trombay,

Mumbai (India)

3- Gm'dan L.B and Gerald 1.1-1.: Radiation Dosimetry, Boston,

Massachusetts (1956).

4- Gunther, P., Von der H orst, H.D., and Cronheim, C.F., Z.

Elektrochem.34, 616 (1928).

5- Miller, N., J :Chem.Phys.18, 79 (1950).

6- Freund, L.: Wien Klin .Wochschr.17, 412 (1904).

35