TRACK FORMATION AND ENERGY OF ALPHA PARTICLE BHABHA ATOMIC RESEARCH CENTRE – INDIA.

TRACK FORMATION AND ENERGY

OF ALPHA PARTICLE

BHABHA ATOMIC RESEARCH CENTRE – INDIA

0 1 2 3 4

unetchable etchable

XCXC

XD

XD

ALPHA INCIDENCES AND TRACK FORMATION


XC

XD

tBC

tt

tBD

TOTAL TRACK ETCH TIME


FACTORS GOVERNING FORMATION OF READABLE TRACKS IN SSNTD

• Energy of incident alpha particle

• Angle of incidence

• Developing the tracks (Etching parameters)

• Counting of tracks


BULK ETCH RATE

Chemical composition of the detector

Etching conditions – Temperature

Concentration

Duration

Preconditioning of the detector


4 6 8 10 120

1

2

3

4

5

6

Y = -0.07 + 0.31 e-(x/4.09)

Temperature : 700C

Vb (

Mm

h-1

)

MOLARITY OF NaOH

Bulk etch rate with molarity of etchant (Gruhn et al., 1979)

0 /0

kTV V e


TRACK ETCH VELOCITY

aRbBT eVRV 1

a= 0.16 m-1 ; b = 2.68

(Andriamanantena and Enge)


Design and parametric validation for LR-115 (type –II) based twin cup dosimeter for

simultaneous measurements of Rn, Tn and progeny concentrations

K.P. EappenHealth, Safety & Environment Group

Bhabha Atomic Research CentreTrombay, Mumbai-400 085, India

Twin cup dosimeter

Rn

Tn

RESPONSE OF LR-115 DETECTOR TO ALPHA PARTICLES IN Rn CUP


6.2 cm

4.1

cm

SSNTD

222Rn 218Po 214Po Cupwall

RESPONSE OF LR-115 DETECTOR TO ALPHA PARTICLES IN Tn CUP


6.2 cm

4.1

cm

SSNTD

220Rn 216Po 212Bi 212Po Cupwall


0.0 0.2 0.4 0.6 0.8 1.00.2

0.4

0.6

0.8

1.0

Theoretical

Experimental

Tr.cm-2/mWL.d : 0.26 + 0.02Eq.Factor (F) : 0.6 - 0.7

Bare detector response with eq.factor (F)

Bar

e ca

rd s

ensi

tivi

ty f

acto

r,

(Tr.

cm2/m

WL

.d)

Equilibrium Factor, F

CALIBRATION FACTORS THEORETICAL & EXPERIMENTAL

(tracks.cm-2 per Bq.d.m-3)

Cup

Radon Thoron

Theore-tical

Experi-mental

Theore-tical

Experi-mental

Mem-brane

0.0234 0.021 - -

Filter 0.0260 0.023 0.0176 0.019

C.F FOR BARE FILM (PER SPECIES): 0.02


L

C0 C1

SSNTD FILM

FUNCTIONAL DIAGRAM OF THE DOSIMETER CUP



02

2

Cdx

cdD

10 CC 0

Lxdx

dc

xx

BeAexC

D

0.56-Transmission ratio /C0

2.187cmDiffusive length (√(D/ξ

0.093cm2 s-1Effective diffusion coefficientDf

4.50cmLength of the dosimeter cupL

0.0564cm Thickness of filter paper

0.0126s-1Decay constant of 220Rn

0.10cm2 s-1Diffusion coefficient of 220Rn in air

D

1.00Bq m-3Thoron concentration at entry point

C0

ValueUnitDetailsTerm

Parameters used for computing transmission ratio

C


dxxCL

CL

0

)(1

LD

LCC

f tanh

10


LCothD

L

C

C

e

C is the average concentration of thoron in the cup C is the concentration of thoron inside the cup at entry point

x = (D/); D = 0.1 cm2.s-1 (Diffusion coefficient of thoron in air) and = 0.0126 s-1 (Decay constant of thoron) is the thickness of G.F filter paper; ( 0.0564 cm)L is the radius of the cup; (6.0 cm)De is the effective diffusion coefficient of

thoron (0.093 cm2.s-1) through filter paper

THORON PROFILE OF INSIDE THE CUP


8 9 10 11 12

0

100

200

300

400

500

600

700

MEASUREMENT OF (Pre-spark 850 V)

Y =

[(a

1-a2

)/{1

+ex

p((

x-x0

)/d

x)}]

+a2

a1=-1

9.65

; a2

=64

4.35

x0=9.

21 ;

dx=

1.18

1

Tra

cks

ob

serv

ed (

Tr.

cm2 )

Track length (m)



0 1 2 3 4

0.010

0.015

0.020

0.025

Variation of Calibration Factor as a function of break-down thich ness () for one hour etching.

Ca

libra

tio

n F

ac

tor

(Tr.

/cm

2/d

pe

r B

q/m

3)

Breakdown thickness, (m)


0 200 400 600 800 1000 1200

0

200

400

600

800

1000

1200

1400

Variation in tracks with prespark voltage

OB

SE

RV

ED

TR

AC

KS

; (t

rack

s cm

-2)

AVERAGE TRACKS; (tracks cm-2)

750 V: Y = 0.87 X 850 V: Y = 1.00 X 1000 V: Y = 1.14 X

Diameters of holes created on LR-115 and Mylar films


r1>100 m

r2= 12 m

RESULTANT AREA

2m

0 200 400 600 800 1000 1200 1400 16000

2

4

6

8

10

12

14

16

ME

AS

UR

EM

EN

T E

RR

OR

(%

)

TRACKS (Tracks cm-2)

y = m X + C

m = 0.01; C = 1.4E-10

Measurement error with increase in track density



21 2

1

2

1 2

where ( )

is the radius of the Al foil hole > 100 m

is the radius of the track hole 6

ST S

a TT T

a r r

r

r

m

CORRECTION FOR SPARK COUNTER

TT – Tracks by microscopeTS – Tracks by spark counter

MODIFICATIONS

Pin hole technique for Rn-Tn separation

Optimization of cup dimensions


Transmission Fractions of Rn &Tn Through Cellophane Membranes

0.8398.0405

0.1489.3030

0.1790.9225

0.2192.6020

0.2894.3515

0.4296.1610

ThoronRadon

Transmission, Ci/Co (%) Cellophane thickness

(m)


C

C0

C : Average radon concentration in the compartment volume space

C0: Outside radon concentration

V : Volume of the compartment

A : Area of the hole

J : Radon activity flux at the hole

d : Thickness of the hole

D : Radon diffusion coefficient in air (hole)

: Radon/Thoron decay constant



CV JA CV

t

oC C

J Dd

0ADCC ADC

t Vd Vd

;TAD

Vd

T e

0( ) 1 etT

e

C t C e

with initial condition ( 0) 0C t , we can arrive at

0( ) 1 etT

e

C t C e

100% response for 6

e

t

95% response for 3

e

t

63% response for 1

e

t

Response time

Transmission factor at 100% response will be T

e


Transmission Fractions of Rn & Tn Through Pin Holes of 2 mm Length

18.7699.9310

12.8799.898

7.6799.806

3.5699.554

0.9299.232

ThoronRadon

Transmission (%) Dia. of the hole (mm)


Response time for Rn & Tn Through Pin Holes of 2 mm Length

31710

3278

4486

41074

44222

ThoronRadon

Response time 95% (min.) Dia. of the hole (mm)


1 2 3 4 5

5

10

15

20

25

30

Thoron transmission with size of entry hole

Tra

nsm

issio

n (

%)

Pin hole size (radius; mm)

Plate thickness 1 mm 2 mm 3 mm 4 mm 5 mm


4.6 cm 4.6 cm

RESPONSE OF LR-115 FILM TO RADON IN CUP

Detector

Radon RadiumA RadiumC' Cupwall


6.0 cm 6.0 cm

RESPONSE OF LR-115 FILM TO THORON IN CUP

Detector

Thoron ThoriumA ThoriumC ThoriumC' Cupwall


6.0 cm 6.0 cm

RADON RESPONSE IN THORON CUP

Detector

Radon RadiumA RadiumC' Cupwall


CONTRIBUTION OF TRACKS(tr.cm-2.d-1/Bq.m-3)

0.060.040.02Radon

0.0790.0550.04 x 0.6 =

0.024Thoron

TotalSurfaceVolume


COMPARISON OF CALIBRATION FACTORS

(Tr.cm-2.d-1/Bq.m-3)

0.0790.019Thoron Cup

0.060.02Radon Cup

Hemi-sphericalCylindricalCup shape


DESIGN PARAMETERS

75 cm2• Filter area6.0 cm• Radius of the cup

Spherical• ShapeThoron Cup

2 mm• Pin hole length1 mm• Pin hole radius4.6 cm• Radius of the cup

Spherical• ShapeRadon Cup


DOSIMETER DESIGN

Bare SSNTD

Tn cup

Rn cup

05.09.0816:32 00


Conclusions…….1. Calibration factors for dosimeter cups depends on:

cup dimensions track development protocols track reading methods

2. Pin holes against filters are better options for separating Rn and Tn in cup dosimeters.

3. Computation of response time enables designing dosimeters with desired exposure period.

4. Optimization of dosimeter dimensions is possible with parametric studies.


………….THANK [email protected]

BBAARRCC

BBAARRCC

mailto:[email protected]

mailto:[email protected]


Eappen K.P, Sahoo B.K, Ramachandran T.V, Mayya Y.S Calibration factor for thoron estimation in cup dosimeter. Accepted for publication in journal Radiation Measurements. Radiation. Meas. 43 S418 - 421(2008).

K.P. EappenFactors Affecting the Registration and Counting of Alpha tracks in Solid State Nuclear Track Detectors. Accepted for publication in Indian journal of Physics (2008)

K.P. Eappen, Y.S. Mayya, R.L. Patnayak, H.S. Kushwaha. Estimation of radon progeny equilibrium factors and their uncertainty bounds using solid state nuclear track detectors. Radiation. Meas. 41 (3), 342 – 348 (2005).

K.P. Eappen, Y. S. MayyaCalibration factors for LR –115 (Type-II) based radon thoron discriminating dosimeter. Radiation Meas., 38, 5 –1 7 (2004).

Y.S Mayya, K.P Eappen, K.S. V. NambiMethodology for Mixed Field Inhalation Dosimetry in Monazite areas using a Twin-cup Dosemeter with Three Track Detectors., RPD, Vol.77, No.3, pp 177-184 (1998)

For further reading……………..

TRACK FORMATION AND ENERGY OF ALPHA PARTICLE BHABHA ATOMIC RESEARCH CENTRE – INDIA.

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