* * * * * » •

TESTING OF RADIOTHERAPY DOSIMETERS IN ACCORDANCE WITH IEC SPECIFICATION

Hannu Järvinen, Erkki Rantanen and Kari Jokela

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Säteilyturvakeskus Sträisäkerhetscentralen

ntre for Radiation and Nuclear Safety

Helsinki, Finland \

STUK-A53

August 1986

TESTING OF RADIOTHERAPY DOSIMETERS IN ACCORDANCE WITH IEC SPECIFICATION

Hannu Järvinen, Erkki Rantanen and Kari Jokela

Finnish Centre for Radiation and Nuclear Safety P.O.Box 268, SF-00101 HELSINKI FINLAND

ISBN' 951-46-9870-3 ISSN 0781-1706

Helsinki 1986. Valtior. painatuskeskus

3

PREFACE

In their position as centres for expertise in radiation

dosimetry and its applications, the Secondary Standard

Dosimetry Laboratories (SSDLs) are expected to advice the

radiation users, the radiotherapy centers in particular, in

selection and use of the most suitable dosimetric equipment.

Various dosimeters are commercially available, but objective

information on their fundamental technical characteristics

is lacking. Such information would be valuable and necessary

for the SSDLs to be able to judge the accuracy and reliability

of the many choices which exist for a given application.

The results of systematic evaluations of dosimeters in a

recognized SSDL (or SSDLs) could be helpful supplementary

information to the other SSDLs and to the radiation users.

In 1983 The Finnish Centre for Radiation and Nuclear Safety

(STUK; old name: Institute of Radiation Protection) and the

International Atomic Energy Agency (IAEA) made a research

contract, the purpose of which was to test selected dosimeters

for use in radiotherapy in accordance with the specifications

by the International Electrotechnical Commission (IEC).

Two common dosimeters (chamber -f mea&uring assemblies) were

selected, manufactured by the Nuclear Enterprises Ltd (UK)

and Physikalisch Technische Werkstatten Dr. Fychlay Gmbh

(FRG). The tests were carried out by the standard dosimetry

section and the section for non-ionizing radiation (external

fields test) at STUK (SSDL-Helsinki). The research was

financed by the IAEA and STUK together, the contribution of

each being 50 %.

4

ABSTRACT

Two common type of dosimeters (chamber + measuring assemblies)

for ase as field instruments in radiotherapy were tested in

accordance with the specifications by the International

Electrotechnical Commission (IEC). The influence of external

electromagnetic fields was determined based on own specifica­

tions. The test methods and equipment are shortly commented

(for external fields test in full details), and the results

are presented in details. The results indicate that the

dosimeters comply quite well with the requirements by the

IEC, while the information supplied with the dosimeters is

quite inadequate. The results of external fields tests

indicate that the dosimeters may be disturbed by external

electromagnetic fields below the susceptility level general­

ly applied to sensitive electronic measuring devices, but

the possible effects can be immediately noticed by totally

erroneous readings.

5

1 GENERAL

1.1 Objective

The objective was to test selected dosimeters for use in

radiotherapy in accordance with the test procedures speci­

fied in the IEC Publication 731 (1982)2.

1.2 Dosimeters tested

The following dosimeters were tested:

I Measuring assembly PTW IQ4, type 764 serial No 040.

2 chambers PTW M233332, serial numbers B330 and B391 ;

the latter chamber was replaced by a chamber No 001

for part of the tests (when No B391 was accidentally

broken).

Stability check device PTW 119, serial No 23261-409.

Note; The original purpose was to test a PTW chamber which by construction would be comparable with the NE 2571 chamber (below). By mistake, however, a chamber type PTW M233332 was supplied for testing. This chamber has a wall thickness larger than that used for ordinary chambers (e.g. NE 2571), and was specially designed (by P. Almond) to minimize the perturbation effect for measurements in a phantom in a 60co beam. The use of this chamber is limited to measurement in 60co beams, and the large energy de­pendence fould at lower photon energies (see page 18) is, therefore, not of importance.

II Measuring assembly NE Farmer Dosimeter 2570, serial

No 305.

2 chambers NE 2571, serial numbers E002 and 182.

Stability check device NE 2503/3, serial No 1265.

The ionization chambers are classified as "unsealed cable-

connected thimble chambers".

Dosimeter I was borrowed from the manufacturer, Physika-

lisch-Technische Werkstatten Dr. Pychlay Gmbh, Freiburg.

Dosimeter II was borrowed from STUK.

6

1.3 Tests performed

The test carried out and selected from the TEC Publication

731 are given in Table I.

1.4 Markings and instructions for use

The markings on the dosimeters and the instructions for

use were checked in accordance with the requirements by

the IEC publication 731. The results are presented in

Appendix B.

2 TEST FACILITIES

The facilities of the Finnish standard dosimetry laboratory

(SSDL-Helsinki) and the section for non-ionizing radiation

(external field tests) at STUK were used. The radiation

sources comprised a 90 TBq (2.5 kCi) 6?>Co source and two

X-ray tubes (Rich. Seifert Isovolt type 400/10 and 150/2O)

connected to a constant potential X-ray generators (Seifert

Isovolt). The exposure rates were measured by a secondary

standard chamber (NE 2561) which is calibrated by the

National Physical Laboratory (UK) in the whole energy range

used. The chambers were precisely positioned in the photon

beams with the help of laser-rays and a special alignment

telescope. The ionization currents from the chambers were

measured by the current integration principle using a

vibrating capacitor electrometer (Keithley 640) and standard

air capasitors (GenRad). For the highest accuracy and

precision, current values were partly obtained by calcula­

tion from a series of measurements using a desk-top computer

(HP 9826A; correcting for stray capacitance and leakage

currents of the electrometer system). The temperature

and the humidity of air in the irradiation room was cont­

rolled by an air-conditioning system ind measured by a

quartz thermometer (HP 2804A) and a humidity indicator (VAI­

SALA HM 14). The athmospheric pressure was measured by a

precision air pressure meter (own construction). The

auxliliary equipment comprised a climatic box (Karl Weiss

7

type 240/40-180, modified for the purpose), a special pres­

sure-test box (own construction), current source Keithley

261 picoampere source and a mains power control unit (own

construction). External fields tests were carried out in

a balanced symmetric stripline, in the open field of a

monopole antenna and in the open field of a horn antenna.

3 TEST PROCEDURES AND RESULTS

As much as possible the test procedures specified in the

IEC Publication 731 were followed. In the following, some

comments, observations or deviations from the specified

procedures will be presented preceeding the results. The

results are given together with the requirement set by

the IEC Publication 731 for a FIELD instrument.

8

Table I. Sununary of the tests carried out and the results. Yes/No: Meets/does not meet the IEC requirements.

Tests for the chamber assembly

IEC 731 Test NE 2571 clause (FS: field size, RO: radiation E002 182

quality)

PTW M233332 B330 B391 001

4.4.1 Leakage current without irradiation 1)

4.4.2 Stabilization time Yes 4.4.3 Post-irradiation

leakage (at60Co, max FS) Yes 4.2.2 Field size

.1 Stem scatter (at 4 RO, 3 FS)

.2 Stem leakage (at 60co, 3 FS) 4.2.3 Chamber orientation

.1 Chamber rotation (at 2 RQ, min FS)

.2 Chamber tilt (at 2 RQ, min FS) 4.2.1 Radiation quality (at 7 RQ) 4.4.4 Exposure-rate dependence 4.4.6 External fields 4.4.7 Guard electrode insulation 4.4.9 Cable strain 4.4.10 Cable connectors 4.6.2 Pressure equilibration 4.6.3 Temperature Yes

1) 1) Yes

Yes

1)

Yes Yes

Yes Yes Yes 2) Yes 3) 4) 1) 1) 1) Yes

Yes Yes Yes

1)

Yes

Yes Yes

Yes Yes 5) x Yes3) 4) 1) 1) 1) Yes

5)

Yes Yes

1)

Yes Yes

B. Tests for the measuring assembly

IEC 731 Clause

Test NE Farmer 2570 305

PTW IQ4 type 764 040

5.7 5.8 5.9 5.10 5.11 5.12 5.16 5.19 5.20

Repeatability Zero drift and zero shift Charge leakage Stabilization time Non-linearity Range changing Temperature Battery power supply Supply mains

Yes Yes 1) Yes Yes Yes No Yes

Yes Yes 1) Yes Yes

Yes2)

Yes

C. Tests for the stability check device

IEC 731 clause

Test NE 2503/3 1265

PTW 119 23261-409

6.4 Repeatability Yes Yes

1) Not possible to compare with the requirement 2) Marginal 3) At the exposure rate used 4) No requirement in IKC 731 5) See Note on page 5.

9

3.1 Tests for the chamber assembly

Leakage current without irradiation (4.4.1)

Comments:

The leakage current was determined from a charge measurement

of 5 minutes duration.

Results:

The results are shown in Table Rl. The minimum rated or

effective exposure rate was not given by the manufacturers,

so the results could no be compared with the requirement.

Table Rl. Leakage current without irradiation: Leakage current (fA) at specified times T.

Chamber:

Polarizing voltage, V:

T 15 min 1 h 6 h

NE 2571 E002

-400

9 4 2

182

-400

7 4 2

PTW M233332 B330

+ 500

1 5 7

B391

+500

<1 1 1

IEC 731 Requirement

< + 1 % of the curren produced by th minimum rate or effectiv exposure rate

10

Stabilization time (4.4.2)

Comments

The chambers were located in a 60co gamma field, 10 cm x 10

cm field size arid about 220 uA/kg (about 50 R/min) exposure

rate. The response at each time was determined as the me^n

value from at least three repeated measurements.

Results

The results are shown in Table R2. The repeatability of

measurements, expressed as the standard deviation of the

mean, was about 0.1 per cent. Both chambers meet the requi­

rement .

Table P.2. Stabilization time: Relative response as a func­tion of time.

Chamber: NE 2571 PTW M233332 EO02 B330

Polarizing -400 +500 voltage, V:

Time 15 min 1.001 1.000 1 h l 1 6 h 0.999 1.001

IEC 731 Requirement

Limits of variation of response + 1 % of its value after 1 h

11

Post-irradiation leakage (4.4.3)

Comments

The highest rated radiation quality appropriate to the scope

of the IEC Public-tion 731 was 60co gamma radiation. The

maximum rated field size was not specified by the manufactu­

rers but was taken to be 40 cm x 40 cm, which is close to

the maximum field size at the treatment distance in clinical

practice. The exposure rate was about 40 uA/kg (about 9

R/min). The transient leakage current after the end of a

10 min irradiation was measured by a current intergrator of

the laboratory, choosing a short (0.5 or 1 s) interval for

the display of the charge and recording the successive rea­

dings in a video tape.

Results

The results are shown in Fig. Rl. For both chambers, the

transient current decreased below the specified value

(+ 1 %) within about 3 seconds (requirement: within 5 se­

conds) after the end of a 10 min irradiation, and therefore,

both chambers meet the requirement.

RELATIVE CURRENT |%!

Fig. Rl. Post-irradiation leakage» The transient leakage current in per cent of the ionization current during the irradiation.

12

Stem S' atter (4.2.2.1)

Comments

The test was carried out at 60 C o gamma radiation and at three

X-ray qualities (Table II). The rated range of . ield sizes

was not given by the manufacturers, but five different field

sizes from 5 cm x 5 cm to 30 cm x 30 cm were used. As a

dummy stem a chamber uimiliar to the one under test was used.

The dummy stem was placed touching the chamber under test

on the side opposite to the real stem, and the actual field

size was chosen so that equal lengths of the stems of both

chambers were always irradiated. At 60Co all chambers were

provided with build-up caps. The usual polarizing voltages

were applied to the chambers (NE -250V and PTW +500 V). At

each energy and field size the mean value from five repeated

measurements was calculated.

Table II. X-ray qualities for the test of stem scatter.

Generating Total filtration*) mm HVL potential Cu Al Be mmCu

75 1.5 3.0 0.064 130 O.lfi 1.84 3.0 0.44 250 2.2 5.0 3.0

*) The inherent filtration of the X-ray tube is included

Results

The results are shown in Table R3. The repeatability (the

standard deviation of the mean) was about 0.1 % (60co) or

0.2 % (X-rays). Neither field size nor energy dependence

of the stem scatter can be postulated, although the response

with the dummy stem in position in general seems to be a

litle higher. Both chambers meet the IEC requirement.

13

Table R3. Stem scatter: (R-1) x 100, where R is the ratio of the chamber response with and without a dummy stem in position.

Length of stem in the field1)

cm

2.5 5 7.5 10 15

Maximum vari­ation of re­sponse iAy/yi, %

NE 2571 E002 kV 75 130 250 60 C o

0.1 0.0 0.0 0.2 0.3 0.1 0.1 0.3 0.0 0.0 0.4 0.2 0.1 0.1 0.3 0.1 0.4 0.1 -0.5 0.0

0.4 0.1 0.9 0.3

PTW M233332 B330 . IEC 731 kV Req. 75 130 250 6 0Co ;

-0.2 0.0 0.1 0.1 0.1 0.2 0.1 0.1 0.0 0.1 0.2 0.1 0.2 0.2 0.1 0.1 0.1 0.2 0.4 0.1

0.4 0.2 0.4 0

Limits of variation of response + 2 %

1) Distance along the chamber axis from the geometric-»! centre of the chamber to the field edge (50 % level of intensity)

14

Stern leakage (4.2.2.2)

Comments

The second of the three test methods proposed in clause

4.2.2.2 of the IEC publication 731 was applied. In the first

measurerrent at each field size the geometrical centre of

the chamber was placed in the field at th<= distance of 3 cm

from the field edge (from the 50 % level of intensity), and

in the second measurement rotated 180° about an axis through

the geometrical centre of the chamber. The test was carried

out at 60co gamma radiation, and maximum rated polarizing

voltages were applied to the chambers (NE -4CC V and PTW

+500 V). At each field size the mean value from five repeated

measurements was calculated.

Results

The results are shown in Table K4. The stem scatter was

neglected when calculating the results. The repeatability

(standard deviation of the mean) was about 0.1 %.

Both chambers meet the IEC requirement.

Table R4. Stem leakage: (R-l) x 100, where R is the ratio of the chamber response with stem in the field and stem away from the field (chamber rotated 1R0O).

Field size Length of stem NE 2571 PTW M233332 IEC 731 in the field*) E002 B330 Req.

cm x cm cm

8 x 8 5 -0.2 -0.1 8 x 1 3 10 -0.3 02) 8 x 13 15 +0.2 0

Maximum variation of response Limits of vari­ation of re-

lAy/yj , % 0.5 0.1 sponse + 1.0 %

1) See Table R3 2) "0": less than 0.05 %

15

Chamber rotation (4.2.3.1)

Comments

The tests were carried out at 60co gamma radiation and at

75 kV X-rays (see Table II). The smallest rated field size

was not given by the manufacturers, but the field size 4 cm

x 4 cm (6°Co) or 0 4 cm (X-rays) was used. Usual polarizing

voltages to the chambers were applied (NE -250 V and PI*'

+500 V). The mean value of five readings at each angle was

calculated.

Results

The results are shown in Table R5. The repeatability (stan­

dard deviation of the mean) was about 0.1 % (60co) and 0.2

% (X-rays). All chambers meet the IEC requirement.

Table R5. Chamber rotation: Relative response as a function of the angle of rotation.

1

Angle of |NE 2571 r o t a t i o n ! ) iE002 182

175 kV 6 0 C o 75 kV 60co

0 90O

190° 2 7 0 °

Maximum v a r i a t i o n of r e s p o n s e | A y / y | , %

1 1 1 1 0 . 9 9 9 0 . 9 9 8 1 .000 0 . 9 9 9 1 .008 0 . 9 9 9 0 . 9 9 8 1 .000 1.006 1.000 0 . 9 9 7 0 . 9 9 8

0 . 9 0 . 2 0 . 3 0 . 2

PTW M233332 B330 001 75 kV 60co 75 kV 6C>Co

1 1 1 1 0 . 9 9 8 1 .000 0 . 9 9 9 1.000 1 .000 0 . 9 9 9 1 .007 1.000 1 .001 1 .000 1 . 0 0 3 1.000

0 . 2 0 . 1 0 . 8 0 . 0 o

IEC 731

Req.

L i m i t s of v a r i a t i o n E r e s p o n s e

+ 1 %

1) Clockwise from the red line (0°: red line towards the source)

16

Chamber tilt (4.2.3.2)

Comments

The same radiation qualities, field sizes, polarizing voltages

and number of repeated measurements were used as in the test

for chamber rotation.

The rated range for the chamber tilt was not given by the

manufacturers, but the minimum rated range required by IEC

731 was used.

Results

The results are shown in Table R6. The repeatability (stan­

dard deviation of the mean) was about 0.1 % (60Co) and 0.2

% (X-rays). All chambers meet well the requirement at 6°Co,

and practically also at 75 kV X-rays (within the repeatability

of measurements).

Table R6. Chamber tilt: Relative response as a function of the angle of tilt.

Angle o f t i l t D

0 + 50 - 5 0

Maximum v a r i a t i o n of r e s p o n s e | A y / y | , %

NE 2571 E002 182 75 kV &0co 75 kV 6 0 C o

1 1 1 1 1.004 1 .003 0 . 9 9 9 1 .000 0 . 9 9 4 1 .002 1 .007 1.000

1.0 0 . 3 0 . 8 0 . 0

1

PTW M233332 B330 001 75 kV 6C ,Cc 7 5 kV 6 0 C o

1 1 1 1 0 . 9 9 9 0 . 9 9 6 1 .001 1.000 1 .007 0 . 9 9 8 1 .011 1 .001

0 . 8 0 . 6 1.1 0 . 1

IEC 731 Req.

L i m i t s of v a r i a t i o n of r e s p o n s e

+ 1 %

1) "+": Stem tilted towards the radiation source

17

Radiation quality (4.2.1)

Comments

The radiation qualities used in the tests are given in Table

III. The irradiation conditions were chosen to correspond

to those usually applied at the calibration of the chamber

i.e. the source to chamber (at 6°Co) or the focus to chamber

(at X-rays) distance of 1 m and the field size of 10 cm x

10 cm (60Co) or 0 10 cm (X-rays). The response of the chamber

was determined in respect of the true exposure. The mean

value of three readings was calculated at each radiation

quality.

Table III. Radiation qualities used in the test of radiation quality.

Generating potential kV

75 100 130 180 200 250

60 r o

Total filtration mm Cu A1 Be

1.50 3.0 3.30 3.0

0.18 1.84 3.0 0.32 5.0 1.10 4.0 2.2 5.0

HVL mmCu Measured Approx. value

recommended by IEC 731

0.064 0.06 0.15 0.16 0.44 0.42 1.09 1-1 1.85 1.8 3.0 3

1 ?

Results

The relative response as a function or radiation energy is

given in Table R7 and shown graphically in Fig. R2. The

response is normalized to unity at 200 kV X-rays. The un­

certainty of response, not evaluated by statistical methods

(Type "B", see1) and caused by this type of uncertainty of

the true exposure, was estimated to be about + 1 % (6C>Co)

and + 1.5 % (X-rays) (approximate "standard deviation"). The

repeatability (standard deviation of the mean) was about

0.1 % (60co) and 0.2 % (X-rays). - The NE chambers practi­

cally meet the IEC requirement. The PTW chambers turned

out to be (after the tests had been finished) special thick

wall chambers ( see Note on page 5), which explains the high

energy dependence. Because their use is limited to 60co

18

gamma rays, this test became irrelevant for them and the

high energy dependence need not be considered.

Table R7. Radiation quality: Relative response as a function of radiation energy.

Radiation quality

NE 2571 E002 182

i PTW M233332 , B330 B391

J IEC 731 Req.

75 kV 100 130 180 200 250

0 . 9 7 4 0 . 9 8 5 0 . 9 9 2 0 . 9 9 8

1 1 .006

0 . 9 8 6 0 . 9 9 6 1.000 1.001

1 1.007

0 . 6 9 0 0 . 7 2 6 0 .H20 0 . 9 4 5

1 1.050

0.693 0.727 0.823 0.946

1 1.047

60 Co !0.994D 0.9901) 1.0701) 1.0661)!

1 iLindts of variation of response ; + 3 %

Maximum :

variation of response |Ay/y | . % for X-rays

43.2 42.4

Difference between 200 kV and 60Co, %

7 . 0 6 . 6 < 5 %

1) wi th bu i ld -up cap

RELATIVE RES»0NSE «—« * »TI « n O — . 0 NC 2571 l|2 * • *rwma»JJJ B130 A _ A i>T«t M mm a » i

Fig. R2. Relative response as a function of radiation energy (HVL).

19

Exposure-rate dependence (4.4.4)

Comments

The test v/as carried out at 60Co gamma radiation at the

exposure rate of 0.72 mA/kg (about 170 R/min) at the field

size of 8 cm x 8 cm, and varying the polarizing voltage.

At the field size used the influence of leakage current across

the insulator on exposure-rate dependence was assumed insig­

nificant, based on the above results of the tests for stem

leakage and post-irradiation leakage.

Results

The results are shown in Fig. R3. The IEC requirement is

satisfied for the recommended polarizing voltage if, for

the maximum rated exposure rate, the measured ionization

current is within 2 % of the saturation current. It can be

seen that both chambers meet well the requirement at the

exposure rate used.

640 •

630

620

550

Sfc5

540

535

500V

r*-2%

N£ 1571 E 007

I (pAl

/ |VI = 250V

PIW MJJ3JJ2 BJI0

|v2| IV2)

10": 10J 2»»"

Fig. R3. Ionization current I as a function of V'2, where V is the polarizing voltage, at the exposure rate of 0.72 mA/kg (about 104 R/h).

20

Exte rna l f i e l d s ( 4 . 4 . 6 )

ComKients

The IEC Publication 731 gives no specification for the test

method and requirements. Therefore, own specifications were

formulated. Because of this and the peculiar nature of the

test, the test method is described in full details in Appen­

dix A.

Results

The results are described in full details in Appendix A.

21

Guard electrode insulation (4.4.7), cable strain (4.4.9)

and cable connectors (4.4.10)

Comments

In the test of guard electrode insulation, the voltage of

the polarizing electrode was that of the guard electrode.

Before the test of cable connectors, the cable and the chamber

assembly were rested for 5 hours with all electrodes connected

together.

Results

The results are shown in Table R8. Because the minimum rated

or effective exposure rate was not given by th>? manufacturers,

the results could not be compared with the IEC 731 require­

ments .

Table R8. Guard electrode insulation, cable strain and cable connectors: current (fA) after 15 min as specified in IEC 731.

Test

Guard electrode insulation

Cable strain

Cable connectors

NE 2571 E002

1

6

8

182

2

1

PTW B330

24

3

7

L

M233332 001

8

IEC 731 Req.

< +1.0 % of the current produced by the minimum rated or effec tive exposure rate

22

Pressure equilibration (4.6.2)

Comments

A special pressure-test box was constructed for this test.

An overpressure between 5 % and 10 % in ambient pressure

was generated with a pump-valve system inside the box, which

contained the ionization chamber and was placed in 60Co gamma

beam (exposure rate about 200 uA/kg (about 50 R/min)).

After 10 minutes irradiation, the overpressure was suddenly

released and the current from the chamber was monitored by

the video-tape method used in the test of post-irradiation

leakage (see above).

Results

The results are shown in Fig. R4. For all chambers the

equilibration time, i.e. the time taken for the change in

ionization current to reach 90 % of the final value of the

change, was less than 10 s (requirement: _i 10 s).

RELATIVE CURRENT » .» NE ( 182) O ' "*3 NE (E002)

Overpressure Ek.... .O Pn»(B330J r . , « , « , A. .M.A P ™ " 0 0 1 '

F i g . R4. P r e s s u r e erfu i 1 i brat- i on : R e l a t i v e c u r r e n t as a f u n d ion of l i m e a f t e r a s u d d e n change of p r e s s u r e .

23

Temperature (4.6.3)

Comments

The rated range for temperature was not given by the manu­

facturers, so the range + 10°C to + 40°C was applied. The

tests were carried out at a climatic box, where the stability

check device was used to provide the constant exposure rate.

At least three hours were allowed for the source container

to achieve temperature equilibrium at each temperature.

The relative humidity of air in the box was within 35 to 65

% during the tests. At each temperature, the mean value of

five readings was calculated.

Results

The results are shown in Table R9. Before calculating the

relative current, the current values were corrected for

temperature, T(oc), and pressure, P(Pa), by multiplying with

the factor C T p:

273.15 + T P TP = 293.15 ' 101325

The repeatability (standard deviation of the mean) was about

0.1 %. Both chambers meet the IEC requirement.

Table R9. Temperature: Relative current as a function of temperature

Temperature °C

9.8 21.5 40.2

Maximum variation of response j A y /y [ * *

NE 2571 PTW M233332 F002 B330

0.998 0.998 1 1

0.997 0.994

0.3 0.6

IEC 731 Req.

Limits of variation of response

± : %

24

3.2 Tests for the measuring assembly

A Keithley 261 picoampere source was used to provide the

input curre: t unless otherwize stated.

Repeatabil/.ty (5.7)

Comments

The minimun effective indicated value was not given by the

manufacturers. It was decided to use the minimum effective

scale reading on the lowest measurement range as the minimum

effective indicated value. Because the minimum effective

scale read'ng (M.E.S.R.) was not given by the manufacturers

either, it was determined from the requirement on "resolution"

as follows:

Resolution <_ + ^ - x (M.E.S.R.)

M.E.S.R. >̂ 200 x Resolution

The following values were thus obtained fcr the minimum

effective indicated values:

NE Farmer 2570

0.6 cc, Low: 0.0500 Gy

charge, Low: 1.000 nC

PTW IQ4

10.3 nF 0.200 V

Results

The results are shown in Table R10. Both instruments (mea­

suring assemblies) meet the IEC requirement.

25

Table RIO. Repeatability: Standard deviation of a single measurement (1- ) calculated from ten successive measurements.

Measuring assembly and range:

Input current: Measuring time:

Mean value of readings:

I. %:

(

NE Farmer 2570 PTW 104

o.6 cc Low Charge Low ; 10.3 nF

50 pA 17 pA 40 pA 25 s 60 s 60 s

0.0579 Gy 1.000 nC 0.229 V

0.26 0 0.25

IEC 731

Req.

_< 0.5 % o the mean value

26

Zero drift and zero shift (5.8)

Comments

The applicaple clause is 5.8.1. The minimum rated input

current (M.R.I.C.) or exposure rate was not given by the

manufacturers, but it was derived from the requirement of

"charge leakage": the minimum rated input current was chosen

so that the measured leakage current was just acceptable

i.e. 1 % of the M.R.I.C. The following values were obtained

(see 5.9):

NE Farmer 2 5 70

0.6 cc, Low: 2 pA

charge, Low: 2 pA

PTW 104

10.3 nF 40 pA

With the above currents the measuring time required to give

the minimum effective indicated value (see 5.7) was 500 s

for NE Farmer 2570 and 51 s for PTW IQ4. Because the time

over which the zero drift is measured should not be less

than these values, the measuring times 500 s and 300 s were

applied, respectively. For all the tests of zero drift the

input was disconnected from the ionization chamber and shi­

elded with a plug.

For NE Farmer 2570 the tests were carried out as follows:

5.8.1 a) The instrument was in the "reset" condition through­

out the period of testing (6 h). The "zero" was

adjusted whenever the arrows in the display appeared

so that they just disappeared. At selected intervals

(15 min, 1 h, 6 h) "start" and "resef'were pressed

by turns, and the momentary reading in the "start"

condition were taken as the zero drift.

71

5.8.1 b) During the 500 seconds measuring period (at selected

intervals) the "zero" was adjusted as above. At

the end of the measuring period, "reset" and "start"

were pressed and the reading in the display after

pressing "start" was recorded as the zero cirift.

The reading was then nulled by adjusting "zero".

5.8.1. c) Tn this case there was no pre-reading (no change

of zero level) in the "start" condition. "Reset"

and "start" was pressed by turns (at selected

intervals) and the reading in the "start" condition

was considered as the zero shift.

For PTW IQ4 the tests were carried out as follows:

Before putting the instrument in operation, the offset tension

and offset current were adjusted according to the instructions

provided by the manufacturer.

5.8.1 a) The instrument was in the "reset" condition thro­

ughout the period of testing (6 h). The reading

at selected intervals was taken as the zero drift.

5.8-1 b) The reading at !_he end of the 300 seconds measuring

period (at selected intervals) was recorded as

the zero drift.

5.8.1 c) "Reset" and "start" were pressed by turns (at

selected intervals) and the reading in the "start"

condition was taken as the zero shift.

Results

The results are 3hown in Table Pll. Both instruments meet

the IEC requirement.

28

Table Rll. Zero drift and shift at 20 °C in per cent as specified in IEC 731 (clause 5.8.1)

Measuring assembly and range:

5.8.1 b) After 15 min After 1 h After 6 h

NE Farmer 2570 0.6 cc Low Charge Low

_ - - 4

0.4 0.5 0.4 0.5 0.4 0.5

PTW IQ4 10.3 nF

oD o 0 0 0 0

IEC 731 Req.

<_ 1.0 *

5.8.1 a), c) ; J After 15 min,i ' 1 h, 6 h J O 0 0 0

1) "0": less than 0.05 %

29

Charge leakage (5.9)

Comments

None.

Results

The results are shown in Table R12. Because the minimum

rated input current was not given by the manufacturers, the

results could not be compared with the IEC 731 requirement.

On the contrary, the results were used to determine the

minimum rated input current (see the comments on 5.8).

Table R12. Charge leakage: The rate of charge loss for a charge of at least 90 % of the maximum stored charge.

Measuring assembly and range:

Full scale:

Charge stored:

Leakage i.e. the rate of charge loss

NE Farmer 2570

0.6 cc Low Charge Low

1.0237 Gy 20.475 nC

0.970 Gy 18.730 nC

1 jiGy/s 20 fA

PTW IQ4

10.3 nF

9.999 V

9.598 V

400 fA (0.04 mV/s)

IEC 731 Req.

< + 1 % of th minimum rated input current

30

Stabilization time (5.10)

Comments

None.

Results

The results are shown i.n Table R13. Both instruments meet

the requirement.

Table R13. Stabilization time: Relative response as a function of time.

Measuring assembly and range:

Average reading:

Relative response after

- 15 min - 1 h - 6 h

NE Farmer

0.6 cc Low

0.5040 Gy

0.994 1

1.004

2570

Charge Low

2.960 nC

0.998 1

1.CO0

PTW 104

10.3 nF

0.994 V

0.999 1

1.003

IEC 731 Req .

Limits of variation of response of the response after 1 h + 1 I

31

Non-linearity (5.11)

Comments

For NE Farmer 2570, five different readings were obtained

by applying a constant current to the assembly and changing

the measuring time (by "set time"; from 25 s to 500 s).

For PTW IQ4, the same procedure was applied except that the

measuring time (from 10 s to 500 s) was controlled manually

using a separate timer and the start/stop keys. To reduce

the uncertainty of the measuring time in the latter case,

the mean value from five measurements was calculated for each

measuring time.

Results

The results are shown in Table R14. The repeatability (s-

tar.dard deviation of the mean) for measurements with PTW

104 was better than 0.05 %. Both instruments meet the re­

quirement. The relatively high deviation of the first reading

with PTW IQ4 may be explained by "a timer error" (manually

controlled measuring time only 10 s).

Table R14. Non linearity: Persentage deviation (Dev) from linearity, i.e. 100 x (mQ/Mq - 1), as a function of scale reading (R).

NE Farmer 2570 0.6 cc

R Gy

0.0500 0.1000 0.2005 0.5015 1.0032

Low

Dev

-0.3 -0.3 -0.1 0 0.0

0.6 cc

R Gy

0.502 1.007 2.015 5.040 10.082

High

Dev

0 0.3 0.4 0.4 0.4

Charge

R nC

1.015 2,010 5.045 10.000 20.220

Low

Dev

0.6 -0.4 0 0.10 0.20

Charge

R nC

10.00 20.05 50.20

100.45 200.95

High

Dev

0 0.3 0.4 0.5 0.5

PTW IQ4 10.3 nF

R Dev V

0.201 1.1 0.500 0.4 1.393 0 3.777 -0.2 9.941 -0.1

IEC 731 Requirement: Limits of variation of response due to non-li­nearity + 1 %.

32

Range changing (5.12)

Comments

This test was only applicaple to NE Farmer 2570, since PTW

IQ4 was provided with only one capacitor (10.3 nF). The

mean value of three readings on each scale was used in calcu­

lating the variation of response.

Results

The results are shown in Table R15. The repeatability (s-

tandard deviation of the mean) was better than 0.01 %. The

instrument meets the requirement.

Table R15. Range changing: Variation of response for the two ranges of NE Farmer 2570.

Range:

Mean value of r e a d i n g s :

Di f fe rence in per cen t between "Low" and "High"

0.6 cc Low High

0.9496 Gy 0.950 Gy

0.04

Charge Low High

10.060 nC 10.05

0.10

i

nC

IEC 731 Req.

Limits o v a r i a t i o

of respons + 1.0 %

33

Temperature (5.16)

Comments

For NE Farmer 2570, the rated range given by the manufacturer

was lOOc to 3 5°C, and for PTW IQ4 the rated range was not

given by ih<: manufacturer. Therefore, +35°C was used as

the highest temperature in the tests for KE Farmer 2570,

and +40°c for PTW IQ4. The relative humidity of air was

about 55 % at 1C-C, 45 I at 20°C, and 30 % at 35°C and

40°C. For the measurement of variation of response, mean

value of five readings was calculated at eech temperature.

Results

The variation of zero drift as a function of temperature is

shown in Table R16, and the variation of response with a

constant input current as a function of temperature is shown

in Table R17. The repeatability (standard deviation of the

mean) in the latter case was better than 0.05 *. The zero

drift with NE Farmer 2570 at 350C exceeds the limit set by

the IEC, and the variation of response as a function of

temperature with PTW IQ4 very slightly exceeds the limits

of variation set by the IEC (no correction factors were

supplied).

34

Table R16. Temperature: Zero drift as a function of temperature, in per cent of the rate of change of indicated value produced by the minimum rated input current.

Measuring assembly and range:

NE Parmer 2570

0.66 cc Low Charge Low

PTW IQ4

10.3 nF

IEC 731

Temperature, oc:'l0 20 35 10 20 35 i 10D 20 40

t' 5.8.1 b) After 15 min After 1 h After 6 h

0 0 0

0.4 0.4 0.4

3.4 3.4 3.0

0 0 0

0.5 0.5 0.5

3.5 3.5 3-5

o 0 0

0 0 0

0 0 0

5.8.1 a) After 15 min Ih, 6h

Maximum vari­ation of zero drift from the value at 20o, in per cent as specified by IEC 731 3.0

0 0 0 0 0 0

3.0 < + 1.0 %

1) At this temperature the "Th-lighf not go out.

of PTW IQ4 grew dim but did

Table R17. Temperature: Variation of response with a constant input current as a function of temperature.

Measuring assembly and range:

NE Farmer 2570 ! PTW 104

0.6 cc Charge 10.3 nF Low High Low High

IEC 731 Req.

Mean reading a t 20°C:

Re 1 a t- i VP

reading at + 10°C + 20°C + 3 50C + 40°c

Maximum variation response 'y/y , %:

0.5031 Gy

,003 1

.999

of

0 . 4

3.539 nC

1.004 I

0.990

0 . 5

1.166 V

0.997 1

0.988

1 1.2

Limits of vari­at ion of r e ­sponse + 1.0 % (if no correc­t ion factors supplied)

it;

3attery power supply (5.19)

Comments

The test of battery voltage (5.19.1) was carried out for NE

Farmer 2570. For this test the instrument was used about 4

hours per day. Ac the end of each period of 4 hours five

repeated measurements were carried out at a constant input

current (0.1 nA), and the mean value calculated.

Results

The results of the test of battery voltage (5.19.1) are shown

in Table R18. The repeatability (standard deviation of the

mean) was better than 0.05 %. The instrument meets the I EC

requirement.

Table R18. Battery voltage: Relative response with a constant input current as a function of life of batteries, for NE Farmer 2570.

L i f e t i m e of b a t t e r i e s

h

4 8

12 16 20 2 4 D

Maximum v a r i a t i o n r e s p o n s e . ! A y / y | , %:

of

0 . 66 cc

1 0 . 9 9 8 0 . 9 9 6 0 . 9 9 8 0 . 9 9 9 0 . 9 9 8

0 . 4

Low C h a r g e Low

1 1 .997 0 . 9 9 8 0 . 9 9 8 0 . 9 9 8 0 . 9 9 9

0 . 3

IPC 731 Req.

L i m i t s of v a r i a t i o n of r e s p o n s e

+ 1 %

1) At the end of the last period of 4 hours the red "battery low" light appeared.

3ft

Supply mains (5.20)

Comments

The test of mains voltage (5.20.1), mains voltage variations

during a measurement (5.20.2) and mains frequency (5.20.3)

were carried out for PTW 104. For each value of the influence

quantity, mean value of five readings was calculated. For

the test of mains voltage variations during a measurement,

a chamber PTW M233332, serial number B391, was connected

to the measuring assembly.

Results

The results are shown in Table R19. The repeatability (s-

tandard deviation of the mean) was better than 0.05 %. The

instrument meets the IEC requirement.

Table R19. Supply mains: Relative response as a function of mains voltage or mains frequency, for PTW 104, 10.3 nF

Mains voltage (5.20.1) 19.1.6 V 220 242

Maximum variation of response ' y/y , %:

Rel.response 1.001

1 1.003

0.3

Mains vo l t age R e l . r e s p o n s e dur ing measurement ( 5 . 2 0 . 2 )

220 V 1 193.6 -> 242 1.001 242 -> 193.6 0.997

Maximum v a r i a t i o n of i n d i c a t e d value of the minimum e f f e c t i v e i n d i c a t e d v a l u e * ) , %: 0,4

Mains frequency R e l . r e s p o n s e ( 5 . 2 0 . 3 )

49 Hz 1.00 5 50 1 51 1 .006

Maximum variation of response y/y , %: 0.6

IEC 731 Req.

Limits of variation of response + 1 %.

Limits of variation of the indicated value value of the minimum effective indicated value + 1 %

I

J_

Limi ts of v a r i a t i o n of r e s p o n s e + 1 %.

I ) 5>ee comments on " R e p e a t a b i l i t y " (5 .7 )

37

3.3 Tests for the stability check device

Repeatability (6.4)

Comments

Both dosimeters were provided with overall stability check

devices (category b).

Results

The results are shown in Table R20. Both devices meet the

IEC requirement.

Table R20. Repeatability: Standard deviation of a single measurement as determined from ten successive measurements.

Chamber and Stability check measuring assembly device

Standard deviation %

IEC 731 Req.

NE 2571 (E002) NE Farmer 2570

NE 2503/3 (1265) 0.37

< 0.7 % PTW M233332 (B391) PTW 119 (23261-409) 0.05 PTW IQ4

38

4 SUMMARY AND CONCLUSIONS

The results of the tests ire summarized in Table I (page

8), where it is shown for each test whether the ionization

chamber or the measuring assembly meets the IEC requirement

or not.

In general, the dosimeters tested comply quite well with the

IEC requirements. In two cases (expressed as "marginal" in

Table T) the measured variation of response slightly exceeds

the limits specified by the IEC, but the excess variation

is close to the estimated uncertainty of the measurement.

Only in one case (test 5.16 for NE Farmer 2570: zero drift

as a function of temperature) the measured variation of

response clearly exceeds the specified limits (variation

about 3 %, limits + 1 % ) , but the result of this test is of

little practical importance. The very large variation of

the response of the PTW M233332 chamber as a function of

radiation energy is explained by the exceptionally thick

wall of the chamber, the fact which was not known at the

time of testing and which made the test irrelevant (see pages

5 and 18).

Many of the results could not be compared with the IEC re­

quirement because of inadequate information supplied with

the dosimeter by the manufacturer. The markings on the

dosimeters and the instructions for use were also inadequate

when compared with the IFC requirements (Appendix R).

For the "external fields" tests, the IEC publication 731

specifies no test methods or requirements. The results of

tests (Appendix A) indicate that the dosimeters may be dis­

turbed by external electromagnetic fields below the suscep­

tibility level generally applied to sensitive electronic

measuring devices. This type of disturbing fields are likely

to appear in the environment of radiotherapy accelerators,

but fortunately trie possible effect on dosimeters can be

immediately noticed as totally erroneous readings.

REFERENCES

1. Comite International des Poids etMesures, Recommendation

1 (CI-1981); Assignment of experimental uncertainties.

2. International Electrotechnical Commission (IEC): Medical

electrical equipment: Dosimeters with Ionization Cham­

bers as used in radiotherapy, IEC Publication 731, 1982.

APPENDIX A 1 (16)

THE EFFECT OF RADIO-FREOUEN'CY AND MICROWAVE RADIATION ON RADIOTHERAPY DOSIMETERS

1 INTRODUCTION

Numerous electrical equipment emit intense parasitic radio-

frequency (RF) electromagnetic (EM) radiation which may

disturb the functions of other electrical devices. Require­

ments for the control of electromagnetic interference (EMI)

are particularly stringent strict in hospital environment

where malfuctions of sensitive electrical measuring devices

must, be avoided.

Examples of EMI generating applications in medicine are

electrosurgical devices, microwave diathermy units, hypert­

hermia applicators for cancer therapy and microwave driven

accelerators.

Especially serious EMI problems may arise in radiation

therapy departments. Microwave accelerators typically

produce 2 to 4 MW pulse powers at 3 GHz frequency with

pulse repetition frequencies (PRF) from 200 Hz to 500 Hz.

Also, the pulse modulation circuits give rise to very

broadband (1 MHz to 1 GHz) noise peaks with the same PRF.

Another example is the hyperthermic therapy, a promising

new modality which in most cases will be used in conjunction

with the conventional radiaton therapy. The frequencies of

RF- hyperthermia extend from 1 MHz to 2.45 GHz and the RF-

power from 30 W to 1.5 kW. The typical leakage radiation

levels in microwave hyperthermia commonly exceed the suggested

safety limit of 100 W/m^ at 5 cm from the surface of a patient-

simulating phantom . At longer distances the power density

varies roughly as a function of the inverse square of the

distance, which implies that the electric field strength is

below 1 V/m (2.65 mW/m2) at distance roughly 10 m or more

when no absorbing walls are present. Also, conventional HF-

diathermy therapy equipment emit interfering stray fields;

2

the electric fields around an ordinary 27 MHz diathermy

unit equipped with capacitive plate electrodes is typically

of the order of 100 mW/m2 at the distance of 2 to 3 m from

the electrodes. The distance of 1 V/m electric field

strength is then about 100 m.

Very little data has been published on the EMI susceptibility

characteristics of dosimeters used in radiation therapy.

The test results for commonly used radiation protection 9 3 4 ft 7 ft

survey meters ' reveal that especially the ionizing

chamber monitors are sensitive to EMI if they are not

specifically shielded ' . This is due to low current

levels requiring high input impedances and a large DC

gain. For example, power densities as low as 1 mW/m2 at 3 58.3 MHz may interfere with an ionization chamber monitor .

This appendix deals with EMI susceptibility tests for NE Farmer

2570 and PTW IQ4 ionization chamber dosimeters. The tests

were carried out at frequencies from 10 MHz to 100 MHz and

at 2.45 GHz. The test system will be described in Chapter

2 and the results are presented and discussed in Chapter 3.

2 TEST METHODS

2.1 High frequency tests

The basic method for EMI susceptibility tests is to expose

the test object to an accurately known electromagnetic field

and observe whether the test object functions correctly.

The high frequency tests were carried out in the frequency

range from 10 MHz to 100 MHz, where the test fields were

generated in a balanced symmetric stripline, see Figure 1.

The radio- frequency (RF) input signal was in most cases a

1 kHz square pulse train, amplified before feeding it to the

stripline through directional power meter R§S Naus 3 which

measures both the forward and reflected RF-powers. In case

the input power P i n w a s less than 0.05 W it was determined

from

3

Pin = P0.05 x 1 0

L0.05~Lin

w— (1)

where ^ 0_ 0 5 and L^n are the readings in decibels of a variable

attenuator corresponding to the input power of 0.05 W and

the the input power to be measured, respectively. Harmonic

frequencies may cause an error if the interference level is

low at harmonics. To eliminate this error, the output signal

of the amplifier was filtered with 45 MHz or )0 MHz low-pass

filters.

BALANCED

SYMMETRIC STRIPIINE 2 o = 200 n

G

- T L

FREQUENCY COUNTER

G o

«RIABI.E UlENUAtOR S - S 6 d B

_£ s*> )

PULSE SIGNAL MOOULAriCW GENERATOR GENERATOR 10-500MHJ

POWER LOW-PAS' AMPl'F.'E" TIMER 15-SOOMHJ 9 5 W

LJ—

Figure 1. Balanced symmetric stripline system for EMI susceptibility measurements from 10 MHz to 100 MHz. a) Block diagram, b) Detailed drawing of the stripline and test arrangement for radiation therapy dosimeter with spread cable coil.

Since the KM I sensitivity of the dosimeters varies very

strongly and rapidly as a function of the frequency, a fre­

quency counter (HP 5342A) was needed to repeat the test

4

frequencies accurately in order to enable accurate comparisons

between different test conditions.

The balanced syrrmetric stripline shown in Figure 1(b) consists

of two parallel metallic plates and tapered transition sec­

tions. The stripline functions as a symmetric 200 trans­

mission line matched with balun transformers to the asymmetric

50 coaxial system. Additionally, the baluns improve the

symmetry of the line by allowing only opposite, odd mode,

currents to flow through the line.

In the re flectionless ideal case the electromagnetic field

between the plates simulates the free space condition, in

which case electric field E is perpendicular to magnetic

field H and the power density S is given by

«j - y2 - n 2 - PinZo , (2) b — — — \\ n — ~

where E and H are the RMS values, P. is the radio-frequency

input power, 7 (200 ) is the characteristic impedance of

the line , and n is the free-space characteristic impedance

r, = J L = 376.7 . (3) H

The a c t u a l e q u i v a l e n t e l e c t r i c - and m a g n e t i c - f i e l d power

d e n s i t i e s fip and Sfj, r e s p e c t i v e l y , were determined wi th

a c c u r a t e l y c a l i b r a t e d ' f i e l d s t r e n g t h meters H1-3003/GRF-03

and HI-3OO2/STH-02. The c a l i b r a t i o n a c c u r a c y was b e t t e r

than + 1 dB.

F igure 2 shows the average e q u i v a l e n t power d e n s i t i e s as a

f u n c t i o n of t h e f r equency w i t h input power P. =1 w. The

r e f l e c t i o n s from t r a n s i t i o n s e c t i o n s cause a s t a n d i n g wave

in the l i n e . Thus, t h e equ iva l en t power d e n s i t i e s of e l e c t r i c

and magnetic f i e l d s d e v i a t e from each o t h e r and t h e f i e l d s -

become inhomogeneous in l o n g i t u d i n a l d i r e c t i o n . The r a t i o of

maximum to,1 minimum power d e n s i t y was, howeve r , l e s s t h a n

2.6 dB for both E- and H-fields up to 80 MHz and the input

return loss remained above 10 dB. Above 50 MHz the power

densities decrease due to increasing radiation losses.

Figure 2. FREQUENCY [MHz|

Measured equivalent power density averaged over three points on the centerline of the symmetric balanced stripline. The theoretical value is calculated for ideal matched and lossless case.

The test field intensity is characterised in the following

by equivalent electric field power density or field strength,

since the electrical coupling probably dominates over the

magnetic coupling and the most relevant requirements for

EMI tolerance9'10 are given as F-field units above 50 Hz.

The equivalent power density will be given in most cases as

decibels in regard of 1 W/m2 (s = 10 log._S). CI D If)

The tests were carried for three different cases. Figure 1(b)

shows the test arrangement where the ionization chamber and

its cable (10 m for Farmer and 6 m for PTW) was wound in

the form of a spread solenoid around a square styrox core

of 40 cm width. The length of the solenoid was about 20 cm

and the space between the turns about 5 cm. This arrangement

was chosen to obtain the maximum coupling tc. the test specimen

without excessive loading the line. In the second case the

cable was wound tight without any space between turns and

the loop plane was tilted 45° in respect of the magnetic

6

field direction. Note that in the center the magnetic field

lines are perpendicular to the long axis and parallel to

the plates. Electric field lines run from one plate to

another. In the third case, both the chamber and the cable

were disconnected from the measuring assembly, and the latter

was placed alone into the center of the stripline. The test

system and test procedures described above are quite similar

to those used by PTB (Physikalisch- Technische Bundesansta-

lt) in the Federal Republic of Germany ' . In the test

spefifications of PTP the cables inside the stripline are

horizontal and 1 m long, which is the main difference.

For the PTW dosimeter the power line cable was placed per­

pendicular to E field and equipped with an RF filter to

minimize the coupling through the power line. The interfe­

rence suppression is necessary because disturbances carried

by the power line are coupled through uncontrolled stray

fields outside the test space.

To obtain test results in a more realistic situation, where

also power- line-coupled disturbances may be included, and

to investigate the reliability of the stripline method, some

measurements were repeated using the open field system shown

in Figure 3. The test fields were generated with a monopo^e

antenna tuned near to quarter- wavelength resonance. The

power feed and power measurement arrangements were identical

with those in the Figure 1. The relative orientation of the

electric field .n regard to the test object was similar to

the stripline case. However, the magnetic field has been

rotated 90 degrees in the horizontal direction. The distance

between the antenna and the test object exceeded the reactive

field limit v /2 i' at all the other frequencies except at 20

MHz, which implies that the difference between Sp and Sfj

would remain in most cases below 6 dB. The agreement between

the results obtained with different test setups is good except

at non-resonant frequencies for the PTW meter, see Figure

4. At these frequencies the coupling through the power line

dominates and this coupling mechanism is clearly different

in the stripline system when compared to the open field

system.

RF-POWER

ADJUSTABLE N / ' MONOPOLE

SPREAD CABLE COIL AND CHAMBER

METER PART (PTW)

200 cm

| ^ POWER LINE

E

\ METALLIC GROUND PLANE

SIDE VIEW

Figure 3, Open f i e l d t e s t arrangements for EMI s u s c e p t i b i ­l i t y t e s t s a t h igh f r e q u e n c i e s .

10 -

% y 0

CO TJ

V *~ - to -1/1 t v

UJ

£X UJ -20 • 3 o a.

5 -30

> Z) O ^ -/. Q -

"* \\ l PTW . 1 / MON0P01E \ U

B PTW /NsTRIPLiNE

/ ' / * / 'Ä

i C l '7, \ >- 9 A 1 /" \ /

rtT \ /' M \ i

1 /'

FA RUE P STRIPLINE

P -S'* -

p FARMER / ' M0N0P0LE

10 20 30 40 50 60 70 80

ffiEQUENCY | M H * I

Figure 4. Comparison of EMI susceptibility levels of radiation therapy dosimeters measured in the open field and stripline test systems.

2.2 Microwave tests

The microwave measurements were carried out in an anechoic

chamber in the far field of a horn antenna, see Figure 5.

The distance from the antenna was 2,75... 3,50 m and the

relative orientation of the test object in regard to the E

field and wave propagation direction (k) is shown in the

figure.

8

POWER METERS MP 1-3SA

ATTENUATOR 3 dB OR TOdB

'zona

MICROWAVE POWER GENERATOR 2 45 GHJ 20-200W

DIRECTIONAL COUPLER MAR 0 1 3022

POWER METER HP LK A

TUNING (v) SHORT

SCREWS ^

" I \

PROBE

ora WR 29*.

COAXIAL WAVEGUIDE ACAPTER

S J B N ^ MORN

ANTENNA G-1S 2dB

- —

DEVICE UNDER TEST

Figure 5. Microwave F.MI susceptibility test system.

The microwave power was obtained from diathermy generator

Siemens Radiotherm 304, which produces high duty cycle pulses

(PRF = 50 Hz, pulsewidth = 3.0 ms). The input power of the

horn antenna (P' ,) was first measured using low power with

the precision directional coupler Narda 3022 and the power

meter HP 435 A. The reference power P" - in the output

connector of a short probe was also recorded. The input

power in high power test conditions is then obtained from

P . = P in

ref

ref

( 4 ;

where Pm is the measured power in the probe output. The

use of weakly coupled probe eliminates the error due to

possible heating effects in attenuators.

Finally, the power density is solved using the well known

formula

S ( r) = G Pin A V r2

(5)

where G is the accurately determined gain (+ 0.35 dB) of

the antenna. The total uncertainty of the power density is

estimated to be + 2 dB. A more detailed description of the

system can be found in reference .

3 RESULTS AND DISCUSSION

3-1 High f r e q u e n c y t e s t s

The minimum s u s c e p t i b i l i t y l e v e l of NE Farmer 2570 and PTW

IQ4 d o s i m e t e r s measu red i n t h e s t r i p l i n e a r e g i v e n i n F i g u r e s

6 and 7 a s a f u n c t i o n of f r e q u e n c y . The RF-power was g r a ­

d u a l l y i n c r e a s e d u n t i l t h e f i r s t s i g n s of a b n o r m a l f u n c t i o n s

a p p e a r e d i n t h e d i s p l a y when m e a s u r i n g t h e i o n i z a t i o n p r o d u c e d 90 by a 33 MBq S r s o u r c e in c o n t a c t w i t h t h e c h a m b e r . In

g e n e r a l , t h e d i s p l a y showed t o t a l l y e r r o n e o u s m o m e n t a r y

r e a d i n g s w i t h i n 3 dB above t h i s minimum l e v e l f o r b o t h t e s t

o b j e c t s . However, b o t h m e t e r s t o l e r a t e d much more i n t e n s e

f i e l d s w i t h o u t m e a s u r e m e n t e r r o r s ; o n l y t h e d i s p l a y was

d i s t u r b e d i n t h e f i e l d . The power d e n s i t y where m e a s u r e m e n t

e r r o r s a p p e a r e d was a b o u t 27 dB above t h e minimum i n t e r f e r e n c e

l e v e l f o r Farmer ( 3 8 . 5 4 MHz) and 41 dB f o r PTW ( 3 3 . 1 3 MHz).

ID

10 -

0 -

& -10 z LLI O

ft: -20 -

-30

! -40

TEST LIMIT

10V/m

^ 3 _ ^ j _ COMPACT CABLE

•A- -A- CABLE DISCONNECTED

- 1 —

10 —p-

20 30 — i —

40 50 —r~ 60

— i —

70

— i —

80 — i —

90 100

FREQUENCY [MHz I

Figure 6, EMI susceptibil ity levels of NE Farmer dosimeter as a function of frequency measured in the symmetric balanced stripline.

10

I I 1 1 1 1 1 1 1

0 10 20 30 40 50 60 70 80 90 100

FREQUENCY [MHz! Figure 7. EMI susceptibility levels of PTW 1Q4 dosimeter

as a function of frequency measured in the symmetric balanced stripline.

The curves in Figures 6 and 7 do not in all details follow

the true EMI characteristics of the dosimeters, since most

measurement points were selected at fixed frequencies and

the susceptibility levels vary very sensitively as a function

of frequency. The minimum points, however, were carefully

screened. The curves clearly show that it is necessary to

perform broadband measurements with small frequency intervals

and not to rely on few discrete frequencies.

At most frequencies the disturbances are coupled through

the chamber and its cable, which is obvious when comparing

the curves for the detached cable case (only the measuring

assembly in the field) with the other test results. At some

narrow frequency bands the cable resonates, causing a drastic-

increase of the EMI sensitivity at these frequencies.

The spreading of turns clearly enhances the sensitivity.

In this case the minimum power densities are -36 dB , '> for W/m-

Farmer ( 5 3 . 4 4 MHz) and - 3 4 A\im2 f o r P T W (33.6 MHz). At

other frequencies the PTW dosimeter is apparently be t te r .

However, the coupling through the power line cable reduces

11

the EMI tolerance to the same level as for Farmer, as can

be seen from Figure 4.

The effect of pulse modulation parameters was also studied

by keeping the average power density constant and by varying

the pulse parameters. The pulse width was varied from 7.5

us to 0.5 ms (PP.F = 1 kHz) and the pulse cycle was varied from

100 us to 50 ms with a fixed 50 % duty cycle. Variation

in the susceptibility levels of PTW remained within + 1-

dB. For Farmer the changes were somewhat larger, being however

within + 6 dB.

The present results can be compared with the susceptibility

limits presented in the EEC draft directive that is referred 9 10 to in references ' . According to the draft, the electronic

devices incorporated in or associated with measuring instru­

ments must be able to tolerate electromagnetic radiation up

to 10 V/m (265 mW/m2) in the frequency range from 0.1 MHz

to 500 MHz and 1 V/m (2.65 mW/m2) from 500 MHz to 1000 MHz.

The minimum interference level of the tested dosimeters is

about 30 dB below the limit.

3.2 Microwave measurements

The results for 2.45 GHz measurements are given in Table I

which shows that the interference level varies from -2.5 to

7.5 dB,, o. in most cases the cable arrangement are much W/m^

less critical than in the previous measurements, which indi­

cates that EMI is coupled directly through the enclosure.

1 o

Table I Minimum interference levels at 2.45 GHz for radiation therapy dosimeters

Power density dB,,, o

dosimeter 7̂E Farmer 2570 PTW 104

spread cable coil 7.5 3.4

compact horizontal

cable coil 3.4 4.9

compact cab le c o i l , t i l t e d t o 45° - 2 . 5 5.4

measuring assembly a l o n e 7.5 5.4

No general EMI susceptibility standards exist for the fre­

quencies above 1 GHz. However, the results can be compared

with some typical leakage radiation levels. For the proposed

leakage radiation limit of 100 W/m2 (5 c m from the device)

for hyperthermia systemsl, the interference distance is

roughly 0.5 m at 2.45 GHz. It should be noted, however,

that for pulse devices having low duty cycle (e.g. microwave

linear accelerators) the interference levels may change

although the high frequency measurements with a low duty

cycle indicate that the average power density determines

the interference levels. Since the leakage radiation of

microwave accelerators is, however, usually less than 1 W/m2

over 15 cm distances, the microwave radiation is not the

most probable source of interference, ^he radiation emitted

from pulse modulation circuits may bo of more significance.

SUMMARY

The effect of electromagnetic interference {EMI) on ionization

chamber radiation therapy dosimeters was studied in the

frequency range from 10 MHz to 100 MHz and at 2.4 5 GHz.

The tested instruments were NE Farmer 2570 equipped with

1 3

chamber model 2571 and PTW-IQ4 equipped with chamber model

M233332.

The high frequency tests were carried out in a balanced

symmetric stripline and in front of a quarter-wavelength

monopole. The agreement of comparable measurement results

was within 5 dB. The interference level was at its minimum

when "he cable connecting the chamber with the measuring as­

sembly was wound around a styrox core. The minimum electric

field strength, which caused functional disturbances, was

for both dosimeters about 30 dB below the suggested limit

10 V/m (- 6.02 dB , 2)- The corresponding frequencies were

33 MHz for PTW and 53 MHz for Farmer dosimeter. The

interference level minima appeared at very narrow frequency

bands where the cable coil tuned into the resonance. When

the cable was disconnected, the interference level for both

dosimeters rose above 10 V/m. Thus, the coupling through

cables determined the interference susceptibility in the

frequency range in question. Most tests were performed using 1

TcHz square pulse modulation. The decrease of pulsewidth,

from 0.5 ms to 7.5 us does not considerably change the

interference levels, if the average power density is maintained.

The minimum interference level was defined as the level of

average (equivalent) power density or electric field strength

(RMS) where the first signs of disturbance appeared in the

display. Although the display showed erroneous results

during the measurement, the correct display was restored

when turning off the RF exposure. The exposure level where

permanent measurement errors appeared was about 27 dB and

41 dB above the minimum interference level for Farmer and

PTW dosimeters, respectively.

The microwave tests were carried out in an anechoic chamber

in the far field of an horn antenna using a CW magnetron as

a power source. The uncertainty of the measured interference

levels was estimated to be within + 2 dB. The minimum

interference level was - 2.5 dB,,, -j. The cable configuration

was not critical, which indicates that interfering signals

are coupled directly through the enclosure.

14

The test results show thut the tested dosimeters may be

disturbed near high-power RF-devices. The most likely

sources of interference in connection with radiation therapy

equipment are hyperthermic devices and the pulse modulation

and microwave circuits of linear accelerators.

1 5

REFERENCES

1 Bassen HI, Coakley C:. United States safety and regulatory

considerations for radiofrequeney hyperthermia systems.

Journal of Microwave Power 1981: 10(2): 215 - 226.

2 Casbolt PN. O'RiordanMC. An evaluation of the performance

of ionizing radiation measuring instruments in non-ionizing

electromagnetic interference fields. In International

colloquium on Radiological Protection Problems Associated

with Parasitics with X-ray Emission and Electronic Produ­

cts. (Proc), Tolouse, 1970.

3 Frazier JR, Ohlhaber TR, Ruggera PS. Performance of X-

ray measurement instruments when subjected to environmental

level RF Fields. HEW Publication (FDA) 78 - 8065. U.S.

Department of Health, Education, and Welfare, Food and

Drug Administration, 1978.

4 lies WS, Blundell DR, Callowhil1 K, White DF . Instrument

evaluation no. 6, Victoreen 440 RFA, Shielded low-energy

X-ray survey meter. Report NRPB-IE6. Harwell, Didcot,

Oxon: National Radiological Protection Board, 1976.

5 Jokela K, Puranen L. Evaluation and improvement of the

accuracy of TEM transmission cells with internal field

measurements. In 13th Furopean Microwave Conference (p-

roc). Nurnberg, 1983: 652 - 6557.

6 Langlet I. Modification of an ion chamber instrument

for elimination of interference from RF-fields.

Report SSI: 1976 - 35:E. Stockholm: Statens sträls-

kyddsinstitut, 1978.

7 Langlet I. investigation of the PF sensitivity of instru­

ments for ionizing radiation, Part 1: screening test

in different types of RF irradiation. Report SSI: 78

-035:E. Stockholm: Statens stralskyddsinstitut, 1978

16

8 Langletl. GrapengiesserS. Jndersökning av RF-känslig-

heten hos strålskyddsinstrument, del TI. Report SSI:

1978-032. Stockholm: Statens strålskyddsinstitut 1978.

9 NolteG. Prufungen auf Beeinflussung eines Gerätes durch

äussere elektrische, magnetische und elektromagnetische

Störungen. In Hohlfeld K., Reich H. (eds.). Aktuelle

Fragen der Dosimetrie fiir Photoner.strahlung in der Strah-

lentherapie und Diagnostik. Report PTB-DOS-6.

Physikalisch Techr.ische Bundesanstalt, 1981: 65 - 70.

10 PTB-Prufregeln, Störfestigkeit. Braunschweig und Berlin:

Physikalisch - Technische Bundesanstalt, 1984.

11 Puranen L. Development of microwave hazard monitor

calibration system. Report S163. Helsinki: Helsinki

University of Technology, Radio Laboratory, 1985.

APPENDIX B

MARKINGS AND INSTRUCTION FOR USK

The markings on the dosimeters and the instructions for their

use were checked in accordance with the requirements given

in chapters 7 and C of the IKC Publication 731. The infor­

mation was checked from the following documents supplied

with the dosimeters:

1. Instruction Manual for 2570A and 2570B Farmer Dose-

meter, Nuclear Enterprises (NE) Limited 1980.

2. Instruction Manual for 0-6 cc Ionization Chamber

(Guarded stem) Type 2571, NE Limited 1980.

3. Provisional Instructions for Use of Dosemeter IQ4,

12/83, Physikalisch-Technische werkstatten Dr.

Pychlay Gmbh, Freiburg.

The check results are marked on the following copies of the

relevant pages of IEC 731 using the notations:

+: information supplied

(+): information supplied, but not excactly as required

-: information not supplied

0: information not relevant or not checked.

731 S IEC 1982 - 3 1 -

6.3.7 For an exposure-rate meter, the check indication ai' be 31 jater than the minimum effective INDICATED VALUE.

6.3.3 A device snail be provided to block the apcrtL're when the IONIZATION CHAMBER is removed.

6.4 Repeatability

Requirement

The standard deviation of a singie measurement with :he check source as determined from repeated measurements shall not exceed 0.3"o iO."'''o) (~ee Sub-clauses AI.2.9 and 3.2).

Test method

Ten measurements shall be taken in the manner ipecified in the instructions for use. and the standard deviation calculated. With an overall -STABILITY CHECK DEVICE the chamber snail be completely removed from :he check device and replaced between successive measure­ments. The overail STABILITY CHECK DEVICE and -.he IONIZATION CHAMBER shall be as neariy at temperature equilibrium as possible, but corrections may be made for cnar.get :n air density if necessary.

". Markings

All .Tiarivinis and attached '.aceis snail be ;:ear end permanent.

".I C.J..r.l3EZ iSSE.MBLY

'...'. 7'ie '"oiiowing information -hail .;e clear:;, "narked jr. :he :HA:.15EA \S3EMBL'. .?: ;n a firmiv attached iabei:

— :he -er;ai number of :he je-.-ic::

— an Indication of whether the chamber is leaiec:

— a -.yarning that the CHAMBER ASSEMBLY shall not be used in contact with a patient if :t does not meet the requirements of Type 3. BF ar CF equipment as defined in I EC Publi­cation 601-1.

— if it has ACCESSIBLE CONDUCTIVE PARTS, a warning that it shall not be used in contact with a patient unless it is connected to a MEASURING ASSEMBLY which is designed so that the complete instrument meets the requirements of Type 3, BF or CF equipment as defined in IEC Publication 601-I.

(This may require the specification of particular models of MEASURING ASSEMBLIES.)

7.1.2 The following information should be clearly marked on the CHAMBER ASSEMBLY or on a firmly attached label:

— the manufacturer's name, trade mark or other recognized marking:

— the .ype number of the device.

7.1.3 The following information may be given by markings on the CHAMBER ASSEMBLY or on a firmiv attached label:

731 £ IEC 198: - 3 3 -

an engraved mark -o that the REFERENCE POINT o\ the chamber can be accurately posi­tioned during calibration:

the nominal tuil scaie reading when the chamber is supplied specifically for ase with one MEASURING ASSEMBLY (especially for a condenser chamber);

— the RATED RANGE o( radiation qualities.

7.2 MEASURING ASSEMBLY

7.2.i The following information snail be clearly marked on the MEASURING ASSEMBLY:

the manufacturer'i name. trade mark or other recognized marking;

the type number and serial number of ".he device:

the legend "'jncorrected" on or adjacent :o the display if this is scaled in radiation anus:

the function oi ;ach socuet. operating control ana indicator:

in :he case oi i multi-range instrument with an analogue display. :he range-char.ging controls snail be marked .vith the INDICATED -'ALL'E at :'ui!--caie for each position.

Range-changing controls .snail not be marked .vith scaie muitioiyins factors:

3 3 - a warning that x JHAMBER ASSEMBLY connected :o the MEASURING \SSEMBL-: ir.ai! not be used in contact ••vith a patient, if the MEASURING AEEEMBLY S not aesignec; tc mes: :r>; requirements of Type 3. 3F or C? .'ouirrr.er.t is defined in 'EC P'.iCiicaticn ->0i-!:

0 3 — if :he MEASURING ASSEMBLY meets the requirements of Type 3. 3F or CF equipment as defined in IEC Publication601-!. an indication of Types jr mcdeis oi CHAMBER ASSEMBLY with which the MEASURING ASSEMBLY makes i complete instrument which also meets these requirements, and a warning that a CHAMBER ASSEMBLY connected to this MEASURING ASSEMBLY shall not be used in contact with a patient, if the complete instrument does not meet these requirements:

Y g — the mains voltpges and frequencies for which it is designed.

0 + 7.2.2 If the MEASURING ASSEMBLY is supplied with more than one chamber, the chambers may be identified by markings on the MEASURING ASSEMBLY.

+ + 7.2.3 Ifgraphical symbols are used they should be those given in Appendix D

7.3 STABILITY CHECK O E VICE

7.3.1 The following information shall be clearly marked on the STABILITY CHECK DEVICE:

•t- - — the manufacturer's name, trade mark or other recognized marking;

+ +. — thetypenumber and serial number of the device.

0 0

:3 J

731 ^ I EC 1982 - i f -

7.3.2 For a device using a radioactive source, a ?-.. :::i. r !ac-.i ahail be affixed to the surface of the shielded container and. if the device is scire:: r. :lv pan M the MEASURING ASSEMBLY, on the surface of the control panel, and on the surfac? of the carrying case, if one is supplied. This label shall include the international trefoil ymool and should include the name of the radionuclide, the activity of the radionuclide md :oe date for which the stated activity is applicable.

7.3.3 If any part of the device which contributes to protection against ionizing radiation has to be detached in order to insert the chamber. th;s part -snail bear a warning about the loss of protection and the necessity for replacing It after .he .-ceding.

3. Instructions for use

The instructions for use are considerea to ne par: of "he accompanying documents.

8.! General

- - 8.1.' In order to ensure correct use of the -.nstru—ent. a manual jf instructions, for use :nail ?e _ - provided. M e a s u r i n g asse i ruc l" ' ' , l o - i r a i i c t t c i . a r i e r - '

0 J 8.1.2 This manual should compiy in genera: *'.:?. "he requirements contained in iEC Rusti­cation 2" 3: Documentation to be Suopiie-a ••.::.-. Electronic Measuring Apparatus.

- - 8.1.3 Sufficient information -hail be gi'. er. n t.-.c :n;truc::or.s 'or use to ensure unumricuous icen tin cat; en of trie instrument to which :::e- :.r *•'.'..

0 0 3.1.- All warning; ano essential requirement; •.-.•:_:c: ".• .vritten r. '.he .ernacuiar :f".ne nurcr.aser or :n a language mutually agreed between thr — anuf.icturer anc the purchaser.

- - 8.1.3 For the ME XSL RING \S3EM3LV. ' each . 'Os ;Z. iTi i ; \ C H ^ M 3 E a ' J n d each iTiBILITY CHECtN

- - DEViC2rir.forn.uucn shall be supplied on construction, metnod of operation and specified performance.

0 J 8.1.6 If the instrument is claimed to compiy with the requirements o( this standard, it snail be stated whether the instrument ior component if supplied separately) is a REFERENCECLASS ora FIELD-::..\ss INSTRUMENT.

0 0 S.I.7 For an instrument intended to operate under special conditions and which does not fuifii JII the requirements of this standard, information shall be provided about those clauses with which it does not comply.

0 0 8.1.3 For an instrument incorporating a cable-connected small thtmble chamber, which does not meet the requirements of Type B. BF or CF equipment as defined in IEC Publication 601-1. a warning shall be given that th.e instrument snail not be used in contact with a patient.

8.2 Specified performance - General paints

0 0 S.2.1 Data derived from TYPE TESTS shall be given in the instructions for use. even if also given in test sheets.

731 £ I EC 1982 - 3 7 -

0 O S.2.2 Data derived from individual tests may be given in the instructions for use. but if they are not, then reference should be made to appropriate test sheets.

8.3 CHAMBER ASSEMBLY

8.3.! Construction

The following information shail be provided:

- +• ai the size and shape of the IONIZATION CHAMBER, both internal and external:

_ + bi the thickness, density and material of the IONIZATION CHAMBER wail:

_ _ c, the electrical connections between each internal conducting part of the CHAMBER

ASSEMBLY and the cable connector:

- -r d\ the dimensions and material of the buiid-'ipc-p. if any;

- - a the position of the REFERENCE POINT jf:r.s IONIZATION CHAMBER in relation :o a recog­

nizable point (e.g. :he tip o\ a thimbie chamber •• or a mark;

- + / ; whether the IONIZATION CHAMBER is guarded or unguarded:

- - g, whether the IONIZATION CHAMBER is sea:;a or unsealed.

S.3.2 Method or 'operation

The following information shail be prc ice i :

0 0 a. for a CHAMBER \SSEM3LY supplied independently of MEASURING ASSEMBLY, guidance about the type of MEASURING ASSEMBLY for which it is suitable and about :he method of connection, anci a warning if a current-:irr.:t:r.g resistor is necessary:

- - b' appropriate methods of suoporting the CHAMBER ASSEMBLY, and a .varning about inap­propriate methods:

- r c: whether the chamber is suitable for usein a phantom:

- +• d) the recommended orientation in the useful beam and information about the dependence of

RESPONSE on orientation in the useful beam:

.*. * e: the RATED RANGE of polarizing voltages:

_ +. f) the maximum polarizing voltaae that may be applied without damaae and without charge multiplication:

g; guidance about the time to be allowed before making a measurement after the chamber has been subjected to the following:

+• + — switching-on of polarizing voltage: - + — connection of electrical fittings; - - — movement of cable; _ _ — sudden change of pressure or temperature: +• - — effects of transport.

- - hi recommended methods of checking that the RESPONSE is not being affected by stray radi­ation or external fields;

- - i) a warning that frequent checking with a STABILITY CHECK DEVICE is advisable, especially for a sealed IONIZATION CHAMBER;

731 % [EC 1982 - 8 9 -

- ( - ) k; a warning where applicable that long exposure to high humidity may have an adverse effect:

- + /) recommended methods oi correcting the INDICATED VALUE of unseaied chambers for

changes in air density;

- - m / permissible methods of cleaning the CHAMBER ASSEMBLY:

- T ni a warning against damaging fragile parts, for exampie the window of thin-window chambers;

- + ot the type of radioactive STABILITY CHECK DEVICE (if any) to be used with the dosimeter:

- ( - ) pi a warning that leakage currenis should be checked.

S.3.J Specified performance

Data derived from TYPE TESTS on any of :he following INFLUENCE QUANTITIES, about the:r RATED RANGE and the VARIATION of RESPONSE and leakage current within the RATED RANGE shall be provtded:

- +• a: radiation quaiity:

- - hi field size:

- - i.\ iourc2-;hamber distance :;:-.der jonsideration):

- - j : exposure rate:

O G • isposure i for a condenser cr.ambsrt:

- - / ' temperature:

- _ j humidity:

- - hi long-term stability of 3E3POVSE.

S.-i .V/E.;S'IR/.VC ISSEUBL-

3.4.1 Canaruciion

Tne following information snail be provided:

0 T- at number and types of batteries required:

- 0 b> type and rating of fuses required:

1 ) - •* c; potential differences from earth of the polarizing suppiv'and the zuard terminal; 2) - -

- + d) if access to the inside is permitted, a circuit diagram with layout, and the means of access:

- 0 ei ifaccess to the inside is not permitted, a warning to this effect:

+ + f) whether the MEASURING ASSEMBLY is sealed against the effect of high humidity;

- * g> method of maintaining desiccator.

8.4.2 Method of operation

The following information shall be supplied:

731 £ 1EC 1982 -91 -

0 a; for a mains-powered instrument, the RATED RANGE of mains voltages and frequencier.

0

0 b) means of adjusting instrument to accept the mains voltage available:

+ o for a battery-powered instrument, the method of testing whether the batteries need replacing and the method of replacement:

+• d) the function and method of operation of each control, the purpose of each socket anri the meaning of each indication:

•r e) the correct operating position of the MEASURING ASSEMBLY and the necessity for. and method of levelling;

f) guidance on the time to be allowed, before making a measurement after the MEASURING ASSEMBLY has been subjected to the following:

— switching on ISTABIUZATION TIME-:, — connection of electrical fittings, — sudden changes of temperature or humidity, — effects ot transport:

g; recommended methods of checking that the RESPONSE is not being affected by high humidity, stray radiation or external fieids:

+• hi guidance about suitable types of associated IONIZATION CHAMBERS, and types of piugs required:

*'/ the \ ilue of any limiting resistor in :he polarizing voltage supply, or a .varning if such a resisior is not incorporated:

k. for a MEASURING ASSEMBLY that has a scale narked in radiation units, a '.varning icout the need to appiy CALIBRATION FACTORS :o the INDICATED VALUES.

8.4.J Specified performance

Information derived from TYPE TESTS shall be provided about the following points jniess it is provided in accompanying test sheets:

+• ai the RESOLUTION of the display device:

6; the repeatability of successive measurements:

+ c; EFFECTIVE RANGE:

+ d) NON-LINEARITY;

+ t/ uncertainty of range changing;

0 f) RESPONSE TIME (of an exposure-rate meter);

gj for exposure meters the RATED RANGE of input currents or exposure rates and the VARIATION of RESPONSE in the RATED RANGE;

h) the RATED RANGE of temperature and humidity and the VARIATION of RESPONSE and of

ZERO-DRIFT and ZERO-SHIFT in the RATED RANGES;

+• i) expected useful life of specified batteries, in use and in storage:'

0 k) VARiArlONof RESPONSE in the RATED RANGE of mains voltage;

+ I) expected long-term stability.

731 S I EC 198: - 9 i -

8.5 Electrical STABILITY CHECK OEVIC*

Information shall be provided on the method of operation and the repeatability to be expected when it is operated in accordance with the instructions for use.

8.6 Radioactive STABILITY CHECK DEVICE

8.6.1 Construction

Information shall be provided about the construction of the device, the strength and type of sourcets) 3nd the exposure rate at 2 cm or 10cm from the surface cf the housing so that suitable precautions can be taken for storage and in case of mechanical damage or fire.

8.6.2 Method of operation

- ) For an overall STABILITY CHECK DEVICE, instructions shall be provided on the correct

positioning of the IONIZATION CHAMBER and the method of" assessing the temperature at the position of the IONIZATION CHAMBER. Guidanc: should be given as to how often and in what manner the instrument should be checked, and what precautions have to be taken in order to achieve the specified performance. A warning shall te given not to leave the chamber in the radioactive STABILITY CHECK DEVICE for unnecessary long periods of time, if this is likely to have an adverse effect on the performance of the chamber.

3.6. J Specified performance

Information snail be given on the repeatability to be expected when the device is operated in accordance with the instructions for use.

9. Test sheets

The test sheets are considered to be part of the accompanying documents.

9.! General

9.1.1 If an instrument is supplied by the manufacturer with a calibration, test sheets shall be provided giving CALIBRATION, and CORRECTION FACTORS by which the INDICATED VALUE

of the instrument (or the RESPONSE of the IONIZATION CHAMBER) may be corrected to give the exposure or exposure rate it the REFERENCE POINT of the chamber.

9.1.2 If an instrument is supplied without a calibration, information about CALIBRATION and CORRECTION FACTORS of a typical instrument shall be provided either in the instructions for use or on separate test sheets.

9.1.3 It shall be slated on each test sheet whether the data have been derived from a TYPE TEST or a ROUTINE TEST.

9.2 Calibration conditions

9.2.1 If CALIBRATION FACTORS are provided by the manufacturer they shall be given over the RATED RANGE of radiation qualities; alternatively the range of radiation qualities shall be given for which the CALIBRATION FACTORS fail within stated limits.

Säteilyturvakeskus Strälsäkerhetscentralen Finnish Centre for Radiation and Nuclear Safety

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