ISO 15568:1998
(Main)Practice for use of calorimetric dosimetry systems for electron beam dose measurements and dosimeter calibrations
Practice for use of calorimetric dosimetry systems for electron beam dose measurements and dosimeter calibrations
Pratique de l'utilisation de systèmes dosimétriques calorimétriques pour des mesures de dose délivrée par un faisceau d'électrons et l'étalonnage de dosimètres
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Standards Content (Sample)
INTERNATIONAL
IS0
STANDARD
15568
First edition
1998-12-15
Practice for use of calorimetric dosimetry
systems for electron beam dose
measurements and dosimeter calibrations
Pra tique de l’u tilisa tion de sys tkmes dosim6 triques calorimk triques pour des
mesures de dose dglivrke par un faisceau d ’klectrons et Malonnage de
dosimk tres
Reference number
--
IS0 15568: 1998(E)
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IS0 15568:1998(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies
(IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. IS0 collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
International Standard IS0 15568 was prepared by the American Society for Testing and Materials (ASTM)
Subcommittee E10.01 (as E 1631-96) and was adopted, under a special “fast-track procedure ”, by Technical
Committee ISO/TC 85, Nuclear energy, in parallel with its approval by the IS0 member bodies.
A new ISO/TC 85 Working Group WG 3, High-level dosimetry for radiation processing, was formed to review the
voting comments from the IS0 “Fast-track procedure” and to maintain these standards. The USA holds the
convenership of this working group.
International Standard IS0 15568 is one of 20 standards developed and published by ASTM. The 20 fast-tracked
standards and their associated ASTM designations are listed below:
IS0 Designation ASTM Designation Title
15554 E 1204-93 Practice for dosimetry in gamma irradiation facilities for food
processrng
15555 E 1205-93 Practice for use of a ceric-cerous sulfate dosimetry system
15556
E 1261-94 Guide for selection and calibration of dosimetry systems for
radiation processing
15557
E 1275-93 Practice for use of a radiochromic film dosimetry system
15558 E 1276-96 Practice for use of a polymethylmethacrylate dosimetry system
15559 E 1310-94 Practice for use of a radiochromic optical waveguide dosimetry
system
1400-95a
15560 E Practice for characterization and performance of a high-dose
radiation dosimetry calibration labora tory
15561 E 1401-96 Practice for use of a dichromate dosimetry system
0 IS0 1998
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 l CH-1211 Geneve 20 l Switzerland
Internet iso @ iso.ch
Printed in Switzerland
ii
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IS0 15568:1998(E)
as0
15562 E1431-91 Practice for dosimetry in electron and bremsstrahlung irradiation
facilities for food processing
E 1538-93 Practice for use of the ethanol-chlorobenzene dosimetry system
15563
15564 E 1539-93 Guide for use of radiation-sensitive indicators
E 1540-93 Practice for use of a radiochromic liquid dosimetry system
15565
15566 E 1607-94 Practice for use of the alanine-EPR dosimetry system
Practice for dosimetry in an X-ray (bremss tra hlung) facility for
15567 E 1608-94
radiation processing
Practice for use of calorimetric dosimetry systems for electron
15568 E1631-96
beam dose meas urements and dosimeter calibrations
Practice for dosimetry in an electron-beam facility for radiation
15569 E1649-94
processing at energies between 300 keV and 25 MeV
Practice for use of cellulose acetate dosimetry system
15570 E 1650-94
E 1702-95 Practice for dosimetry in a gamma irradia tion facility for radiation
15571
processing
E 1707-95 Guide for es tima ting uncertainties in dosimetry radiation
15572
processing
E 1818-96 Practice for dosimetry in an electron-beam facility for radiation
15573
processing at energies between 80 ke V and 300 ke V
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0 IS0 IS0 15568: 1998(E)
AhlERICAN SOCIETY FOR TESTING AND MATERIALS
Designation: E 1631 - 96 An American National Standard
100 Barr Harbor Dr., West Conshohocken, PA 19428
#Tb
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
If not listed in the current combined index, will appear in the next edition.
Standard Practice for
Use of Calorimetric Dosimetry Systems for Electron Beam
Dose Measurements and Dosimeter Calibrations’
This standard is issued under the fixed designation E 163 1; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (c) indicates an editorial change since the last revision or reapproval.
E 1649 Practice for Dosimetry in an Electron Beam
1. Scope
Facility for Radiation Processing at Energies Between
1.1 This practice covers the preparation and use of
300 keV and 25 MeV2
semi-adiabatic calorimeters for measurement of absorbed
E 1707 Guide for Estimating Uncertainties in Dosimetry
dose in graphite, water, or polystyrene when irradiated with
for Radiation Processing2
electrons. The calorimeters are either transported by a
2.2 International Commission on Radiation Units and
conveyor past a scanned electron beam or are stationary in a
Measurements (ICR U) Reports:3
broadened beam. It also covers the use of these calorimeters
ICRU Report 33 Radiation Quantities and Units
to calibrate dosimeter systems in electron beams intended for
ICRU Report 34 The Dosimetry of Pulsed Radiation
radiation processing applications.
ICRU Report 35 Radiation Dosimetry: Electron Beams
1.2 This practice applies to electron beams in the energy
with Energies Between 1 and 50 MeV
range from 4 to 12 MeV.
ICRU Report 37 Stopping Powers for Electrons and
1.3 The absorbed dose range depends on the absorbing
Positrons
material and the irradiation and measurement conditions.
ICRU Report 44 Tissue Substitutes in Radiation
Minimum dose is approximately 100 Gy and maximum
Dosimetry and Measurements
dose is approximately 50 kGy.
1.4 The averaged absorbed dose rate range shall generally
3. Terminology
be greater than 10 Gy l s-l, but depends on the same
3.1 Definitions:
conditions as above.
3.1.1 adiabatic, adj-no heat exchange with the sur-
1.5 The temperature range for use of these calorimeters
roundings.
depends on the thermal resistance of the materials and on
3.1.2 calorimeter, n-assembly consisting of calorimetric
the calibration range of the temperature sensor.
body (absorber), thermal insulation, and temperature sensor
1.6 This standard does not purport to address all of the
with wiring.
safety concerns, tf any, associated with its use. It is the
3.1.3 calorimetric body, n-the mass of material ab-
responsibility of the user of this standard to establish appro-
sorbing radiation energy and whose temperature is mea-
priate safety and health practices and determine the applica-
sured.
bility of regulatory limitations prior to use.
3.1.4 endothermic reaction, n-a chemical reaction that
consumes energy.
3.1.5 exothermic reaction, n-a chemical reaction that
2. Referenced Documents
releases energy.
2.1 ASTM Standards: 3.1.6 heat defect (thermal defect), n-the amount of
170 Terminology Relating to Radiation Measurements energy released or consumed by chemical reactions caused
and Dosimetry2 by the absorption of radiation energy.
666 Practice for Calculating Absorbed Dose from 3.1.7 specific heat capacity, n-the amount of energy
Gamma or X Radiation2 required to raise a specified mass of material by a specified
668 Practice for Application of Thermoluminescence- temperature.
3.1.8 thermistor, n-electrical resistor with a well-defined
Dosimetry (TLD) Systems for Determining Absorbed
relationship between resistance and temperature.
Dose in Radiation-Hardness Testing of Electronic
3.1.9 thermocouple, n-a junction of two metals pro-
Devices2
ducing an electrical voltage with a well-defined relationship
126 1 Guide for Selection and Calibration of Dosimetry
to temperature.
Systems for Radiation Processing’
3.2 For additional terms, see Terminology E 170 and
143 1 Practice for Dosimetry in Electron and Bremsstrah-
ICRU Report 33.
lung Irradiation Facilities for Food Processing2
4. Significance and Use
l This practice is under the jurisdiction of ASTM Committee E-10 on Nuclear
4.1 This practice is applicable to the standardization of
Technology and Applications and is the direct responsibility of Subcommittee
E1O.O1 on Dosimetry for Radiation Processing.
Current edition approved June 10, 1996. Published July 1996. Originally
3 Available from the Commission on Radiation Units and Measurements, 79 10
published as E 163 1 - 94. Last previous edition E 163 1 - 94.
Woodmont Ave., Suite 800, Bethesda, MD 208 14.
2 Annual Book of ASTM Standards, Vol 12.02.
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@ IS0
IS0 15568:1998(E)
exchange. The temperature drifts before and after irradiation
absorbed dose in electron beams, the qualification of elec-
are extrapolated to the midpoint of the irradiation period in
tron irradiation facilities, dosimetry intercomparisons be-
order to determine the true temperature increase due to the
tween laboratories, periodic checks of operating parameters
of electron processing facilities, and calibration of other absorption of radiation energy.
5.2 Heat dehct-Chemical reactions in irradiated water
dosimeters in electron beams.
and other materials (resulting in what is called the heat defect
NOTE l-For additional information of the use of dosimetry in
or thermal defect) may be endo- or exothermic and may lead
electron accelerator facilities, see Practices E 143 1 and E 1641, ICRU
to measurable temperature changes. They are respectively
Reports 34 an.d 35, and Refs 1-3.4
deficient or excessive with respect to the temperature in-
4.2 Graphite calorimeters provide a reliable means of
crease due directly to the absorption of radiation energy in
measuring absorbed dose in graphite, The dose measurement
the water. The extent of these effects depends on the purity
is based on the measurement of the temperature increase in a
or the gas content of the water and on any chemical effects
graphite absorber irradiated by an electron beam.
arising from the container of the water. At the absorbed
4.2.1 For graphite for which the specific heat capacity is
doses and dose rates usually encountered by these calorime-
known, no calibration of the graphite calorimeter is needed.
ters, these effects are not significant (3).
4.2.2 The absorbed dose in other materials irradiated
5.3 Temperature efects from accelerator structure-The
under equivalent conditions may be calculated. Procedures
calorimeters are often irradiated on a conveyor used for
for making such calculations are given in Practices E 666 and
passing products and samples past the irradiation zone.
E 668, Guide E 126 1, and Reference (1).
Radiated heat from the mechanical structures of the irradia-
4.2.3 The average absorbed dose in the graphite volume is
tion facility and from the conveyor may contribute to the
measured. Dose gradients may occur in this volume and may
measured temperature increase in the calorimeters.
have to be considered when estimating dose in other
5.4 Thermal equilibrium -The most reproducible results
materials.
are obtained when the calorimeters are in thermal equilib-
4.3 Water calorimeters provide a reliable means of mea-
rium before irradiation.
suring absorbed dose in water. The dose measurement is
5.5 Other materials-The temperature sensors, wires, etc.
based on the measurement of the temperature increase in a
of the calorimeter represent foreign materials, which may
volume of water, for example, a water-filled polystyrene petri
influence the total temperature rise. These components
dish.
should be as small as possible.
4.3.1 The response of the water calorimeters should be
5.6 Dose gradients- Dose gradients will exist within the
calibrated by comparison with graphite calorimeters irradi-
calorimetric body when it is irradiated with 4 to 12 MeV
ated under precisely the same conditions.
electrons. These gradients must be taken into account, for
4.3.2 The average dose in the water calorimeter is evalu-
when other dosimeters are calibrated by
example,
ated. Dose gradients may occur in this volume and may need
intercomparison with calorimeters.
to be considered when estimating dose in other materials.
4.4 Polystyrene calorimeters provide a reliable means of
measuring absorbed dose in polystyrene. The dose measure- 6. Apparatus
ment is based on the measurement of the temperature
6.1 One Type of Graphite Calorimeter, is a disc of graphite
increase in a volume of polystyrene.
placed in a thermally-insulating material such as foamed
4.4.1 The response of the polystyrene calorimeters should
plastic (6-8). A calibrated thermistor or thermocouple is
be calibrated by comparison with graphite calorimeters
embedded inside the disc. See Fig. 1 for an example of such
irradiated under precisely the same conditions.
a calorimeter. Some typical examples of graphite disc thick-
4.4.2 The average dose in the polystyrene volume is
nesses and masses are listed in Table 1 (2).
evaluated. Dose gradients may occur in this volume and may
6.2 A Typical Water Calorimeter, is a sealed polystyrene
need to be considered when estimating dose in other
petri dish filled with water and placed in thermally-insuiating
materials.
foamed plastic (6). A calibrated temperature sensor
4.4.3 Polymeric materials other than polystyrene may be
used for calorimetric measurements. Polystyrene is used
because it is known to be resistant to radiation (4) and
because no exo- or endothermic reactions are taking place
.
(5)
5. Interferences
1
5.1 Extrapolation -The calorimeter designs described in
33 cm
this practice are usually not strictly adiabatic, because of the
exchange of heat with the surroundings or within the
calorimeter assembly. The maximum temperature reached
by the calorimetric body is different from the temperature
that would have been reached in the absence of that heat
Front Virw
Sidr View
FIG. 1 Exam lple of a G lraphite Calorimeter Used at a IO-MeV
J The boldfaced numbers in parentheses refer to the list of references at the end
Industrial Electron Accelerator (7)
of this practice.
2
2
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IS0 15568: 1998(E)
TABLE 1 Thickness and Size of Several Graphite Calorimeters
disc placed in thermally-insulating foamed plastic. A cali-
Designed at NIST for Use at Specific Electron Energies
brated thermistor or thermocouple is imbedded inside the
Electron Range disc. The dimension of the polystyrene disc may be similar to
Calorimeter Disc (30 mm diameter)
Electron
in GraphiteA
that of the graphite and water calorimete&.
Thickness B
EnwY density: 1 :7 g *WI-~
Mass,
6.4 Radiation-resistant components should be used for
MeV
9
g cm-’
cl=+
the parts of the calorimeter that are exposed to the electron
0.84 5.9
4 2.32 1.36 0.49
beam. This also applies to insulation of electrical wires.5
5 2.91 1.71 1.05 0.62 7.5
6.5 Good thermal contact must exist between the temper-
6 3.40 2.05 1.25 0.74 8.9
ature sensor and the calorimetric body. For graphite and
0.97 11.7
0 4.59 2.70 1.65
10 5.66 3.33 2.04 1.20 14.4
polystyrene calorimeters, this can be assured by adding a
2.22 1.31 15.7
I1 6.17 3.63
small amount of heat-conducting compound when
16.9
12 6.68 3.93 2.40 1.41
mounting the temperature sensor.
A This is the continuous-slowing-down-approximation (CSDA) range r, of
6.6 Read-Out-The calorimeters are read by measuring
electrons for a broad beam incident on a semi-infinite absorber. It is calculated
the temperature of the calorimetric body. This temperature
from:
is registered by thermistors or thermocouples.
Eo ’
-*dE 6.6.1 Thermistor-Use a high-precision ohm-meter for
r, =
s
0 Wdtot
measurement of thermistor resistance. The meter should
where:
have a resolution of better than & 0.1 % and an accuracy of
= the primary electron energy, and
E*
better than =f= 0.2 %. It should preferably be equipped for
= the total mass stopping power at a given electron energy (1).
(S/P) et
four-wire type resistance measurements, especially if the
* The thicknesses specified are equal to 0.36 (rd.
thermistor resistance is less than 10 kS2. With the four-wire
measurement technique, the effects of resistance in the
(thermistor) is placed through the side of the dish into the
measurement wires and electrical contacts are minimized.
water. See Fig. 2 as an example of such a calorimeter.
6.6.2 Other appropriate instrumentation may be used for
6.3 A Typical Polystyrene Calorimeter, is a polystyrene
the thermistor resistance measurement, for example, a resis-
tance bridge or commercial calibrated thermistor readers (7).
Thormislor
It is important for both ohm-meters and resistance bridge
measurements to minimize the dissipated power in the
thermistor, preferably below 0.1 mW.
?C\
6.6.3 Thermocouple-Use a high-precision digital volt-
meter, or commercial reader (2). The sensitivity of the
voltmeter should be better than 0.1 pV.
7. Calibration Procedures
7.1 The graphite calorimeters may be considered either as
primary standard dosimetry systems or as routine dosimetry
systems requiring calibration against other standards, de-
pending on how they are used for dose measurement, while
water and polystyrene calorimeters typically are used as
routine dosimeters.
7.2 Primary Standard Dosimeter-In order to consider
the graphite calorimeter as a primary standard dosimeter, the
specific heat capacity of the graphite and its temperature
dependence must be known and the temperature sensors and
the measuring equipment must be accurately calibrated. Any
I- ElrctricaI~r*ctors 1
influence of the irradiation conditions must be evaluated and
any possible influence on the uncertainty of the dose reading
Vlaw 8-9
must be taken into account.
7.2.1 The specific heat capacity of the graphite of the
calorimetric body and its functional dependence on temper-
ature may be determined by several techniques. One method
employs a built-in electrical heater in the calorimetric body
to dissipate a known amount of electrical energy (see 7.2.3
and Appendix Xl). Another method uses a separate adia-
batic calorimeter to measure specific heat of a sample of the
graphite material (8). Adiabatic calorimeters that use differ-
ential scanning calorimetry techniques for specific heat
FIG. 2 Example of a Water Calorimeter Used for Routine s Radiation resistant wiring is available, for example, from Hubcr und Suhner,
Measurements at a IO-MeV Industrial Electron Accelerator (6) IQfGkon, Switzerland, under the brand name Radox.
3
3
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IS0 15568: 1998(E)
0 IS0
dsTE, E 1631
a routine dosimeter. Its response shall be calibrated against
measurement are commercially available.
another reference standard dosimeter.
7.2.2 Calibrate the temperature sensors and their associ-
ated readout instrumentation by placing the sensors in a 7.3.1 Calibration may be obtained in two ways:
well-controlled environment with a precision, high-accuracy 7.3.1.1 Irradiation at a calibration laboratory together
with reference standard dosimeters.
thermometer whose response is traceable to national stan-
7.3.1.2 Irradiation at the user ’s facility together with
dards. If possible, place the entire calorimetric body con-
taining the temperature sensors in this environment in good transfer standard dosimeters from a calibration laboratory.
thermal contact with the calibration thermometer, An appro- 7.3.2 For irradiation in a calibration laboratory, usually
priate environment could be a stirred oil or water bath or a the procedure in 8.3 may be used. Any effect on the
calorimeter response in changing from the calibration labo-
well-insulated metal block, Slowly vary the temperature of
ratory to the user ’s facility must be evaluated and taken into
the environment over the range of expected use, allowing
ample time for all components to come to thermal equilib- account.
7.3.3 For irradiation together with transfer dosimeters at
rium. Record the temperature sensor readings as a function
of the calibration thermometer readings. the user ’s facility, the procedure given in Section 9 may be
7.2.3 If the specific heat capacity of the graphite is not used.
7.4 Water or polystyrene calorimeters may be calibrated
known or cannot be obtained conveniently, then the calori-
against graphite calorimeters or by comparison with transfer
metric body may be equipped with a built-in electrical heater
standard dosimeters from an accredited calibration labora-
for calibration. This, in effect, determines the mean specific
tory by irradiation sequentially (or simultaneously) at an
heat capacity for a particular initial temperature and temper-
electron accelerator. The radiation field over the cross-
ature increase.
7.2.3.1 The heater may consist of a resistance wire that is sectional area of the calorimetric body shall be uniform to
placed in the graphite calorimetric body in such a way that within t 2 % and constant over the time required to
its heat is dissipated evenly in the graphite disc. The mass of irradiate both calorimeters. The irradiation conditions
the heater wire inside the graphite disc should be only a small should be arranged so that the electron fluence is equal in the
fraction of the total mass of the two combined, preferably two calorimeters. If that is not the case, corrections or
less than 1 %. adjustments must be made.
7.2.3.2 A known amount of energy is dissipated in the 7.4.1 The specific heat capacity of polystyrene is a func-
graphite disc if a known electrical current, 1, (unit: A) is tion of temperature. The calibration must therefore be
allowed to flow for a known time, t, (unit: s) through the wire carried out at a range of temperatures, so that a relationship
with resistance R (unit: ohm). The mean specific heat between the calibration factor (expressed in kGy l “C-l) and
Capacity, CG, may be calculated from the average temperature of the calorimetric body can be
determined.
12*R*t
7.4.2 The calibration factor for water calorimeters is
(1)
= K (Jekg- ‘*“C-*)
CG
approximately 3.4 kGy l “C-l and for polystyrene calorime-
ters it is approximately 1.4 kGy l OCL1. For graphite, the
where:
relationship is approximately 0.75 kGy 0 “C-l (see Note 2).
AT = the observed temperature (unit: “C) increase from the
These values apply for 10 MeV irradiation of calorimeters
initial temperature, TO to the maximum temperature,
with thickness approximately 1.7 g. cm-*.
T
ma9 and
7.5 Calibration of all types of calorimeters used as routine
??I = the mass (unit: kg) of the graphite disc.
dosimeters should be checked by comparison with reference
Only the resistance wire which is actually inside the graphite
standard or transfer standard dosimeters at a frequency
disc should be considered when determining the resistance
determined by the user.
R. The mean specific heat capacity determined is valid only
for the particular values of TO and Tmax employed. Thus; a
8. Dose Measurement Procedures
series of electrical calibrations are needed to cover the
expected temperature ranges of operation.
8 o i Conveyor Irradiation- For calorimeters carried on
7.2.3.3 To determine AT, plot the temperature versus
conveyors past scanned electron beams, the calorimeter is
time before and after switching on the electrical current.
usually disconnected from the temperature measurement
Extrapolate the curves to the midpoint of the heating time.
system just prior to irradiation and reconnected for readout
The two values of temperature obtained from the extrapola-
just after irradiation (9).
tions are used to calculate AT = T, - T, that would occur in
8.1.1 Before irradiation, measure the temperature of the
the absence of heat exchange with the surroundings.
calorimetric body and check that the temperature remains
7.2.4 If the specific heat capacity is determined by other
stable for a period of at least ten min (typically less than
means, then it shall be known over the expected temperature
0.1 OC change).
range of operation.
81.2 Disconnect the measurement wires and place the
calorimeter on the conveyor for transport through the
NOTE 2-Repeated measurements of specific heat of various types of
graphite have been carried out over the r&ge of 0 to 5O ’C, indicating a irradiation zone,
value for cG of 644.2 + 2.86. T (J kg-lX- ‘), where T is the mean 8.1.3 Transport the calorimeter through the irradiation
temperature ( ‘C) of the graphite, This value must, however, not be
zone on the conveyor system.
considered a universal value. (8).
8.1.4 During irradiation, record the time of irradiation,
and the irradiation parameters (electron energy, electron
7.3 Routine Dosimeter-Without knowledge of the spe-
current, scanned beam width, and conveyor speed).
cific heat of graphite, the graphite calorimeter may be used as
4
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0 IS0 IS0 45568:1998(E)
8.1.5 After passage of the irradiation zone, reconnect the been found to be the case for graphite and water, bi-~t not for
aluminum and water (2).
wires for measurement of temperature, and record the time
8.1.10 For the water and polystyrene calorimeters, mul-
from the end of irradiation to the first temperature measure-
tiply the temperature difference, T2 - T,, by the calibration
ment. Record the temperature as a function of time for 10 to
factor previously determined by calibration against graphite
20 min after irradiation, enough to establish the thermal
calorimeters (see Section 7), to evaluate the average absorbed
decay characteristics of the calorimeter.
dose in water or polystyrene, respectively.
8.1.6 Plot the temperature values as a function of time
8. I. 11 For well-established, reproducible irradiation con-
before and after irradiation.
ditions the extrapolation procedure of 8.1.7 may not be
8.1.7 Extrapolate the curves before and after irradiation to
needed. One measurement of temperature before and one
the midpoint of the irradiation time. The two values of
after irradiation may suffice, and the temperature difference
temperature obtained from the extrapolations are used as the
at the time of irradiation is found by use of a correction
temperature before irradiation ( T1) and after irradiation ( T2)
factor derived during the establishment of the irradiation
that would occur in the absence of heat exchange with the
procedures (6, 7, 9, 10).
surroundings. An example of data obtained by this measure-
8.2 On-line Irradiation on Conveyor-It is possible to
ment technique is shown in Fig. 3.
measure the calorimeters’ temperature during irradiation as
8.1.8 For the graphite calorimeter, the average absorbed
the calorimeters are transported through the irradiation zone
dose in the graphite disc, DG, is given by:
on the conveyor with measurement wires attached. Four-
= CG'(T2 - T,)
(2)
6), wire measurement (see 6.6.1) may be preferred in order to
increase measurement precision.
where:
8.3 Stationary Irradiation- The calorimeters described in
= the specific heat capacity of the graphite at the mean
CG
this practice may also be used in a stationary configuration
temperature during irradiation, (T, + T2)/2.
instead of being transported on a conveyor system through
8.1.9 The dose, DM, in another material of the same
the electron beam. In this arrangement the beam is made
dimensions irradiated under the same conditions is given by:
uniform over the area of the calorimeter disc either by the
DM=
DG*sM/sG (3)
use of metallic scattering foils or by raster scanning. The
. -
where: irradiation period is controlled by turning the electron beam
SM and A& = mass collision stopping powers of the other on and off.
material and graphite, respectively (see Guide E. 126 1 and 8.3.1 The readout of the temperature of the calorimeters
.’ .
ICRU Reports 37 and 44). in a stationary configuration may be done during irradiation
rather than measuring before and after irradiation as de-
8.1.9.1 This equation is valid only when the electron
scribed in 8.1.
fluences in the two absorbers of interest are equal, which has
8.3.2 With the electron beam turned off, locate the
I
calorimeter on the beam axis at an appropriate distance from
the accelerator beam exit window such that the beam profile
is uniform to within & 2 % across the diameter of the
calorimeter disc. The beam profile should be measured and if
Dose : 9.9 kGy
it varies more than rf= 2 % across the calorimeters, correc-
.
. AT : 12.3 “c
3. tions for the non-uniformity may have to be carried out.
3 001
Connect the temperature sensor wires to the calorimeter.
The temperature readout system is located outside of the
irradiation area, and the long connecting wires make four-
wire m
...
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