ISO/ASTM 51631:2002
(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
ISO/ASTM 51631 covers the preparation and use of semi-adiabatic calorimeters for measurement of absorbed doses in graphite, water or polystyrene when irradiated with electrons. The calorimeters are either transported by a conveyor past a scanned electron beam or are stationary in a broadened beam. It also covers the use of these calorimeters to calibrate dosimeter systems in electron beams intended for radiation processing applications. This International Standard applies to electron beams in the energy range from 4 MeV to 12 MeV. The absorbed dose range depends on the absorbing material and the irradiation and measurement conditions. The minimum dose is approximately 100 Gy and maximum dose is approximately 50 kGy. The averaged absorbed dose rate range shall generally be greater than 10 Gy·s-1 , but depends on the same conditions as above. The temperature range for use of these calorimeters depends on the thermal resistance of the materials and on the calibration range of the temperature sensor.
Pratique de l'utilisation des systèmes dosimétriques calorimétriques pour des mesures de dose délivrée par un faisceau d'électrons et pour l'étalonnage de dosimètres
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Standards Content (Sample)
INTERNATIONAL ISO/ASTM
STANDARD 51631
First edition
2002-03-15
Practice for use of calorimetric dosimetry
systems for electron beam dose
measurements and dosimeter
calibrations
Pratique de l’utilisation des systèmes dosimétriques
calorimétriques pour des mesures de dose délivrée par un
faisceau d’électrons et pour l’étalonnage de dosimètres
Reference number
ISO/ASTM 51631:2002(E)
© ISO/ASTM International 2002
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ISO/ASTM 51631:2002(E)
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ISO/ASTM 51631:2002(E)
Contents Page
1 Scope . 1
2 Referenced documents . 1
3 Terminology . 1
4 Significance and use . 2
5 Interferences . 2
6 Apparatus . 2
7 Calibration procedures . 3
8 Dose measurement procedures . 4
9 Calibration of other dosimeters . 6
10 Documentation . 6
11 Measurement uncertainty . 6
12 Keywords . 7
Annexes . 8
Bibliography . 9
Figure 1 Example of a graphite calorimeter used at a 10–MeV industrial electron accelerator . 3
Figure 2 Example of a water calorimeter used for routine measurements at a 10–MeV industrial
electron accelerator . 3
Figure3 Example of measurements of t emperature of a graphite calorimeter before and after
irradiation only . 5
Figure 4 Example of on-line measurements of a graphite calorimeter . 6
Table 1 Thickness and size of several graphite calorimeters designed at NIST for use at specific
electron energies . 3
Table 2 Factors contributing to uncertainties in the absorbed dose reading of the NIST Reference
Graphite Calorimeter . 7
Table 3 Factors contributing to uncertainties in the absorbed dose reading of routine polystyrene
calorimeters from Risø High Dose Reference Laboratory . 7
© ISO/ASTM International 2002 – All rights reserved iii
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ISO/ASTM 51631:2002(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
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. ISO 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.
ASTM International is one of the world’s largest voluntary standards development organizations with global
participation from affected stakeholders. ASTM technical committees follow rigorous due process balloting
procedures.
A pilot project between ISO and ASTM International has been formed to develop and maintain a group of
ISO/ASTM radiation processing dosimetry standards. Under this pilot project, ASTM Subcommittee E10.01,
Dosimetry for Radiation Processing, is responsible for the development and maintenance of these dosimetry
standards with unrestricted participation and input from appropriate ISO member bodies.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. Neither ISO nor ASTM International shall be held responsible for identifying any or all such
patent rights.
International Standard ISO/ASTM 51631 was developed by ASTM Committee E10, Nuclear Technology and
Applications, through Subcommittee E10.01, and by Technical Committee ISO/TC 85, Nuclear Energy.
Annexes A1 and A2 of this International Standard are for information only.
iv © ISO/ASTM International 2002 – All rights reserved
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ISO/ASTM 51631:2002(E)
Standard Practice for
Use of Calorimetric Dosimetry Systems for Electron Beam
1
Dose Measurements and Dosimeter Calibrations
This standard is issued under the fixed designation ISO/ASTM 51631; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision.
1. Scope Dosimetry (TLD) Systems for Determining Absorbed Dose
2
in Radiation-Hardness Testing of Electronic Devices
1.1 This practice covers the preparation and use of semi-
2.2 ISO/ASTM Standards:
adiabatic calorimeters for measurement of absorbed dose in
51261 Guide for Selection and Calibration of Dosimetry
graphite, water, or polystyrene when irradiated with electrons.
2
Systems for Radiation Processing
The calorimeters are either transported by a conveyor past a
51431 Practice for Dosimetry in Electron and Bremsstrahl-
scanned electron beam or are stationary in a broadened beam.
2
ung Irradiation Facilities for Food Processing
It also covers the use of these calorimeters to calibrate
51649 Practice for Dosimetry in an Electron Beam Facility
dosimeter systems in electron beams intended for radiation
for Radiation Processing at Energies Between 300 keV
processing applications.
2
and 25 MeV
1.2 This practice applies to electron beams in the energy
51707 Guide for Estimating Uncertainties in Dosimetry for
range from 4 to 12 MeV.
2
Radiation Processing
1.3 The absorbed dose range depends on the absorbing
2.3 International Commission on Radiation Units and
material and the irradiation and measurement conditions.
4
Measurements (ICRU) Reports:
Minimum dose is approximately 100 Gy and maximum dose is
ICRU Report 34 The Dosimetry of Pulsed Radiation
approximately 50 kGy.
ICRU Report 35 Radiation Dosimetry: Electron Beams with
1.4 The averaged absorbed dose rate range shall generally
−1
Energies Between 1 and 50 MeV
be greater than 10 Gy·s , but depends on the same conditions
ICRU Report 37 Stopping Powers for Electrons and
as above.
Positrons
1.5 The temperature range for use of these calorimeters
ICRU Report 44 Tissue Substitutes in Radiation Dosimetry
depends on the thermal resistance of the materials and on the
and Measurements
calibration range of the temperature sensor.
ICRU Report 60 Radiation Quantities and Units
1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3. Terminology
responsibility of the user of this standard to establish appro-
3.1 Definitions:
priate safety and health practices and determine the applica-
3.1.1 adiabatic—no heat exchange with the surroundings.
bility of regulatory limitations prior to use.
3.1.2 calorimeter—assembly consisting of calorimetric
2. Referenced Documents body (absorber), thermal insulation, and temperature sensor
with wiring.
2.1 ASTM Standards:
3.1.3 calorimetric body—the mass of material absorbing
E 170 Terminology Relating to Radiation Measurements
2
radiation energy and whose temperature is measured.
and Dosimetry
3.1.4 endothermic reaction—a chemical reaction that con-
E 177 Practice for the Use of the Terms Precision and Bias
3
sumes energy.
in ASTM Test Methods
3
3.1.5 exothermic reaction—a chemical reaction that re-
E 456 Terminology Relating to Quality and Statistics
leases energy.
E 666 Practice for Calculating Absorbed Dose from Gamma
2
3.1.6 heat defect (thermal defect)—the amount of energy
or X Radiation
released or consumed by chemical reactions caused by the
E 668 Practice for Application of Thermoluminescence-
absorption of radiation energy.
3.1.7 specific heat capacity—the amount of energy required
1 to raise a specified mass of material by a specified temperature.
This practice is under the jurisdiction of ASTM Committee E10 on Nuclear
Technology and Applicationsand is the direct responsibility of Subcommittee 3.1.8 thermistor—electrical resistor with a well-defined re-
E10.01on Dosimetry for Radiation Processing, and is also under the jurisdiction of
lationship between resistance and temperature.
ISO/TC 85/WG 3.
3.1.9 thermocouple—a junction of two metals producing an
Current edition approved Jan. 22, 2002. Published March 2002. Originally
e1
electrical voltage with a well-defined relationship to tempera-
published as E 1631 – 94. Last previous ASTM edition E 1631 – 96 . ASTM
e1
E1631–96 was adopted by ISO in 1998 with the intermediate designation ISO
ture.
15568:1998(E). The present International Standard ISO/ASTM 51631:2002(E) is a
revision of ISO 15568.
2
4
Annual Book of ASTM Standards, Vol 12.02.
Available from the Commission on Radiation Units and Measurements, 7910
3
Annual Book of ASTM Standards, Vol 14.02.
Woodmont Ave., Suite 800, Bethesda, MD 20814, U.S.A.
© ISO/ASTM International 2002 – All rights reserved
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ISO/ASTM 51631:2002(E)
3.2 For additional terms, see ASTM Terminology E 170 and exchange of heat with the surroundings or within the calorim-
ICRU Report 60. eter assembly. The maximum temperature reached by the
calorimetric body is different from the temperature that would
4. Significance and Use
have been reached in the absence of that heat exchange. The
4.1 This practice is applicable to the standardization of
temperature drifts before and after irradiation are extrapolated
absorbed dose in electron beams, the qualification of electron
to the midpoint of the irradiation period in order to determine
irradiation facilities, dosimetry intercomparisons between
the true temperature increase due to the absorption of radiation
laboratories, periodic checks of operating parameters of elec-
energy.
tron processing facilities, and calibration of other dosimeters in
5.2 Heat defect—Chemical reactions in irradiated water and
electron beams.
other materials (resulting in what is called the heat defect or
thermal defect) may be endo- or exothermic and may lead to
NOTE 1—For additional information of the use of dosimetry in electron
measurable temperature changes. They are respectively defi-
accelerator facilities, see ISO/ASTM Practices 51431 and 51649, and
5
cient or excessive with respect to the temperature increase due
ICRU Reports 34 and 35, and Refs 1-3.
directly to the absorption of radiation energy in the water. The
4.2 Graphite calorimeters provide a reliable means of mea-
extent of these effects depends on the purity or the gas content
suring absorbed dose in graphite. The dose measurement is
of the water and on any chemical effects arising from the
based on the measurement of the temperature increase in a
container of the water. At the absorbed doses and dose rates
graphite absorber irradiated by an electron beam.
usually encountered by these calorimeters, these effects are not
4.2.1 For graphite for which the specific heat capacity is
significant (3).
known, no calibration of the graphite calorimeter is needed.
5.3 Temperature effects from accelerator structure—The
4.2.2 The absorbed dose in other materials irradiated under
calorimeters are often irradiated on a conveyor used for passing
equivalent conditions may be calculated. Procedures for mak-
products and samples past the irradiation zone. Radiated heat
ing such calculations are given in ASTM Practices E 666 and
from the mechanical structures of the irradiation facility and
E 668, ISO/ASTM Guide 51261, and Ref (1).
from the conveyor may contribute to the measured temperature
4.2.3 The average absorbed dose in the graphite volume is
increase in the calorimeters.
measured. Dose gradients may occur in this volume and may
5.4 Thermal equilibrium—The most reproducible results
have to be considered when estimating dose in other materials.
are obtained when the calorimeters are in thermal equilibrium
4.3 Water calorimeters provide a reliable means of measur-
before irradiation.
ing absorbed dose in water. The dose measurement is based on
5.5 Other materials—The temperature sensors, wires, etc.
the measurement of the temperature increase in a volume of
of the calorimeter represent foreign materials, which may
water, for example, a water-filled polystyrene petri dish.
influence the total temperature rise. These components should
4.3.1 The response of the water calorimeters should be
be as small as possible.
calibrated by comparison with graphite calorimeters irradiated
5.6 Dose gradients—Dose gradients will exist within the
under precisely the same conditions.
calorimetric body when it is irradiated with 4 to 12 MeV
4.3.2 The average dose in the water calorimeter is evalu-
electrons. These gradients must be taken into account, for
ated. Dose gradients may occur in this volume and may need to
example, when other dosimeters are calibrated by intercom-
be considered when estimating dose in other materials.
parison with calorimeters.
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 increase
in a volume of polystyrene.
6.1 One Type of Graphite Calorimeter, is a disc of graphite
4.4.1 The response of the polystyrene calorimeters should
placed in a thermally-insulating material such as foamed
be calibrated by comparison with graphite calorimeters irradi-
plastic (6-8). A calibrated thermistor or thermocouple is em-
ated under precisely the same conditions.
bedded inside the disc. See Fig. 1 for an example of such a
4.4.2 The average dose in the polystyrene volume is evalu-
calorimeter. Some typical examples of graphite disc thick-
ated. Dose gradients may occur in this volume and may need to
nesses and masses are listed in Table 1 (2).
be considered when estimating dose in other materials.
6.2 A Typical Water Calorimeter, is a sealed polystyrene
4.4.3 Polymeric materials other than polystyrene may be
petri dish filled with water and placed in thermally-insulating
used for calorimetric measurements. Polystyrene is used be-
foamed plastic (6). A calibrated temperature sensor (ther-
cause it is known to be resistant to radiation (4) and because no
mistor) is placed through the side of the dish into the water. See
exo- or endothermic reactions are taking place (5).
Fig. 2 as an example of such a calorimeter.
6.3 A Typical Polystyrene Calorimeter, is a polystyrene disc
5. Interferences
placed in thermally-insulating foamed plastic. A calibrated
5.1 Extrapolation—The calorimeter designs described in
thermistor or thermocouple is imbedded inside the disc. The
this practice are usually not strictly adiabatic, because of the
dimension of the polystyrene disc may be similar to that of the
graphite and water calorimeters.
5 6.4 Radiation-resistant components should be used for the
The boldface numbers in parentheses refer to the bibliography at the end of this
parts of the calorimeter that are exposed to the electron beam.
practice.
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ISO/ASTM 51631:2002(E)
FIG. 1 Example of a Graphite Calorimeter Used at a 10–MeV
Industrial Electron Accelerator (7)
TABLE 1 Thickness and Size of Several Graphite Calorimeters
Designed at NIST for Use at Specific Electron Energies
Electron Range
Calorimeter Disc (30 mm diameter)
A
Electron
in Graphite
B
−3
Energy
Thickness
density: 1.7 g·cm
Mass,
MeV
g
−2 2
gcm cm g cm cm
4 2.32 1.36 0.84 0.49 5.9
5 2.91 1.71 1.05 0.62 7.5
6 3.48 2.05 1.25 0.74 8.9
8 4.59 2.70 1.65 0.97 11.7
10 5.66 3.33 2.04 1.20 14.4
11 6.17 3.63 2.22 1.31 15.7
12 6.68 3.93 2.40 1.41 16.9
A
This is the continuous-slowing-down approximation (CSDA) range r of elec-
o
trons for a broad beam incident on a semi-infinite absorber. It is calculated from:
E
o 1
r 5 · dE
o *
0 ~S/p!
tot
where:
E = the primary electron energy, and
o FIG. 2 Example of a Water Calorimeter Used for Routine
(S/p) = the total mass stopping power at a given electron energy (1).
tot
Measurements at a 10–MeV Industrial Electron Accelerator (6)
B
The thicknesses specified are equal to 0.36 (r ).
o
bridge or commercial calibrated thermistor readers (7).Itis
6
This also applies to insulation of electrical wires.
important for both ohm-meters and resistance bridge measure-
6.5 Good thermal contact must exist between the tempera-
ments to minimize the dissipated power in the thermistor,
ture sensor and the calorimetric body. For graphite and
preferably below 0.1 mW.
polystyrene calorimeters, this can be assured by adding a small
6.6.3 Thermocouple—Use a high-precision digital voltme-
amount of heat-conducting compound when mounting the
ter, or commercial reader (2). The sensitivity of the voltmeter
temperature sensor.
should be better than 0.1 μV.
6.6 Read-Out—The calorimeters are read by measuring the
temperature of the calorimetric body. This temperature is 7. Calibration Procedures
registered by thermistors or thermocouples.
7.1 The graphite calorimeters may be considered either as
6.6.1 Thermistor—Use a high-precision ohm-meter for
primary standard dosimetry systems or as routine dosimetry
measurement of thermistor resistance. The meter should have a
systems requiring calibration against other standards, depend-
resolution of better than 6 0.1 % and an accuracy of better than
ing on how they are used for dose measurement, while water
6 0.2 %. It should preferably be equipped for four-wire type
and polystyrene calorimeters typically are used as routine
resistance measurements, especially if the thermistor resistance
dosimeters.
is less than 10 kV. With the four-wire measurement technique,
7.2 Primary–Standard Dosimeter—In order to consider the
the effects of resistance in the measurement wires and electrical
graphite calorimeter as a primary–standard dosimeter, the
contacts are minimized.
specific heat capacity of the graphite and its temperature
6.6.2 Other appropriate instrumentation may be used for the
dependence must be known and the temperature sensors and
thermistor resistance measurement, for example, a resistance
the measuring equipment must be accurately calibrated. Any
influence of the irradiation conditions must be evaluated and
6 any possible influence on the uncertainty of the dose reading
Radiation resistant wiring is available, for example, from Huber und Suhner,
Pfäffikon, Switzerland, under the brand name Radox. must be taken into account.
© ISO/ASTM International 2002 – All rights reserved
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ISO/ASTM 51631:2002(E)
7.2.1 The specific heat capacity of the graphite of the of temperature obtained from the extrapolations are used to
calorimetric body and its functional dependence on tempera- calculate DT = T − T that would occur in the absence of heat
2 1
ture may be determined by several techniques. One method exchange with the surroundings.
employs a built-in electrical heater in the calorimetric body to 7.2.4 If the specific heat capacity is determined by other
dissipate a known amount of electrical energy (see 7.2.3 and means, then it shall be known over the expected temperature
Annex A1). Another method uses a separate adiabatic calorim- range of operation.
eter to measure specific heat of a sample of the graphite
NOTE 2—Repeated measurements of specific heat of various types of
material (8). Adiabatic calorimeters that use differential scan-
graphite have been carried out over the range of 0 to 50°C, indicating a
−1 −1
ning calorimetry techniques for specific heat measurement are
value for c of 644.2 + 2.86· T (J ·kg ·°C ), where T is the mean
G
commercially available. temperature (°C) of the graphite. This value must, however, not be
considered a universal value. (8).
7.2.2 Calibrate the temperature sensors and their associated
readout instrumentation by placing the sensors in a well- 7.3 Routine Dosimeter—Without knowledge of the specific
controlled environment with a precision, high-accuracy ther-
heat of graphite, the graphite calorimeter may be used as a
mometer whose response is traceable to national standards. If routine dosimeter. Its response shall be calibrated against
possible, place the entire calorimetric body containing the
another reference–standard dosimeter.
temperature sensors in this environment in good thermal
7.3.1 Calibration may be obtained in two ways:
contact with the calibration thermometer. An appropriate envi-
7.3.1.1 Irradiation at a calibration laboratory together with
ronment could be a stirred oil or water bath or a well-insulated
reference–standard dosimeters.
metal block. Slowly vary the temperature of the environment
7.3.1.2 Irradiation at the user’s facility together with trans-
over the range of expected use, allowing ample time for all
fer–standard dosimeters from a calibration laboratory.
components to come to thermal equilibrium. Record the 7.3.2 For irradiation in a calibration laboratory, usually the
temperature sensor readings as a function of the calibration
procedure in 8.3 may be used. Any effect on the calorimeter
thermometer readings. response in changing from the calibration laboratory to the
user’s facility must be evaluated and taken into account.
7.2.3 If the specific heat capacity of the graphite is not
7.3.3 For irradiation together with transfer dosimeters at the
known or cannot be obtained conveniently, then the calorimet-
user’s facility, the procedure given in Section 9 may be used.
ric body may be equipped with a built-in electrical heater for
7.4 Water or polystyrene calorimeters may be calibrated
calibration. This, in effect, determines the mean specific heat
against graphite calorimeters or by comparison with transfer-
capacity for a particular initial temperature and temperature
–standard dosimeters from an accredited calibration laboratory
increase.
by irradiation sequentially (or simultaneously) at an electron
7.2.3.1 The heater may consist of a resistance wire that is
accelerator. The radiation field over the cross-sectional area of
placed in the graphite calorimetric body in such a way that its
the calorimetric body shall be uniform to within 6 2 % and
heat is dissipated evenly in the graphite disc. The mass of the
constant over the time required to irradiate both calorimeters.
heater wire inside the graphite disc should be only a small
The irradiation conditions should be arranged so that the
fraction of the total mass of the two combined, preferably less
electron fluence is equal in the two calorimeters. If that is not
than 1 %.
the case, corrections or 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 function
graphite disc if a known electrical current, I, (unit: A) is
of temperature. The calibration must therefore be carried out at
allowed to flow for a known time, t, (unit: s) through the wire
a range of temperatures, so that a relationship between the
with resistance R (unit: ohm). The mean specific heat capacity,
−1
calibration factor (expressed in kGy · °C ) and the average
c , may be calculated from
G
temperature of the calorimetric body can be determined.
2
I · R · t
7.4.2 The calibration factor for water calorimeters is ap-
21 21
c 5 ~J·kg ·°C ! (1)
G
−1
DT · m
proximately 3.4 kGy · °C and for polystyrene calorimeters it
−1
is approximately 1.4 kGy · °C . For graphite, the relationship
where:
−1
is approximately 0.75 kGy ·° C (see Note 2). These values
DT = the observed temperature (unit: °C) increase from the
apply for 10 MeV irradiation of calorimeters with thickness
initial temperature, T to the maximum temperature,
o
−2
approximately 1.7g·cm .
T , and
max
7.5 Calibration of all types of calorimeters used as routine
m = 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 deter-
disc should be considered when determining the resistance R.
mined by the user.
The mean specific heat capacity determined is valid only for
8. Dose Measurement Procedures
the particular values of T and T employed. Thus, a series of
0 max
electrical calibrations are needed to cover the expected tem-
8.1 Conveyor Irradiation—For calorimeters carried on con-
perature ranges of operation.
veyors past scanned electron beams, the calorimeter is usually
7.2.3.3 To determine DT, plot the temperature versus time disconnected from the temperature measurement system just
before and after switching on the electrical current. Extrapolate prior to irradiation and reconnected for readout just after
the curves to the midpoint of the heating time. The two values
irradiation (9).
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ISO/ASTM 51631:2002(E)
D 5 c · ~T 2 T ! (2)
8.1.1 Before irradiation, measure the temperature of the
G G 2 1
calorimetric body and check that the temperature remains
where:
stable for a period of at least ten min (typically less than 0.1°C
c = the specific heat capacity of the graphite at the mean
G
change).
temperature during irradiation, (T + T )/2.
1 2
8.1.2 Disconnect the measurement wires and place the
8.1.9 The dose, D , in another material of the same dimen-
M
calorimeter on the conveyor for transport through the irradia-
sions irradiated under the same conditions is given by:
tion zone.
D 5 D · S /S (3)
8.1.3 Transport the calorimeter through the irradiation zone M G M G
on the conveyor system.
where:
8.1.4 During irradiation, record the time of irradiation, and
S and S = mass collision stopping powers of the other
M G
the irradiation parameters (electron energy, electron current,
material and graphite, respectively (see ISO/
scanned beam width, and conveyor speed).
ASTM Guide 51261 and ICRU Reports 37
8.1.5 After passage of the irradiation zone, reconnect the
and 44).
wires for measurement of temperature, and record the time
8.1.9.1 This equation is valid only when the electron flu-
from the end of irradiation to the first temperature measure-
ences in the two absorbers of interest are equal, which has been
ment. Record the temperature as a function o
...
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