ASTM F526-97

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: F 526 – 97
Standard Test Method for
Measuring Dose for Use in Linear Accelerator Pulsed
Radiation Effects Tests
This standard is issued under the fixed designation F 526; 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 (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 2. Referenced Documents
1.1 This test method covers a calorimetric measurement of 2.1 ASTM Standards:
the dose delivered in a single pulse of electrons from an E 230 Temperature Electromotive Force (EMF) Tables for
electron linear accelerator used as an ionizing source in Standardized Thermocouples
radiation-effects testing. The test method is designed for use
3. Terminology
with pulses of electrons in the energy range from 10 to 50 MeV
and is only valid for cases in which both the calorimeter and 3.1 Definitions:
3.1.1 thermal time constant of a calorimeter—the time for
the test specimen to be irradiated are“ thin” compared to the
range of these electrons in the materials of which they are the temperature excursion of the calorimeter resulting from a
radiation pulse to drop to 1/e of its initial maximum value.
constructed.
1.2 The procedure described can be used in those cases in
2 4. Summary of Test Method
which (1) the dose delivered in a single pulse is 5 Gy (500
4.1 Single-Pulse Method—This method consists of (1) irra-
rad) or greater, or (2) multiple pulses of a lower dose can be
diating, with a single pulse of high-energy electrons from an
delivered in a time short compared to the thermal time constant
electron linear accelerator (linac), a small block of material to
of the calorimeter. The minimum dose per pulse that can be
which either a thermistor or a thermocouple made from
acceptably monitored depends on the variables of the particular
small-diameter wire is attached; (2) recording and measuring
test, including pulse rate, pulse uniformity, and the thermal
the resulting signal from a bridge circuit or directly from the
time constant of the calorimeter.
thermocouple; (3) calculating the dose deposited in the block
1.3 A determination of the dose is made directly for the
based on the temperature rise and the specific heat of the
material of which the calorimeter block is made. The dose in
material; and (4) if required, calculating the equivalent dose in
other materials can be calculated from this measured value by
other specified materials.
formulas presented in this test method. The need for such
4.2 Multiple-Pulse Method—If the dose available in a single
calculations and the choice of materials for which calculations
pulse is not large enough to give measurable results, the linac
are to be made shall be subject to agreement by the parties to
is pulsed repeatedly within a time short compared to the
the test.
thermal time constant of the calorimeter. This method is similar
1.4 The values stated in SI units are to be regarded as the
to the single-pulse method except that the average dose
standard. The values in parenthesis are provided for informa-
delivered in each pulse is calculated from the measured
tion only.
cumulative dose of all the pulses.
1.5 This standard does not purport to address the safety
concerns, if any, associated with its use. It is the responsibility
5. Significance and Use
of the user of this standard to establish appropriate safety and
5.1 An accurate measure of the dose during radiation-effects
health practices and determine the applicability of regulatory
testing is necessary to ensure the validity of the data taken, to
limitations prior to use.
enable comparison to be made of data taken at different
facilities, and to verify that components or circuits are tested to
This test method is under the jurisdiction of ASTM Committee F-1 on
the radiation specification applied to the system for which they
Electronics, and is the direct responsibility of Subcommittee F01.11 on Quality and
are to be used.
Hardness Assurance.
Current edition approved Dec. 10, 1997. Published March 1998. Originally
published as F 526 – 77 T. Last previous edition F 526 – 91.
In 1975 the General Conference on Weights and Measures adopted the unit gray
(symbol—Gy) for absorbed dose; 1 Gy = 100 rad. Annual Book of ASTM Standards, Vol 14.03.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 526–97
5.2 The primary value of a calorimetric method for measur- 6.3 Pulse Reproducibility—If pulse-to-pulse reproducibility
ing dose is that the results are absolute. They are based only on of the radiation source varies more than 620 %, a good
physical properties of materials, that is, the specific heat of the measure of the dose per pulse may not be attainable from the
calorimeter-block material and the Seebeck emf of the thermo- average value calculated in the multiple-pulse method.
couple used or the temperature coefficient of resistance (a)of
7. Apparatus
the thermistor used, all of which can be established with
non-radiation measurements. 7.1 Linac—Electron linear accelerator and associated in-
5.3 The method permits repeated measurements to be made strumentation and controls suitable for use as an ionizing
source in radiation-effects testing.
during a radiation effects test without requiring entry into the
radiation cell between measurements. 7.2 Calorimeter—Special instrument suitable for measuring
the dose delivered by the linac and constructed in accordance
6. Interferences
with any of several designs utilizing any of several materials as
indicated in Appendix X1. Although measurement differences
6.1 Thermal Isolation—If the thermal isolation of the calo-
resulting from the use of different designs should not be
rimeter is not sufficient, the thermal time constant of the
significant, all parties to the test shall agree to a single design
calorimeter response will be too short for it to be useful.
utilizing a single calorimeter-block material and a specific
NOTE 1—This condition can be caused by insufficient insulation mate-
thermocouple or thermistor. The calorimeter design shall be
rial or by heat loss through the thermocouple wires themselves.
such that the surface density in the beam path is less than or
6.2 Thermal Equilibrium—The initial value of the transient
equal to no more than 20 % of the range of the beam-energy
temperature change following a radiation pulse may not reflect
electrons (see Fig. 1).
the true temperature change of the calorimeter-block material.
7.3 D-C Low Noise Amplifier (LNA), with a gain of 1000 to
10 000 (see Fig. 2).
NOTE 2—This situation can be brought about by a temperature rise
occurring in the materials at the point of attachment of the thermocouple
NOTE 3—An analog nanovoltmeter with a recorder output can also be
or the thermistor different from that in the calorimeter-block material. As
used as a low noise amplifier. These devices produce a 1–V output for a
long as the calorimeter block comprises the great bulk of the calorimeter
full scale reading.
material, the temperature will quickly equilibrate to that of the block, and
7.3.1 Response time no greater than 0.1 s for the amplifier
the subsequent temperature record will be that of the calorimeter-block
material (see Appendix X1). output to reach 90 % of its final reading,
FIG. 1 Block Diagram of Calorimeter Dosimeter Circuit
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F 526–97
FIG. 2 FIG. Recommended Low Noise Amplifier Schematic Diagram
7.3.2 Noise level less than 10 mV rms referred to the output, 7.5.2 Accuracy of 61 % of the selected voltage, or better,
7.3.3 Measurement accuracy of 2 % of full scale or better, 7.5.3 Thermally generated voltages of less than 100 nV with
and the source stabilized, and
7.3.4 Normal-mode rejection capability such that a-c volt- 7.5.4 Source resistance of 100 V or less.
ages of 50 Hz and above and 60 dB greater than the range 7.6 Wheatstone Bridge Circuit, designed so that the ther-
setting shall affect the instrument reading by less than 2 %. mistor forms one leg of the bridge, and so that the adjustable
resistor of the bridge will be equal to the resistance of the
NOTE 4—If the meter does not have an internal nulling circuit, it may
thermistor at balance (see Fig. 1B).
be necessary to use a simple bucking circuit to null out thermal emfs in the
measuring circuit to keep the meter on scale at the high-gain positions
8. Sampling
used in this measurement (see Fig. 1).
8.1 The number of measurements shall be subject to agree-
7.4 Data Recorder—Linear-response recorder meeting the
ment by the parties to the test.
following specifications:
7.4.1 Recording speed sufficient to capture 5 to 10 s of
9. Calibration
calorimeter response.
9.1 The LNA and data recorder should be calibrated to be
7.4.2 Response time for full-scale deflection of 0.1 s or less.
within 6 2 % of full scale.
7.4.3 Deviation of response from linearity of no more than
62 %, and
10. Procedure
7.4.4 Sensitivity compatible with the recorder output of the
d-c LNA. Typically 2mV full scale. 10.1 Single-Pulse Method:
7.5 Voltage Calibration Source—Voltage source capable of 10.1.1 Position the calorimeter at the location where the
meeting the following specifications: dose measurement is desired.
7.5.1 Output voltages including 1.5, 3.0, 5.0, 10.0, 15, 30, 10.1.2 Connect all components of the calorimetric dosim-
and 50 μV, and 100 μV, eter system in accordance with the circuit shown in Fig. 1.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
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F 526–97
10.1.3 Set the LNA for a gain of 10 000 (1000), if using the 10.1.7 Repeat 10.1.5 and 10.1.6 until a range is found for
which the greater-than-10 % criterion is met, or until there are
thermistor circuit).
no more ranges to try.
10.1.4 For the thermocouple measurements, adjust either
10.1.7.1 When a range is found for which this greater-than-
the internal nulling circuit of the LNA or the external bucking
10 % criterion is met, annotate the data recorder output beside
circuit so that the meter deflection caused by the quiescent
the recorded transient with the shot number, date, LNA gain,
level of the calorimeter output is less than full scale. For
calorimeter identification, and description of irradiation geom-
thermistor measurements adjust the bridge for a null. Use the
etry (including scatterer thickness and distance of the calorim-
zero-adjust capability of the data recorder to position the
eter from the scatterer) as shown in Fig. 3 and Fig. 4.
recorder trace near the center of the recorder chart.
10.1.7.2 If no range if found for which a 10 % deflection is
NOTE 5—With either system, there will likely be a drift as the
obtained which is easily distinguishable from noise, use the
temperature of the calorimeter equilibrates. This drift is compensated for
multiple-pulse method beginning with 10.2.2.
in data reduction and may be neglected if the rate of change is much less
10.1.7.3 Otherwise, repeat 10.1.7.1 four more times.
than that caused by the radiation pulse.
10.2 Multiple-Pulse Method:
10.1.5 With the data recorder sweep speed set within the
10.2.1 Carry out 10.1.1 through 10.1.4.
range from 0.5 to 2.0 cm/s, inclusive, trigger the recorder and
10.2.2 With the recorder chart speed set within the range
pulse the linac.
from 0.5 to 2.0 cm/s, inclusive, pulse the Linac repeatedly
10.1.6 If the transient deflection of the recorder is less than within a time that is short compared to the thermal time
10 % of full scale, set the recorder range to the next lower constant of the calorimeter to give a recorder deflection greater
range and repeat 10.1.5. than 10 % of full scale.
FIG. 3 Typical Chart Record of Calorimeter Dosimetry Using Single-Pulse Method
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F 526–97
FIG. 4 Typical Digital Oscilloscope Recording of the Calorimeter Response
10.2.2.1 From the data, measure the voltage rise resulting 11.1.2.2 If such a feature is present, draw a line extrapolat-
from this series of pulses.
10.2.2.2 For the time interval beginning with the cessation
of the radiation and equal in duration to the total time during
TABLE 1 Physical Properties of Some Calorimeter-Block
Materials
which the radiation dose was accumulated, measure the ther-
A B B 3
mocouple voltage drop. Energy Loss dE/dx Specific Heat, c Density, r (10
p
Material
−14 2 3
(10 J·m /kg) (J/kg·K) kg/m )
10.2.2.3 Calculate the ratio of the voltage from 10.2.2.2 to
C 2.92 711 2.10
that of 10.2.2.1.
Al 2.74 900 2.70
10.2.2.4 If this ratio is less than 0.15, continue with 10.2.3
Si 2.84 711 2.33
Fe 2.52 452 7.87
(the thermal time constant of the calorimeter is sufficiently
Cu 2.42 385 8.96
greater than the radiation time for the dose to be determined
Ge 2.45 322 5.32
accurately).
W 2.08 134 19.3
Au 2.06 130 19.3
10.2.2.5 If this ratio is equal to or greater than 0.15, repeat
Pb 2.07 128 11.4
10.2.2 through 10.2.2.5 using a higher pulse repetition rate for
A
The data are given for 20-MeV electrons, but ratios based on these values are
a shorter radiation time period.
good to better than 2 % over the energy range from 10 to 50 MeV, inclusive. These
10.2.3 Annotate the data recorder output, as well as the
values have been converted to SI units from data given in the tables of Berger and
Seltzer: Tables of Energy Losses and Ranges of Electrons and Positrons, NASA
number of pulses used (see Fig. 5, Fig. 6, and Fig. 7).
SP-3012 (1964); and Additional Stopping Powers and Range Tables for Protons,
10.2.4 Repeat 10.2.2 and 10.2.3 four more times, omitting
Mesons, and Electrons, NASA SP-3036 (1966).
B
the time constant determination (10.2.2.1 through 10.2.2.5).
These values have been converted to SI units from data given in the Handbook
of Tables for Applied Engineering Science, 2nd ed., CRC Press, Cleveland, OH
(1973). (The specific heat values are applicable in th
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