1、Designation: F 526 97 (Reapproved 2003)Standard Test Method forMeasuring Dose for Use in Linear Accelerator PulsedRadiation Effects Tests1This standard is issued under the fixed designation F 526; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、 of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript 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. Scope1.1 This test
3、method covers a calorimetric measurement ofthe dose delivered in a single pulse of electrons from anelectron linear accelerator used as an ionizing source inradiation-effects testing. The test method is designed for usewith pulses of electrons in the energy range from 10 to 50 MeVand is only valid f
4、or cases in which both the calorimeter andthe test specimen to be irradiated are“ thin” compared to therange of these electrons in the materials of which they areconstructed.1.2 The procedure described can be used in those cases inwhich (1) the dose delivered in a single pulse is 5 Gy2(500rad) or gr
5、eater, or (2) multiple pulses of a lower dose can bedelivered in a time short compared to the thermal time constantof the calorimeter. The minimum dose per pulse that can beacceptably monitored depends on the variables of the particulartest, including pulse rate, pulse uniformity, and the thermaltim
6、e constant of the calorimeter.1.3 A determination of the dose is made directly for thematerial of which the calorimeter block is made. The dose inother materials can be calculated from this measured value byformulas presented in this test method. The need for suchcalculations and the choice of mater
7、ials for which calculationsare to be made shall be subject to agreement by the parties tothe test.1.4 The values stated in SI units are to be regarded as thestandard. The values in parenthesis are provided for informa-tion only.1.5 This standard does not purport to address the safetyconcerns, if any
8、, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety andhealth practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E 230 Specification and Temperature-Electromotive Force
9、(EMF) Tables for Standardized Thermocouples3. Terminology3.1 Definitions:3.1.1 thermal time constant of a calorimeterthe time forthe temperature excursion of the calorimeter resulting from aradiation pulse to drop to 1/e of its initial maximum value.4. Summary of Test Method4.1 Single-Pulse MethodTh
10、is method consists of (1) irra-diating, with a single pulse of high-energy electrons from anelectron linear accelerator (linac), a small block of material towhich either a thermistor or a thermocouple made fromsmall-diameter wire is attached; (2) recording and measuringthe resulting signal from a br
11、idge circuit or directly from thethermocouple; (3) calculating the dose deposited in the blockbased on the temperature rise and the specific heat of thematerial; and (4) if required, calculating the equivalent dose inother specified materials.4.2 Multiple-Pulse MethodIf the dose available in a singl
12、epulse is not large enough to give measurable results, the linacis pulsed repeatedly within a time short compared to thethermal time constant of the calorimeter.This method is similarto the single-pulse method except that the average dosedelivered in each pulse is calculated from the measuredcumulat
13、ive dose of all the pulses.5. Significance and Use5.1 An accurate measure of the dose during radiation-effectstesting is necessary to ensure the validity of the data taken, toenable comparison to be made of data taken at differentfacilities, and to verify that components or circuits are tested tothe
14、 radiation specification applied to the system for which theyare to be used.1This test method is under the jurisdiction of ASTM Committee F01 onElectronics and is the direct responsibility of Subcommittee F01.11 on Nuclear 1 Gy = 100 rad.3Annual Book of ASTM Standards, Vol 14.03.1Copyright ASTM Inte
15、rnational, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.2 The primary value of a calorimetric method for measur-ing dose is that the results are absolute. They are based only onphysical properties of materials, that is, the specific heat of thecalorimeter-blo
16、ck material and the Seebeck emf of the thermo-couple used or the temperature coefficient of resistance (a)ofthe thermistor used, all of which can be established withnon-radiation measurements.5.3 The method permits repeated measurements to be madeduring a radiation effects test without requiring ent
17、ry into theradiation cell between measurements.6. Interferences6.1 Thermal IsolationIf the thermal isolation of the calo-rimeter is not sufficient, the thermal time constant of thecalorimeter response will be too short for it to be useful.NOTE 1This condition can be caused by insufficient insulation
18、 mate-rial or by heat loss through the thermocouple wires themselves.6.2 Thermal EquilibriumThe initial value of the transienttemperature change following a radiation pulse may not reflectthe true temperature change of the calorimeter-block material.NOTE 2This situation can be brought about by a tem
19、perature riseoccurring in the materials at the point of attachment of the thermocoupleor the thermistor different from that in the calorimeter-block material. Aslong as the calorimeter block comprises the great bulk of the calorimetermaterial, the temperature will quickly equilibrate to that of the
20、block, andthe subsequent temperature record will be that of the calorimeter-blockmaterial (see Appendix X1).6.3 Pulse ReproducibilityIf pulse-to-pulse reproducibilityof the radiation source varies more than 620 %, a goodmeasure of the dose per pulse may not be attainable from theaverage value calcul
21、ated in the multiple-pulse method.7. Apparatus7.1 LinacElectron linear accelerator and associated in-strumentation and controls suitable for use as an ionizingsource in radiation-effects testing.7.2 CalorimeterSpecial instrument suitable for measuringthe dose delivered by the linac and constructed i
22、n accordancewith any of several designs utilizing any of several materials asindicated in Appendix X1. Although measurement differencesresulting from the use of different designs should not besignificant, all parties to the test shall agree to a single designutilizing a single calorimeter-block mate
23、rial and a specificthermocouple or thermistor. The calorimeter design shall besuch that the surface density in the beam path is less than orequal to no more than 20 % of the range of the beam-energyelectrons (see Fig. 1).7.3 D-C Low Noise Amplifier (LNA), with a gain of 1000 to10 000 (see Fig. 2).NO
24、TE 3An analog nanovoltmeter with a recorder output can also beused as a low noise amplifier. These devices produce a 1V output for afull scale reading.7.3.1 Response time no greater than 0.1 s for the amplifieroutput to reach 90 % of its final reading,FIG. 1 Block Diagram of Calorimeter Dosimeter Ci
25、rcuitF 526 97 (2003)27.3.2 Noise level less than 10 mV rms referred to the output,7.3.3 Measurement accuracy of 2 % of full scale or better,and7.3.4 Normal-mode rejection capability such that a-c volt-ages of 50 Hz and above and 60 dB greater than the rangesetting shall affect the instrument reading
26、 by less than 2 %.NOTE 4If the meter does not have an internal nulling circuit, it maybe necessary to use a simple bucking circuit to null out thermal emfs in themeasuring circuit to keep the meter on scale at the high-gain positionsused in this measurement (see Fig. 1).7.4 Data RecorderLinear-respo
27、nse recorder meeting thefollowing specifications:7.4.1 Recording speed sufficient to capture 5 to 10 s ofcalorimeter response.7.4.2 Response time for full-scale deflection of 0.1 s or less.7.4.3 Deviation of response from linearity of no more than62 %, and7.4.4 Sensitivity compatible with the record
28、er output of thed-c LNA. Typically 2mV full scale.7.5 Voltage Calibration SourceVoltage source capable ofmeeting the following specifications:7.5.1 Output voltages including 1.5, 3.0, 5.0, 10.0, 15, 30,and 50 V, and 100 V,7.5.2 Accuracy of 61 % of the selected voltage, or better,7.5.3 Thermally gene
29、rated voltages of less than 100 nV withthe source stabilized, and7.5.4 Source resistance of 100 V or less.7.6 Wheatstone Bridge Circuit, designed so that the ther-mistor forms one leg of the bridge, and so that the adjustableresistor of the bridge will be equal to the resistance of thethermistor at
30、balance (see Fig. 1B).8. Sampling8.1 The number of measurements shall be subject to agree-ment by the parties to the test.9. Calibration9.1 The LNA and data recorder should be calibrated to bewithin 6 2 % of full scale.10. Procedure10.1 Single-Pulse Method:10.1.1 Position the calorimeter at the loca
31、tion where thedose measurement is desired.10.1.2 Connect all components of the calorimetric dosim-eter system in accordance with the circuit shown in Fig. 1.FIG. 2 FIG. Recommended Low Noise Amplifier Schematic DiagramF 526 97 (2003)310.1.3 Set the LNA for a gain of 10 000 (1000), if using thethermi
32、stor circuit).10.1.4 For the thermocouple measurements, adjust eitherthe internal nulling circuit of the LNA or the external buckingcircuit so that the meter deflection caused by the quiescentlevel of the calorimeter output is less than full scale. Forthermistor measurements adjust the bridge for a
33、null. Use thezero-adjust capability of the data recorder to position therecorder trace near the center of the recorder chart.NOTE 5With either system, there will likely be a drift as thetemperature of the calorimeter equilibrates. This drift is compensated forin data reduction and may be neglected i
34、f the rate of change is much lessthan that caused by the radiation pulse.10.1.5 With the data recorder sweep speed set within therange from 0.5 to 2.0 cm/s, inclusive, trigger the recorder andpulse the linac.10.1.6 If the transient deflection of the recorder is less than10 % of full scale, set the r
35、ecorder range to the next lowerrange and repeat 10.1.5.10.1.7 Repeat 10.1.5 and 10.1.6 until a range is found forwhich the greater-than-10 % criterion is met, or until there areno more ranges to try.10.1.7.1 When a range is found for which this greater-than-10 % criterion is met, annotate the data r
36、ecorder output besidethe recorded transient with the shot number, date, LNA gain,calorimeter identification, and description of irradiation geom-etry (including scatterer thickness and distance of the calorim-eter from the scatterer) as shown in Fig. 3 and Fig. 4.10.1.7.2 If no range if found for wh
37、ich a 10 % deflection isobtained which is easily distinguishable from noise, use themultiple-pulse method beginning with 10.2.2.10.1.7.3 Otherwise, repeat 10.1.7.1 four more times.10.2 Multiple-Pulse Method:10.2.1 Carry out 10.1.1 through 10.1.4.10.2.2 With the recorder chart speed set within the ra
38、ngefrom 0.5 to 2.0 cm/s, inclusive, pulse the Linac repeatedlywithin a time that is short compared to the thermal timeconstant of the calorimeter to give a recorder deflection greaterthan 10 % of full scale.FIG. 3 Typical Chart Record of Calorimeter Dosimetry Using Single-Pulse MethodF 526 97 (2003)
39、410.2.2.1 From the data, measure the voltage rise resultingfrom this series of pulses.10.2.2.2 For the time interval beginning with the cessationof the radiation and equal in duration to the total time duringwhich the radiation dose was accumulated, measure the ther-mocouple voltage drop.10.2.2.3 Ca
40、lculate the ratio of the voltage from 10.2.2.2 tothat of 10.2.2.1.10.2.2.4 If this ratio is less than 0.15, continue with 10.2.3(the thermal time constant of the calorimeter is sufficientlygreater than the radiation time for the dose to be determinedaccurately).10.2.2.5 If this ratio is equal to or
41、greater than 0.15, repeat10.2.2 through 10.2.2.5 using a higher pulse repetition rate fora shorter radiation time period.10.2.3 Annotate the data recorder output, as well as thenumber of pulses used (see Fig. 5, Fig. 6, and Fig. 7).10.2.4 Repeat 10.2.2 and 10.2.3 four more times, omittingthe time co
42、nstant determination (10.2.2.1 through 10.2.2.5).11. Calculation and Interpretation of Results11.1 Single-Pulse Method:11.1.1 On the recorder output, determine the perpendicularto the time axis at the start of each transient, as shown in Fig.3.11.1.2 Determine whether a period of time was required f
43、orthe temperature to equilibrate after the pulse, as indicated bythe presence of a spike (Fig. 5a) or a flat portion (Fig. 5b) of thedata recorder trace at the end of the transient.11.1.2.1 If no such feature is present, draw a line extrapo-lating the steepest part of the cooling curve following eac
44、hradiation pulse back to intersect the perpendicular line (see11.1.1). When using digital storage ocilloscopes, built incursors usually can be used.NOTE 6These lines are dashed in Fig. 3.11.1.2.2 If such a feature is present, draw a line extrapolat-ing from the slope of the curve where a smooth cool
45、ing trendresumes. Do this for each pulse.NOTE 7These lines are dashed in Fig. 5.11.1.3 Measure along each perpendicular line the lengthfrom the start of each transient to the intersection of theperpendicular line with the extrapolated line.11.1.4 Convert these measurements to output voltage level.11
46、.1.5 For each pulse calculate and record the dose in Gy(calorimeter-block material) producing the transient, using fora thermocouple measurement, the relation:Dose 5 100 Vcp/ PG (1)FIG. 4 Typical Digital Oscilloscope Recording of the Calorimeter ResponseTABLE 1 Physical Properties of Some Calorimete
47、r-BlockMaterialsMaterialEnergy LossAdE/dx(1014Jm2/kg)Specific Heat, cpB(J/kgK)Density, rB(103kg/m3)C 2.92 711 2.10Al 2.74 900 2.70Si 2.84 711 2.33Fe 2.52 452 7.87Cu 2.42 385 8.96Ge 2.45 322 5.32W 2.08 134 19.3Au 2.06 130 19.3Pb 2.07 128 11.4AThe data are given for 20-MeV electrons, but ratios based
48、on these values aregood to better than 2 % over the energy range from 10 to 50 MeV, inclusive. Thesevalues have been converted to SI units from data given in the tables of Berger andSeltzer: Tables of Energy Losses and Ranges of Electrons and Positrons, NASASP-3012 (1964); and Additional Stopping Po
49、wers and Range Tables for Protons,Mesons, and Electrons, NASA SP-3036 (1966).BThese values have been converted to SI units from data given in the Handbookof Tables for Applied Engineering Science, 2nd ed., CRC Press, Cleveland, OH(1973). (The specific heat values are applicable in the range from 18 to 30C,inclusive.)F 526 97 (2003)5where:V = deflection caused by irradiation pulse, in microme-tres,cp= specific heat of calorimeter-block material, J/kgK,P = temperature coefficient of the calorimeter thermo-couple in the vicinity of room temperature, V/K,G = g
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