1、Designation: F526 11Standard Test Method forUsing Calorimeters for Total Dose Measurements in PulsedLinear Accelerator or Flash X-ray Machines1This standard is issued under the fixed designation F526; the number immediately following the designation indicates the year of originaladoption or, in the
2、case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon () 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 m
3、ethod covers a calorimetric measurement ofthe total dose delivered in a single pulse of electrons from anelectron linear accelerator or a flash X-ray machine (FXR,e-beam mode) used as an ionizing source in radiation-effectstesting. The test method is designed for use with pulses ofelectrons in the e
4、nergy range from 10 to 50 MeV and is onlyvalid for cases in which both the calorimeter and the testspecimen to be irradiated are“thin” compared to the range ofthese electrons in the materials of which they are constructed.1.2 The procedure described can be used in those cases inwhich (1) the dose de
5、livered in a single pulse is 5 Gy (matl)2(500 rd (matl) or greater, or (2) multiple pulses of a lower dosecan be delivered in a short time compared to the thermal timeconstant of the calorimeter. Matl refers to the material of thecalorimeter. The minimum dose per pulse that can be accept-ably monito
6、red depends on the variables of the particular test,including pulse rate, pulse uniformity, and the thermal timeconstant of the calorimeter.1.3 Adetermination of the total dose is made directly for thematerial of which the calorimeter block is made. The total dosein other materials can be calculated
7、 from this measured valueby formulas presented in this test method. The need for suchcalculations and the choice of materials 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 i
8、n parenthesis are provided for informa-tion only.1.5 This standard does not purport to address the safetyconcerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety andhealth practices and determine the applicability of regulatoryli
9、mitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E230 Specification and Temperature-Electromotive Force(EMF) Tables for Standardized ThermocouplesE1894 Guide for Selecting Dosimetry Systems for Applica-tion in Pulsed X-Ray Sources3. Terminology3.1 Definitions:3.1.1 device under test
10、 (DUT)the device that is under thecurrent test.3.1.2 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 MethodThis method consists of (1)
11、irra-diating, with a single pulse of high-energy electrons from anelectron linear accelerator (linac) or flash X-ray machine(FXR), a small block of material to which either a thermistor ora thermocouple made from small-diameter wire is attached; (2)recording and measuring the resulting signal from a
12、 bridgecircuit or directly from the thermocouple; (3) calculating thetotal dose deposited in the block based on the temperature riseand the specific heat of the material; and (4) if required,calculating the equivalent dose in other specified materials.4.2 Multiple-Pulse MethodIf the dose available i
13、n a singlepulse 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 measur
14、edcumulative dose of all the pulses.5. Significance and Use5.1 An accurate measure of the dose is necessary to ensurethe validity of the data taken, to enable comparison to be made1This test method is under the jurisdiction of ASTM Committee F01 onElectronics and is the direct responsibility of Subc
15、ommittee F01.11 on Nuclear andSpace Radiation Effects.Current edition approved Jan. 1, 2011. Published February 2011. Originallypublished as F526 77 T. Last previous edition approved in 2003 asF526 97(2003). DOI: 10.1520/F0526-11.2In 1975 the General Conference onWeights and Measures adopted the uni
16、t gray(symbolGy) for absorbed dose; 1 Gy = 100 rad.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright
17、 ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.of data taken at different facilities, and to verify that compo-nents or circuits are tested to the radiation specification appliedto the system for which they are to be used.5.2 The primary valu
18、e 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-block material and the Seebeck EMF of the ther-mocouple used or the temperature coefficient of resistance (a)of the th
19、ermistor used, all of which can be established withnon-radiation measurements.5.3 The method permits repeated measurements to be madewithout requiring entry into the radiation cell between mea-surements.6. Interferences6.1 Thermal IsolationIf the thermal isolation of the calo-rimeter is not sufficie
20、nt, 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 mate-rial or by heat loss through the thermocouple wires themselves.6.2 Thermal EquilibriumThe initial value of the transienttemperature change
21、 following a radiation pulse may not reflectthe true temperature change of the calorimeter-block material.NOTE 2This situation can be brought about by a temperature riseoccurring in the materials at the point of attachment of the thermocoupleor the thermistor different from that in the calorimeter-b
22、lock material. Aslong as the calorimeter block comprises the great bulk of the calorimetermaterial, the temperature will quickly equilibrate to that of the block, andthe subsequent temperature record will be that of the calorimeter-blockmaterial (see Appendix X1).6.3 Pulse ReproducibilityIf pulse-to
23、-pulse reproducibilityof the radiation source varies more than 620 %, a goodmeasure of the dose per pulse may not be attainable from theaverage value calculated in the multiple-pulse method.6.4 Facility Spot SizeIf the calorimeter is used in high-dose rate positions, the spot size (especially in ebe
24、am facilities)may not be large enough to adequately cover the calorimetermaterial.7. Apparatus7.1 LinacElectron linear accelerator and associated in-strumentation and controls suitable for use as an ionizingsource in radiation-effects testing. See Guide E1894.7.2 CalorimeterSpecial instrument suitab
25、le for measuringthe dose delivered by the linac and constructed in 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
26、agree to a single designutilizing a single calorimeter-block material 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 No
27、ise Amplifier (LNA), with a gain of 1000 to10 000 (see Fig. 2).NOTE 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 less than 0.1 s for the amplifier outputto reach 90 % of its fin
28、al reading,7.3.2 Noise level less than 10 mV rms referred to the output,7.3.3 Measurement accuracy of 2 % of full scale or better,7.3.4 Normal-mode rejection capability such that AC volt-ages of 50 Hz and above and 60 dB greater than the rangesetting shall affect the instrument reading by less than
29、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 inthe measuring circuit to keep the meter on scale at the high-gain positionsused in this measurement (see Fig. 1).7.4 Data RecorderLinear-response recorder o
30、r oscillo-scope meeting the following specifications:7.4.1 Recording duration sufficient to capture 5 to 10 s ofcalorimeter response.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, 30,50, and 100 V,7
31、.5.2 Accuracy of 61 % of the selected voltage, or better,7.5.3 Thermally generated 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 adjustab
32、leresistor of the bridge will be equal to the resistance of thethermistor at balance (see Fig. 1B).7.7 Flash X-ray Machine (E-beam Mode)An FXR oper-ated in the e-beam mode generally provides a higher dose ratethan similar machines operated in photon, for example,bremsstrahlung, mode. However, testin
33、g in the e-beam moderequires that appropriate precautions be taken and special testfixtures be used to ensure meaningful results. The beamproduces a large magnetic field, which may interfere with theinstrumentation, and can induce large circulating currents indevice leads and metals.The beam also pr
34、oduces air ionization,induced charge on open leads, and unwanted cable currents andvoltages. E-beam testing is generally performed with thedevice-under-test (DUT) mounted in a vacuum to reduce airionization effects. Some necessary precautions are:7.7.1 The electron beam must be constrained to the re
35、gionthat is to be irradiated. Support circuits and components mustbe properly shielded.7.7.2 The electron beam must be stopped within the testchamber and returned to the FXR to prevent unwanted currentsin cables and secondary radiation in the exposure room.7.7.3 All cables and wires must be protecte
36、d from exposureto prevent extraneous currents. These currents may be causedby direct deposition of the beam in cables, or by magneticcoupling of the beams into the cable.7.7.4 An evacuated chamber for the test is required toreduce the effects of air ionization.8. Sampling8.1 The number of measuremen
37、ts shall be subject to agree-ment by the parties to the test.F526 1129. Calibration9.1 The LNAand recorder should be calibrated to be within62 % of full scale.10. Procedure10.1 Single-Pulse Method:10.1.1 Position the calorimeter at the location where thedose measurement is desired.10.1.2 Connect all
38、 components of the calorimetric dosim-eter system in accordance with the circuit shown in Fig. 1.10.1.3 Set the LNA for a gain of 10 000 (or 1000, if usingthe thermistor circuit).NOTE 5ALNAis not always needed if the calorimeter is used at highdose positions. The signal is often quite large.10.1.4 F
39、or 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 null. Use thezero-adju
40、st capability of the data recorder to position therecorder trace near the center of the recorder chart. If using theoscilloscope, adjust the settings accordingly to make sure thatthe response if noticeable within the oscilloscope window.Refer to the oscilloscope manual to ensure that the properresol
41、ution are set to capture the response signal.NOTE 6With 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 if the rate of change is much lessthan that caused by the radiation pulse.10.1.5
42、If using a data recorder sweep speed set within therange from 0.5 to 2.0 cm/s, inclusive, trigger the recorder andpulse the source.10.1.6 If the transient deflection of the recorder is less than10 % of full scale, set the recorder range to the next lowerrange and repeat 10.1.5.NOTE 7Care should be t
43、aken if multiple pulses are going to beadministered, because of the temperature that the pulses emit, which willcause the calorimeter to rise. It should be stated up front that you are goingto use a five pulse average as being representative of all shots. This testshould be done two or three times d
44、uring a shot day. If you want bestaccuracy, wait for the calorimeter to cool down between pulses and allowthe calorimeter signal to use at least half the range.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
45、try.10.1.7.1 When a range is found for which this greater-than-10 % criterion is met, annotate the data recorder output besidethe recorded transient with the shot number, date, LNA gain,calorimeter identification, and description of irradiation geom-etry (including scatterer thickness and distance o
46、f the calorim-eter from the scatterer) as shown in Fig. 3 and Fig. 4.FIG. 1 Typical Block Diagram of Calorimeter Dosimeter CircuitF526 11310.1.7.2 If no range if found for which a 10 % deflection isobtained which is easily distinguishable from noise, use themultiple-pulse method beginning with 10.2.
47、2.10.1.7.3 Otherwise, repeat 10.1.7.1 four more times.10.1.7.4 If using an oscilloscope, set the necessary param-eters to capture the response. Refer to the oscilloscpoe refer-ence manual to set the parameters.10.2 Multiple-Pulse Method:10.2.1 Carry out 10.1.1 through 10.1.4.10.2.2 If using the reco
48、rder chart speed set within the rangefrom 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.10.2.2.1 From the data, measure the voltage rise resultingf
49、rom 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 Calculate 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 greater than 0.15, re
