1、Designation: F526 16Standard 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 U.S. Department of Defense.1. Scope1.1 This t
3、est method covers a calorimetric measurement ofthe total absorbed dose delivered in a single pulse of electronsfrom an electron linear accelerator or a flash X-ray machine(FXR, e-beam mode) used as an ionizing source in radiation-effects testing. The test method is designed for use with pulsesof ele
4、ctrons in the energy 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
5、 (1) the dose delivered in a single pulse is 5 Gy(matl)2500 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. The units for the total absorbeddose delivered to a material require the specification of
6、thematerial and the notation “matl” refers to the active material ofthe calorimeter. The minimum dose per pulse that can beacceptably monitored depends on the variables of the particulartest, including pulse rate, pulse uniformity, and the thermaltime constant of the calorimeter.1.3 Adetermination o
7、f the total dose is made directly for thematerial of which the calorimeter block is made. The total dosein other materials can be calculated from this measured valueby formulas presented in this test method. The need for suchcalculations and the choice of materials for which calculationsare to be ma
8、de 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, associated with its use. It is the re
9、sponsibilityof 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:3E170 Terminology Relating to Radiation Measurements andDosimetryE230 Specification and Tempera
10、ture-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 (DUT)the device that is under thecurrent test.3.1.2 Seebeck EMFthe electromagnetic force (EMF)
11、gen-erated by the Seebeck effect when two wires composed ofdissimilar metals are joined at both ends and the ends are heldat different temperatures.Avoltage can be measured across theterminals when current flows through the wires.3.1.3 temperature coeffcient of resistancethe resistancechange in a ma
12、terial per degree of temperature change d/(*d), where denotes the resistance and denotes thetemperature. This quantity has units of inverse temperatureand, for small changes about a reference temperature in aconductor, this quantity is often modeled as a linear relation-ship with temperature.3.1.4 t
13、hermal 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.3.1.5 TSPtwisted shielded pair, a shielded case of atwisted pair cable in which two conductors are twisted together1This test meth
14、od is under the jurisdiction ofASTM Committee E10 on NuclearTechnology and Applications and is the direct responsibility of SubcommitteeE10.07 on Radiation Dosimetry for Radiation Effects on Materials and Devices.Current edition approved June 1, 2016. Published July 2016. Originallypublished as F526
15、 77 T. Last previous edition approved in 2011 as F526 11.DOI: 10.1520/F0526-16.2In 1975 the General Conference onWeights and Measures adopted the unit gray(symbolGy) for absorbed dose; 1 Gy = 100 rad.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Servic
16、e at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1for the purpose of canceling out electromagneti
17、c interferencefrom external sources.3.2 Definitions of other terms used in this standard thatpertain to radiation measurements and dosimetry may be foundin Terminology E170.4. Summary of Test Method4.1 Single-Pulse MethodThis method consists of (1)irradiating, with a single pulse of high-energy elec
18、trons froman electron 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 bridgecircuit or directly from the thermocouple; (3)
19、 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 materialsexposed to this same pulse.4.2 Multiple-Pulse MethodIf the dose available in a singlepulse is not larg
20、e 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 measuredcumulative dose of all t
21、he pulses.5. Significance and Use5.1 An accurate measure of the total absorbed dose isnecessary to ensure the validity of the data taken, to enablecomparison to be made of data taken at different facilities, andto verify that components or circuits are tested to the radiationspecification applied to
22、 the system for which they are to beused.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-block material and the Seebeck EMF of the ther-mocouple u
23、sed or the temperature coefficient of resistance ()of the thermistor 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 Isolation
24、If 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 insulationmaterial or by heat loss through the thermocouple wires themselves.6.2 Thermal Equil
25、ibriumThe 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 temperature riseoccurring in the materials at the point of attachment of the thermocouple
26、or 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 block, andthe subsequent temperature record will be that of the calorimeter-blockmater
27、ial (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 calculated in the multiple-pulse method.6.4 Facility Spot SizeIf the calorimeter is used in
28、high-dose rate positions, the spot size (especially in ebeam facilities)may not be large enough to adequately cover the calorimetermaterial.7. Apparatus7.1 Pulsed Electron Source:7.1.1 LinacElectron linear accelerator and associated in-strumentation and controls suitable for use as an ionizingsource
29、 in radiation-effects testing. See Guide E1894.7.1.2 FXRFlash X-ray system that provides intensebremsstrahlung radiation environments, usually in a singlesub-microsecond pulse, and which can often fluctuate inamplitude, shape, and spectrum from shot to shot. This systemcan be operated in an electron
30、 beam mode by not utilizing thebremsstrahlung converter. See Guide E1894.7.2 CalorimeterSpecial instrument suitable for measuringthe total dose delivered by the linac and constructed inaccordance with any of several designs utilizing any of severalmaterials as indicated in Appendix X1.Although measu
31、rementdifferences resulting from the use of different designs shouldnot be significant, all parties to the test shall agree to a singledesign utilizing a single calorimeter-block material and aspecific thermocouple or thermistor. The calorimeter designshall be such that the surface density in the be
32、am path is lessthan or equal to no more than 20 % of the range of thebeam-energy electrons (see Fig. 1).7.3 D-C Low Noise 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
33、1V output for afull scale reading.7.3.1 Response time less than 0.1 s for the amplifier outputto reach 90 % of its final 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
34、volt-ages of 50 Hz and above and 60 dB greater than the rangesetting shall affect the instrument reading 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 inthe measuring circuit to keep the mete
35、r on scale at the high-gain positionsused in this measurement (see Fig. 1).7.4 Data RecorderLinear-response recorder or digital os-cilloscope meeting the following specifications:7.4.1 Recording duration sufficient to capture 5 to 10 s ofcalorimeter response.7.5 Voltage Calibration SourceVoltage sou
36、rce capable ofmeeting the following specifications:F526 1627.5.1 Output voltages including 1.5, 3.0, 5.0, 10.0, 15, 30,50, and 100 V,7.5.2 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
37、of 100 or less.7.6 Wheatstone Bridge Circuit, designed so that the therm-istor forms one leg of the bridge, and so that the adjustableresistor 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 m
38、ode generally provides a higher dose ratethan similar machines operated in photon, for example,bremsstrahlung, mode. However, testing in the e-beam moderequires that appropriate precautions be taken and special testfixtures be used to ensure meaningful results. The beamproduces a large magnetic fiel
39、d, which may interfere with theinstrumentation, and can induce large circulating currents indevice leads and metals.The beam also produces air ionization,induced charge on open leads, and unwanted cable currents andvoltages. E-beam testing is generally performed with thedevice-under-test (DUT) mount
40、ed in a vacuum to reduce airionization effects. Some necessary precautions are:7.7.1 The electron beam must be constrained to the regionthat 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 th
41、e FXR to prevent unwanted currentsin cables and secondary radiation in the exposure room.7.7.3 All cables and wires must be protected 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 cabl
42、e.7.7.4 An evacuated chamber for the test is required toreduce the effects of air ionization.8. Sampling8.1 The number of measurements shall be subject to agree-ment by the parties to the test.9. Calibration9.1 The LNAand recorder should be calibrated to be within62 % of full scale.10. Procedure10.1
43、 Single-Pulse Method:10.1.1 Position the calorimeter at the location 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. 1.10.1.3 Set the LNA for a gain of 10 000 (or 1000, if usingthe thermistor circui
44、t).FIG. 1 Typical Block Diagram of Calorimeter Dosimeter CircuitF526 163NOTE 5A LNA is not always needed if the calorimeter is used at highdose positions. The signal for some calorimeter materials can be quitelarge.10.1.4 For the thermocouple measurements, adjust eitherthe internal nulling circuit o
45、f 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-adjust capability of the data recorder to position therecorder trace near the cen
46、ter of the recorder chart. If using anoscilloscope, adjust the settings accordingly to make sure thatthe response if noticeable within the oscilloscope window.Refer to the oscilloscope manual to ensure that the properresolution are set to capture the response signal.NOTE 6With either system, there w
47、ill 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 If using a data recorder sweep speed set within therange from 0.5 to 2.0 cm/s,
48、 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 taken if multiple pulses are going to beadministered, because of the temperatur
49、e that the pulses generate, whichwill cause the calorimeter to rise. The protocol for establishing thetemperature in a multiple irradiation shall be established before the testingis initiated, for example, it should be stated up front if you are going to usethe average from a specified number of pulses as being representative ofall shots. This protocol should be done two or three times during a shotday. If you want best accuracy, wait for the calorimeter to cool downbetween pulses and allow the calorimeter signal to use at least half thera
