1、Designation: E1894 13Standard Guide forSelecting Dosimetry Systems for Application in PulsedX-Ray Sources1This standard is issued under the fixed designation E1894; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r
2、evision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide provides assistance in selecting and usingdosimetry systems in flash X-ray experiments. Both dose anddose-rate te
3、chniques are described.1.2 Operating characteristics of flash X-ray sources aregiven, with emphasis on the spectrum of the photon output.1.3 Assistance is provided to relate the measured dose to theresponse of a device under test (DUT). The device is assumedto be a semiconductor electronic part or s
4、ystem.2. Referenced Documents2.1 ASTM Standards:2E170 Terminology Relating to Radiation Measurements andDosimetryE666 Practice for Calculating Absorbed Dose From Gammaor X RadiationE668 Practice for Application of Thermoluminescence-Dosimetry (TLD) Systems for Determining AbsorbedDose in Radiation-H
5、ardness Testing of Electronic DevicesE1249 Practice for Minimizing Dosimetry Errors in Radia-tion Hardness Testing of Silicon Electronic Devices UsingCo-60 SourcesISO/ASTM 51261 Guide for Selection and Calibration ofDosimetry Systems for Radiation ProcessingISO/ASTM 51275 Practice for Use of a Radio
6、chromic FilmDosimetry systemISO/ASTM 51310 Practice for Use of a RadiochromicOptical Waveguide Dosimetry system2.2 International Commission on Radiation Units (ICRU)and Measurements Reports:3ICRU Report 14 Radiation Dosimetry: X rays and GammaRays with Maximum Photon Energies Between 0.6 and 50MeVIC
7、RU Report 17 Radiation Dosimetry: X rays Generated atPotentials of 5 to 150 kVICRU Report 33 Radiation Quantities and UnitsICRU Report 34 The Dosimetry of Pulsed Radiation3. Terminology3.1 absorbed dosequotient of de/dm, where de is the meanenergy imparted by ionizing radiation to matter of mass dm:
8、D 5ddme (1)See ICRU Report 33. The special name for the unit forabsorbed dose is the gray (Gy).1Gy5 1J/kg (2)Formerly, the special unit for absorbed dose was the rad,where 1 rad = 100 erg/g.1 rad 5 0.01 Gy (3)Since the absorbed dose due to a given radiation field ismaterial dependent, it is importan
9、t to include the materialcomposition for which the dose is being reported, e.g., 15.3Gy(LiF).3.2 absorbed dose enhancementincrease (or decrease) inthe absorbed dose (as compared to the equilibrium absorbeddose) at a point in a material of interest. This can be expectedto occur near an interface with
10、 a material of higher or loweratomic number.3.3 convertera target for electron beams, generally of ahigh atomic number material, in which bremsstrahlung X-raysare produced by radiative energy losses of the incident elec-trons.1This practice is under the jurisdiction of ASTM Committee E10 on NuclearT
11、echnology 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, 2013. Published July 2013. Originally approvedin 1997. Last previous edition approved in 2008 as E1894 08. DOI: 10.
12、1520/E1894-13.2For 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.3Available from the International Commission on
13、 Radiation Units andMeasurements, 7910 Woodmont Ave., Suite 800, Bethesda, MD 20814, U.S.A.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.4 dosimetera device that, when irradiated, exhibits aquantifiable change in some property of
14、the device which canbe related to absorbed dose in a given material using appro-priate analytical instrumentation and techniques.3.5 dosimetry systema system used for determining ab-sorbed dose, consisting of dosimeters, measurementinstruments, and their associated reference standards, andprocedures
15、 for the systems use.3.6 DUTdevice under test. This is the electronic compo-nent or system tested to determine its performance during orafter irradiation.3.7 endpoint energyendpoint energy refers to the peakenergy of the electron beam, usually in MeV, generated in aflash X-ray source and is numerica
16、lly equal to the maximumvoltage in MV. The word endpoint refers to the highest photonenergy of the bremsstrahlung spectra, and this endpoint isequal to the maximum or peak in the electron energy. Forexample, if the most energetic electron that strikes the con-verter is 10 MeV, this electron produces
17、 a range of bremsstrahl-ung photon energies but the maximum energy of any photon isequal to 10 MeV, the endpoint energy. Most photons haveenergies one-tenth to one-third of the maximum electronenergy for typical flash X-ray sources in the 10 MV to 1 MVendpoint voltage region, respectively.3.8 endpoi
18、nt voltageEndpoint voltage refers to the peakvoltage across a bremsstrahlung diode in a flash X-ray source.For example, a 10-MV flash X-ray source is designed to reacha peak voltage of 10-MV across the anode-cathode gap whichgenerates the electron beam for striking a converter to producebremsstrahlu
19、ng.3.9 equilibrium absorbed doseabsorbed dose at someincremental volume within the material in which the conditionof electron equilibrium (the energies, number, and direction ofcharged particles induced by the radiation are constantthroughout the volume) exists. For lower energies wherebremsstrahlun
20、g production is negligible the equilibrium ab-sorbed dose is equal to the kerma.NOTE 1For practical purposes, assuming the spatial gradient in theX-ray field is small over the range of the maximum energy secondaryelectrons generated by the incident photons, the equilibrium absorbeddose is the absorb
21、ed dose value that exists in a material at a distance fromany interface with another material greater than this range.4. Significance and Use4.1 Flash X-ray facilities provide intense bremsstrahlungradiation environments, usually in a single sub-microsecondpulse, which often fluctuates in amplitude,
22、 shape, and spectrumfrom shot to shot. Therefore, appropriate dosimetry must befielded on every exposure to characterize the environment, seeICRU Report 34. These intense bremsstrahlung sources have avariety of applications which include the following:4.1.1 Generation of X-ray and gamma-ray environm
23、entssimilar to that from a nuclear weapon burst.4.1.2 Studies of the effects of X-rays and gamma rays onmaterials.4.1.3 Studies of the effects of radiation on electronic devicessuch as transistors, diodes, and capacitors.4.1.4 Vulnerability and survivability testing of militarysystems and components
24、.4.1.5 Computer code validation studies.4.2 This guide is written to assist the experimenter inselecting the needed dosimetry systems (not all radiationparameters must be measured in a given experiment) for use atpulsed X-ray facilities. This guide also provides a briefsummary of the information on
25、how to use each of thedosimetry systems. Other guides (see Section 2) provide moredetailed information on selected dosimetry systems in radiationenvironments and should be consulted after an initial decisionis made on the appropriate dosimetry system to use. There aremany key parameters which descri
26、be a flash X-ray source, suchas dose, dose rate, spectrum, pulse width, etc., such thattypically no single dosimetry system can measure all theparameters simultaneously.5. General Characteristics of Flash X-ray Sources5.1 Flash X-ray Facility ConsiderationsFlash X-raysources operate like a dental X-
27、ray source but at much highervoltages and intensities and usually in a single, very shortburst, see ICRU Report 17. A high voltage is developed acrossan anode-cathode gap (the diode) and field emission creates apulsed electron beam traveling from the cathode to the anode.A high atomicnumber element
28、such as tantalum is placed onthe anode to maximize the production of bremsstrahlungcreated when the electrons strike the anode. Graphite oraluminum is usually placed downstream of the converter tostop the electron beam completely but let the X-radiation passthrough. Finally, a debris shield made of
29、Kevlar or low-densitypolyethylene is sometimes necessary to stop exploding con-verter material from leaving the source. All of these compo-nents taken together form what is commonly called abremsstrahlung diode.5.2 Relationship Between Flash X-ray Diode Voltage andX-ray Energy of BremsstrahlungFlash
30、 X-ray sources producebremsstrahlung by generating an intense electron beam whichthen strikes a high atomic number (Z) converter such astantalum. The electron-solid interactions produce “braking”radiation or, in German, bremsstrahlung. Fig. 1 shows thetypical range of photon energies produced by thr
31、ee differentsources. If the average radiation produced is in the 20100 keVregion, the source is said to be a mediumhard X-ray simulator.If the average photon energy is in the 100300keV region, theterm used is “hard X-ray simulator.” At the high end of theflash X-ray range are sources which produce a
32、n average photonenergy of around 2 MeV. Because this photon energy is in thetypical gamma-ray spectral range, the source is called agamma-ray simulator.5.2.1 The average energy of the bremsstrahlung spectrum,Ephoton, through an optimized converter (1)4in the medium-hard X-ray region (50 keV 500 keV)
33、 is givenempirically by,Ephoton5 1/2(4)where Ephotonis the average energy of the bremsstrahlung4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.E1894 132photons in keV and is the average energy of the electronsin the electron beam incident on the conver
34、ter in keV. Thisequation and Fig. 1 indicate that most of the photons haveenergies much less than the endpoint electron energy, or involtage units, the flash X-ray voltage.6. Measurement Principles6.1 Typically in flash X-ray irradiations, one is interested insome physical change in a critical regio
35、n of a device under test(DUT). The dosimetry associated with the study of such aphysical change may be broken into three parts:6.1.1 Determine the absorbed dose in a dosimeter.6.1.2 Using the dosimeter measurement, estimate the ab-sorbed dose in the region and material of interest in the DUT.6.1.3 I
36、f required, relate the estimated absorbed dose in theDUT to the physical change of interest (holes trapped, interfacestates generated, photocurrent produced, etc.)6.2 This section will be concerned with the first two of theabove listed parts of dosimetry: (1) what is necessary todetermine a meaningf
37、ul absorbed dose for the dosimeter and(2) what is necessary to extrapolate this measured dose to theestimated dose in the region of interest. The final step indosimetry, associating the absorbed dose with a physicalchange of interest, is outside the scope of this guide.6.3 Energy Deposition:6.3.1 Se
38、condary ElectronsBoth in the case of absorbeddose in the DUT and absorbed dose in the dosimeter, theenergy is deposited largely by secondary electrons. That is, theincident photons interact with the material of, or surrounding,the DUT or the dosimeter and lose energy to Comptonelectrons, photoelectr
39、ons, and Auger electrons. The energywhich is finally deposited in the material is deposited by thesesecondary particles.6.3.2 Transport of PhotonsIn some cases, it is necessaryto consider the transport and loss of photons as they move tothe region whose absorbed dose is being determined. Acorrection
40、 for the attenuation of an incident photon beam is anexample of such a consideration.6.3.3 Transport of ElectronsElectron transport may causeenergy originally imparted to electrons in one region to becarried to a second region depending on the range of theelectrons. As a result, it is necessary to c
41、onsider the transportand loss of electrons as they move into and out of the regionswhose absorbed dose is being determined. In particular, it isnecessary to distinguish between equilibrium and non-equilibrium conditions for electron transport.6.3.3.1 Charged Particle EquilibriumIn some cases, thenum
42、bers, energies, and angles of particles transported into aregion of interest are approximately balanced by those trans-ported out of that region. Such cases form an important class oflimiting cases which are particularly easy to interpret. (See“Equilibrium Absorbed Dose” in 3.9.)6.3.3.2 Dose Enhance
43、mentBecause photoelectron pro-duction per atom is roughly proportional to the atomic numberraised to the fourth power for energies less than 100 keV (2),one expects more photoelectrons to be produced in high atomicnumber layers than in low atomic number layers for the samephoton fluence and spectrum
44、. Thus, there may be a net flow ofenergetic electrons from the high atomic number layers into thelow atomic number layers. This nonequilibrium flow ofelectrons may result in an enhancement of the dose in the lowatomic number layer. Dose enhancement problems are oftencaused by high atomic number bond
45、ing layers (for example,gold), and metallization layers (for example, WSi or TaSi).6.4 Absorbed Dose in Dosimeter:6.4.1 Equilibrium Absorbed Dose in Dosimeter:FIG. 1 Range of Available Bremsstrahlung Spectra from Flash X-ray SourcesE1894 1336.4.1.1 It is frequently possible to use dosimeters underap
46、proximate equilibrium conditions. The interpretation of theoutput of the dosimeter is straightforward only when theenergy deposition processes within the dosimeter are approxi-mately in equilibrium. That is, when the absorbed dose withinthe dosimeter is an equilibrium absorbed dose.6.4.1.2 It is pos
47、sible to treat nonequilibrium energy depo-sition within a dosimeter, but such an analysis requires electronand photon transport calculations, often in the form of com-puter codes.6.4.2 Limiting Cases:6.4.2.1 There are two limiting cases for which the dosimeterdata can be analyzed in a straightforwar
48、d manner.6.4.2.2 Limiting Case One: Short Electron Range:(1) For this case, secondary electron ranges are small incomparison with the size of the dosimeter.(2) Essentially all electrons which deposit energy withinthe dosimeter will be produced within the dosimeter.(3) Non-equilibrium effects due to
49、electron transport arenegligible, but photon attenuation corrections may be neces-sary.(4) An example of this limiting case would be 20 keVphotons depositing energy in a typical (0.889 mm thick)thermoluminescence (TL) dosimeter (TLD). In this case, thesecondary electrons have ranges which are small in comparisonwith the size of the TLdosimeter.As a result, it is not necessaryto perform a correction for the effect of electron transport onabsorbed dose. On the other hand, 20 keV photons may besignificantly attenuated while traveling through a TL
