1、Designation: E1894 13aE1894 18Standard 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
2、of last revision. 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 using dosimetry systems in flash X-ray experiments. Both dose and d
3、ose-ratetechniques are described.1.2 Operating characteristics of flash X-ray sources are given, with emphasis on the spectrum of the photon output.1.3 Assistance is provided to relate the measured dose to the response of a device under test (DUT). The device is assumed tobe a semiconductor electron
4、ic part or system.1.4 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Techni
5、cal Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E170 Terminology Relating to Radiation Measurements and DosimetryE666 Practice for Calculating Absorbed Dose From Gamma or X RadiationE668 Practice for Application of Thermoluminescence-Dosimetry (TLD) Systems for Deter
6、mining Absorbed Dose inRadiation-Hardness Testing of Electronic DevicesE1249 Practice for Minimizing Dosimetry Errors in Radiation Hardness Testing of Silicon Electronic Devices Using Co-60Sources2.2 ISO/ASTM Standards:3ISO/ASTM 51261 Practice for Calibration of Routine Dosimetry Systems for Radiati
7、on ProcessingISO/ASTM 51275 Practice for Use of a Radiochromic Film Dosimetry SystemISO/ASTM 51310 Practice for Use of a Radiochromic Optical Waveguide Dosimetry System2.3 International Commission on Radiation Units (ICRU) and Measurements Reports:4ICRU Report 14 Radiation Dosimetry: X rays and Gamm
8、a Rays with Maximum Photon Energies Between 0.6 and 50 MeVICRU Report 17 Radiation Dosimetry: X rays Generated at Potentials of 5 to 150 kVICRU Report 34 The Dosimetry of Pulsed RadiationICRU Report 51 Quantities and Units in Radiation Protection DosimetryICRU Report 60 Fundamental Quantities and Un
9、its for Ionizing RadiationICRU Report 76 Measurement Quality Assurance for Ionizing Radiation DosimetryICRU Report 77 Elastic Scattering of Electrons and PositronsICRU Report 80 Dosimetry Systems for Use in Radiation ProcessingICRU Report 85a Fundamental Quantities and Units for Ionizing Radiation1
10、This practice is under the jurisdiction of ASTM Committee E10 on Nuclear Technology and Applications and is the direct responsibility of Subcommittee E10.07 onRadiation Dosimetry for Radiation Effects on Materials and Devices.Current edition approved Aug. 1, 2013Dec. 1, 2018. Published September 201
11、3December 2018. Originally approved in 1997. Last previous edition approved in 2013 asE1894 13.E1894 13a. DOI: 10.1520/E1894-13A.10.1520/E1894-18.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standards
12、volume information, refer to the standards Document Summary page on the ASTM website.3 For referenced ISO/ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Su
13、mmary page on the ASTM website.4 Available from the International Commission on Radiation Units and Measurements, 7910 Woodmont Ave., Suite 800, Bethesda, MD 20814, U.S.A.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes
14、have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official
15、document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13. Terminology3.1 absorbed dosequotient of d/dm, where d is the mean energy imparted by ionizing radiation to matter of mass dm:D 5 ddm (1)See ICRU Report 85a. The special name
16、for the unit for absorbed dose is the gray (Gy).1Gy51J/kg (2)Formerly, the special unit for absorbed dose was the rad, where 1 rad = 100 erg/g.1rad50.01 Gy (3)Since the absorbed dose due to a given radiation field is material dependent, it is important to include the material compositionfor which th
17、e dose is being reported, e.g., 15.3 Gy(LiF).3.1 absorbed dose enhancementincrease (or decrease) in the absorbed dose (as compared to the equilibrium absorbed dose)at a point in a material of interest. This can be expected to occur near an interface with a material of higher or lower atomic number.3
18、.2 convertera target for electron beams, generally of a high atomic number material, in which bremsstrahlung X-rays areproduced by radiative energy losses of the incident electrons.3.4 dosimetera device that, when irradiated, exhibits a quantifiable change in some property of the device which can be
19、 relatedto absorbed dose in a given material using appropriate analytical instrumentation and techniques.3.3 dosimetry systema system used for determining absorbed dose, consisting of dosimeters, measurement instruments, andtheir associated reference standards, and procedures for the systems use.3.4
20、 DUTdevice under test. This is the electronic component or system tested to determine its performance during or afterirradiation.3.5 endpoint energyendpoint energy refers to the peak energy of the electron beam, usually in MeV, generated in a flash X-raysource and is numerically equal to the maximum
21、 voltage in MV. The word endpoint refers to the highest photon energy of thebremsstrahlung spectra, and this endpoint is equal to the maximum or peak in the electron energy. For example, if the mostenergetic electron that strikes the converter is 10 MeV, this electron produces a range of bremsstrahl
22、ung photon energies but themaximum energy of any photon is equal to 10 MeV, the endpoint energy. Most photons have energies one-tenth to one-third ofthe maximum electron energy for typical flash X-ray sources in the 10 MV to 1 MV endpoint voltage region, respectively.3.6 endpoint voltageEndpoint vol
23、tage refers to the peak voltage across a bremsstrahlung diode in a flash X-ray source. Forexample, a 10-MV flash X-ray source is designed to reach a peak voltage of 10-MV across the anode-cathode gap which generatesthe electron beam for striking a converter to produce bremsstrahlung.3.7 equilibrium
24、absorbed doseabsorbed dose at some incremental volume within the material in which the condition ofelectron equilibrium (the energies, number, and direction of charged particles induced by the radiation are constant throughout thevolume) exists. For lower energies where bremsstrahlung production is
25、negligible the equilibrium absorbed dose is equal to thekerma.NOTE 1For practical purposes, assuming the spatial gradient in the X-ray field is small over the range of the maximum energy secondary electronsgenerated by the incident photons, the equilibrium absorbed dose is the absorbed dose value th
26、at exists in a material at a distance from any interface withanother material greater than this range.4. Significance and Use4.1 Flash X-ray facilities provide intense bremsstrahlung radiation environments, usually in a single sub-microsecond pulse,which often fluctuates in amplitude, shape, and spe
27、ctrum from shot to shot. Therefore, appropriate dosimetry must be fielded onevery exposure to characterize the environment, see ICRU Report 34. These intense bremsstrahlung sources have a variety ofapplications which include the following:4.1.1 Generation of X-ray and gamma-ray environments similar
28、to that from a nuclear weapon burst.4.1.1 Studies of the effects of X-rays and gamma rays on materials.4.1.2 Studies of the effects of radiation on electronic devices such as transistors, diodes, and capacitors.4.1.4 Vulnerability and survivability testing of military systems and components.4.1.3 Co
29、mputer code validation studies.4.2 This guide is written to assist the experimenter in selecting the needed dosimetry systems (not all radiation parameters mustbe measured in a given experiment) for use at pulsed X-ray facilities. This guide also provides a brief summary of the informationon how to
30、use each of the dosimetry systems. Other guides (see Section 2) provide more detailed information on selected dosimetrysystems in radiation environments and should be consulted after an initial decision is made on the appropriate dosimetry systemto use. There are many key parameters which describe a
31、 flash X-ray source, such as dose, dose rate, spectrum, pulse width, etc.,E1894 182such that typically no single dosimetry system can measure all the parameters simultaneously. However, it is frequently the casethat not all key parameters must be measured in a given experiment.5. General Characteris
32、tics of Flash X-ray Sources5.1 Flash X-ray Facility ConsiderationsFlash X-ray sources operate like a dental X-ray source but at much higher voltagesand intensities and usually in a single, very short burst, see ICRU Report 17.Ahigh voltage is developed across an anode-cathodegap (the diode) and fiel
33、d emission creates a pulsed electron beam traveling from the cathode to the anode. A high atomicnumberelement such as tantalum is placed on the anode to maximize the production of bremsstrahlung created when the electrons strikethe anode. Graphite or aluminum is usually placed downstream of the conv
34、erter to stop the electron beam completely but let theX-radiation pass through. Finally, a debris shield made of Kevlar or low-density polyethylene is sometimes necessary to stopexploding converter material from leaving the source. All of these components taken together form what is commonly called
35、abremsstrahlung diode.5.2 Relationship Between Flash X-ray Diode Voltage and X-ray Energy of BremsstrahlungFlash X-ray sources producebremsstrahlung by generating an intense electron beam which then strikes a high atomic number (Z) converter such as tantalum.The electron-solid interactions produce “
36、braking” radiation or, in German, bremsstrahlung. Fig. 1 shows the typical range ofphoton energies produced by three different sources. If the average radiation produced is in the 20100 keV region, the source issaid to be a mediumhard X-ray simulator. If the average photon energy is in the 100300keV
37、 100 300 keV region, the termused is “hard X-ray simulator.” At the high end of the flash X-ray range are sources which produce an average photon energy ofaround 2 MeV. Because this photon energy is in the typical gamma-ray spectral range, the source is called a gamma-ray simulator.5.2.1 The average
38、 energy of the bremsstrahlung spectrum, Ephoton , through an optimized converter can be estimated using thefollowing relationship (1)5 in the medium-hard X-ray region (50 keV 500 keV) is given empirically by,Ephoton 51/2 (1)E photon 5k= where 5.1,k,18.9 (1)where Ephoton is the average energy of the
39、bremsstrahlung photons in keV and is the average energy of the electrons in theelectron beam incident on the converter in keV. The value of k depends on the converter thickness: thin targets will have val-ues at the lower end of the range while thick targets optimized for higher incident energies wi
40、ll have values at the upper end.When an optimized bremsstrahlung converter is used, a rule-of-thumb may be used that the average photon energy is about 15or 16 of the electron endpoint energy (1). For a fixed converter design, the photon energy away from the optimization point isroughly proportional
41、 to the square root of the electron endpoint energy with the proportionality factor varying between about 5and 19 depending upon the design point (1). This equation and Fig. 1 indicate that most of the photons have energies muchless than the endpoint electron energy, or in voltage units, the flash X
42、-ray voltage. Additionally, the bremsstrahlung spectrumis very non-Gaussian so caution must be exercised in using the average energy of the distribution for dosimetry planning.5 The boldface numbers in parentheses refer to the list of references at the end of this standard.FIG. 1 Range of Available
43、Bremsstrahlung Spectra from Flash X-ray SourcesE1894 1836. Measurement Principles6.1 Typically in flash X-ray irradiations, one is interested in some physical change in a critical region of a device under test(DUT). The dosimetry associated with the study of such a physical change may be broken into
44、 three parts:6.1.1 Determine the absorbed dose in a dosimeter.6.1.2 Using the dosimeter measurement, estimate the absorbed dose in the region and material of interest in the DUT.6.1.3 If required, relate the estimated absorbed dose in the DUT to the physical change of interest (holes trapped, interf
45、ace statesgenerated, photocurrent produced, etc.)6.2 This section will be concerned with the first two of the above listed parts of dosimetry: (1) what is necessary to determinea meaningful absorbed dose for the dosimeter and (2) what is necessary to extrapolate this measured dose to the estimated d
46、osein the region of interest. The final step in dosimetry, associating the absorbed dose with a physical change of interest, is outsidethe scope of this guide.6.3 Energy Deposition:6.3.1 Secondary ElectronsBoth in the case of absorbed dose in the DUT and absorbed dose in the dosimeter, the energy is
47、deposited largely by secondary electrons. That is, the incident photons interact with the material of, or surrounding, the DUT orthe dosimeter and lose energy to Compton electrons, photoelectrons, and Auger electrons. The energy which is finally depositedin the material is deposited by these seconda
48、ry particles.6.3.2 Transport of PhotonsIn some cases, it is necessary to consider the transport and loss of photons as they move to theregion whose absorbed dose is being determined.Acorrection for the attenuation of an incident photon beam is an example of sucha consideration.6.3.3 Transport of Ele
49、ctronsElectron transport may cause energy originally imparted to electrons in one region to be carriedto a second region depending on the range of the electrons.As a result, it is necessary to consider the transport and loss of electronsas they move into and out of the regions whose absorbed dose is being determined. In particular, it is necessary to distinguishbetween equilibrium and non-equilibrium conditions for electron transport.6.3.3.1 Charged Particle EquilibriumIn some cases, the numbers, energies, and angles of particles tra
