1、Designation: E 1894 08Standard Guide forSelecting Dosimetry Systems for Application in PulsedX-Ray Sources1This standard is issued under the fixed designation E 1894; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、 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 usingdosimetry systems in flash X-ray experiments. Both dose anddose-rate
3、techniques 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
4、 system.2. Contents2.1 Section 1: Scope of guide.2.2 Section 2: Outline.2.3 Section 3: Related ASTM and ICRU documents.2.4 Section 4: Definition of terms.2.5 Section 5: Significance and use of this document for theselection of dosimetry systems for use in pulsed x-ray sources.2.6 Section 6: Descript
5、ion of large flash x-ray sources andtheir characteristics.2.7 Section 7: Measurement principles with an emphasis onobtaining absorbed dose measurements for different spectralconditions in the dosimeter, the DUT, and the relationshipbetween them.2.8 Section 8: The primary information in this guide. T
6、heexperimenter will find details on each dosimetry system. Listedare details such as: 1) how the dosimeters works, i.e., physicalprinciples, 2) typical applications or instrumentation configu-rations, 3) advantages, 4) limitations, 5) sensitivity 6) proce-dures for calibration and proper use and fin
7、ally reproducibilityand accuracy.2.9 Section 9: Suggested documentation requirements.2.10 Section 10: Description of how the experimenter de-termines uncertainty in the dosimetry measurements.2.11 Section 11: References.3. Referenced Documents3.1 ASTM Standards:2E 170 Terminology Relating to Radiati
8、on Measurementsand DosimetryE 665 Practice for Determining Absorbed Dose VersusDepth in Materials Exposed to the X-ray Output of FlashX-ray Machines3E 666 Practice for Calculating Absorbed Dose FromGamma or X RadiationE 668 Practice for Application of Thermoluminescence-Dosimetry (TLD) Systems for D
9、eterminingAbsorbed Dosein Radiation-Hardness Testing of Electronic DevicesE 1249 Practice for Minimizing Dosimetry Errors in Radia-tion Hardness Testing of Silicon Electronic Devices UsingCo-60 SourcesE 1261 Guide for Selection and Calibration of DosimetrySystems for Radiation Processing3E 1275 Prac
10、tice for Use of a Radiochromic Film DosimetrySystem3E 1310 Practice for Use of a Radiochromic OpticalWaveguide Dosimetry System33.2 International Commission on Radiation Units (ICRU)and Measurements Reports:4ICRU Report 14 Radiation Dosimetry: X rays and GammaRays with Maximum Photon Energies Betwee
11、n 0.6 and 50MeVICRU Report 17 Radiation Dosimetry: X rays Generated atPotentials of 5 to 150 kV1This practice is under the jurisdiction of ASTM Committee E10 on NuclearTechnology and Applications and is the direct responsibility of SubcommitteeE10.07 on Radiation Dosimetry for Radiation Effects on M
12、aterials and Devices.Current edition approved Sept. 15, 2008. Published November 2008. Originallyapproved in 1997. Last previous edition approved in 2002 as E 1894 97 (2002).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For
13、Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.4Available from the International Commission on Radiation Units and Measure-ments, 7910 Wood
14、mont Ave., Suite 800, Bethesda, MD 20814, U.S.A.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.ICRU Report 33 Radiation Quantities and UnitsICRU Report 34 The Dosimetry of Pulsed Radiation4. Terminology4.1 absorbed dosequotient of d
15、e/dm, where de is themean energy imparted by ionizing radiation to matter of massdm: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)Because
16、 the magnitude of the absorbed dose is materialdependent, it is important to include the material compositionfor which the dose is being reported, e.g., 15.3 Gy(LiF).4.2 absorbed dose enhancementincrease (or decrease) inthe absorbed dose (as compared to the equilibrium absorbeddose) at a point in a
17、material of interest. This can be expectedto occur near an interface with a material of higher or loweratomic number.4.3 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.4
18、.4 dosimetera device that, when irradiated, exhibits aquantifiable change in some property of the device which canbe related to absorbed dose in a given material using appro-priate analytical instrumentation and techniques.4.5 dosimetry systemA system used for determining ab-sorbed dose, consisting
19、of dosimeters, measurement instru-ments, and their associated reference standards, and proceduresfor the systems use.4.6 DUTdevice under test. This is the electronic compo-nent or system tested to determine its performance during orafter irradiation.4.7 endpoint energyendpoint energy refers to the p
20、eakenergy of the electron beam, usually in MeV, generated in aflash X-ray source and is numerically 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. Forexamp
21、le, if the most energetic electron that strikes the con-verter is 10 MeV, this electron produces 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
22、typical flash X-ray sources in the 10 MV to 1 MVendpoint voltage region, respectively.4.8 endpoint 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 an
23、ode-cathode gap whichgenerates the electron beam for striking a converter to producebremsstrahlung.4.9 equilibrium absorbed doseabsorbed dose at someincremental volume within the material in which the conditionof electron equilibrium (the energies, number, and direction ofcharged particles induced b
24、y the radiation are constantthroughout the volume) exists. For lower energies wherebremsstrahlung 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
25、secondaryelectrons generated by the incident photons, the equilibrium absorbeddose is the absorbed dose value that exists in a material at a distance fromany interface with another material greater than this range.5. Significance and Use5.1 Flash X-ray facilities provide intense bremsstrahlungradiat
26、ion environments, usually in a single sub-microsecondpulse, which unfortunately, often fluctuates in amplitude,shape, and spectrum from shot to shot. Therefore, appropriatedosimetry must be fielded on every exposure to characterizethe environment, see ICRU Report 34. These intensebremsstrahlung sour
27、ces have a variety of applications whichinclude the following:5.1.1 Generation of X-ray and gamma-ray environmentssimilar to that from a nuclear weapon burst.5.1.2 Studies of the effects of X rays and gamma rays onmaterials.5.1.3 Studies of the effects of radiation on electronic devicessuch as trans
28、istors, diodes, and capacitors.5.1.4 Vulnerability and survivability testing of militarysystems and components.5.1.5 Computer code validation studies.5.2 This guide is written to assist the experimenter inselecting the needed dosimetry systems (often in an experimentnot all radiation parameters must
29、 be measured) for use atpulsed X-ray facilities. This guide also provides a briefsummary of the information on how to use each of thedosimetry systems. Other guides (see Section 3) provide moredetailed information on selected dosimetry systems in radiationenvironments and should be consulted after a
30、n initial decisionis made on the appropriate dosimetry system to use. There aremany key parameters which describe a flash X-ray source, suchas dose, dose rate, spectrum, pulse width, etc., such thattypically no single dosimetry system can measure all theparameters simultaneously.6. General Character
31、istics of Flash X-ray Sources6.1 Flash X-ray Facility ConsiderationsFlash X-raysources operate like a dental X-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 fi
32、eld emission creates apulsed electron beam traveling from the cathode to the anode.A high atomicnumber element 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 conve
33、rter tostop the electron beam completely but let the X-radiation passthrough. Finally, a debris shield made of Kevlar or low-densityE1894082polyethylene is sometimes necessary to stop exploding con-verter material from leaving the source. All of these compo-nents taken together form what is commonly
34、 called abremsstrahlung diode.6.2 Relationship Between Flash X-ray Diode Voltage andX-ray Energy of BremsstrahlungFlash X-ray sources pro-duce bremsstrahlung by generating an intense electron beamwhich then strikes a high atomic number (Z) converter such astantalum. The electron-solid interactions p
35、roduce “braking”radiation or, in German, bremsstrahlung. Fig. 1 shows thetypical range of photon energies produced by three 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 1003
36、00keV region, theterm used is “hard X-ray simulator.” At the high end of theflash X-ray range are sources which produce an average photonenergy of around 2 MeV. Because this photon energy is in thetypical gamma-ray spectral range, the source is called agamma-ray simulator.6.2.1 The average energy of
37、 the bremsstrahlung spectrum,Ephoton, through an optimized converter (1)5in the medium-hard X-ray region (50 keV 500 keV) is givenempirically by,Ephoton 5 1/2(4)where Ephotonis the average energy of the bremsstrahlungphotons in keV and is the average energy of the electrons inthe electron beam incid
38、ent on the converter 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.7. Measurement Principles7.1 Typically in flash X-ray irradiations, one is interested insome physical change in
39、 a critical region of a device under test(DUT). The dosimetry associated with the study of such aphysical change may be broken into three parts:7.1.1 Determine the absorbed dose in a dosimeter.7.1.2 Using the dosimeter measurement, estimate the ab-sorbed dose in the region and material of interest i
40、n the DUT.7.1.3 If required, relate the estimated absorbed dose in theDUT to the physical change of interest (holes trapped, interfacestates generated, photocurrent produced, etc.)7.2 This section will be concerned with the first two of theabove listed parts of dosimetry: (1) what is necessary todet
41、ermine a meaningful 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.7.3 Energy De
42、position:7.3.1 Secondary 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 Comptonelect
43、rons, photoelectrons, and Auger electrons. The energywhich is finally deposited in the material is deposited by thesesecondary particles.7.3.2 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 determ
44、ined. Acorrection for the attenuation of an incident photon beam is anexample of such a consideration.7.3.3 Transport of ElectronsElectron transport may causeenergy originally imparted to electrons in one region to be5The boldface numbers in parentheses refer to the list of references at the end oft
45、his standard.FIG. 1 Range of Available Bremsstrahlung Spectra from Flash X-ray SourcesE1894083carried to a second region depending on the range of theelectrons. As a result, it is necessary to consider the transportand loss of electrons as they move into and out of the regionswhose absorbed dose is
46、being determined. In particular, it isnecessary to distinguish between equilibrium and non-equilibrium conditions for electron transport.7.3.3.1 Charged Particle EquilibriumIn some cases, thenumbers, energies, and angles of particles transported into aregion of interest are approximately balanced by
47、 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 Section 4.6.)7.3.3.2 Dose EnhancementBecause photoelectron pro-duction per atom is roughly proportional to the atomic numberraised
48、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. Thus, there may be a net flow ofenergetic electrons from the high atomic number layers into thel
49、ow 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 bonding layers (e.g., gold), andmetallization layers (e.g., WSi or TaSi).7.4 Absorbed Dose in Dosimeter:7.4.1 Equilibrium Absorbed Dose in Dosimeter:7.4.1.1 It is frequently possible to use dosimeters underapproximately equilibrium conditions. The interpretation of theoutput of the dosimeter is straightforward only when theenergy deposition processes wi
