1、Designation: E265 07 (Reapproved 2013)Standard Test Method forMeasuring Reaction Rates and Fast-Neutron Fluences byRadioactivation of Sulfur-321This standard is issued under the fixed designation E265; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、 case of revision, the year 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.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This t
3、est method describes procedures for measuringreaction rates and fast-neutron fluences by the activationreaction32S(n,p)32P.1.2 This activation reaction is useful for measuring neutronswith energies above approximately 3 MeV.1.3 With suitable techniques, fission-neutron fluences fromabout 5 108to 101
4、6n/cm2can be measured.1.4 Detailed procedures for other fast-neutron detectors aredescribed in Practice E261.1.5 This standard does not purport to address all of thesafety problems, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety
5、 and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E170 Terminology Relating to Radiation Measurements andDosimetryE181 Test Methods for Detector Calibration and Analysis ofRadionuclidesE261 Practice for Determinin
6、g Neutron Fluence, FluenceRate, and Spectra by Radioactivation TechniquesE720 Guide for Selection and Use of Neutron Sensors forDetermining Neutron Spectra Employed in Radiation-Hardness Testing of ElectronicsE721 Guide for Determining Neutron Energy Spectra fromNeutron Sensors for Radiation-Hardnes
7、s Testing of Elec-tronicsE844 Guide for Sensor Set Design and Irradiation forReactor Surveillance, E 706 (IIC)E944 Guide for Application of Neutron Spectrum Adjust-ment Methods in Reactor Surveillance, E 706 (IIA)E1018 Guide for Application of ASTM Evaluated CrossSection Data File, Matrix E706 (IIB)
8、3. Terminology3.1 Definitions:3.1.1 Refer to Terminology E170.4. Summary of Test Method4.1 Elemental sulfur or a sulfur-bearing compound is irra-diated in a neutron field, producing radioactive32P by means ofthe32S(n,p)32P activation reaction.4.2 The beta particles emitted by the radioactive decay o
9、f32Pare counted by techniques described in Methods E181 andthe reaction rate, as defined in Practice E261, is calculated fromthe decay rate and irradiation conditions.4.3 The neutron fluence above 3 MeV can then be calcu-lated from the spectral-averaged neutron activation crosssection, , as defined
10、in Practice E261.5. Significance and Use5.1 Refer to Guides E720 and E844 for the selection,irradiation, and quality control of neutron dosimeters.5.2 Refer to Practice E261 for a general discussion of thedetermination of fast-neutron fluence and fluence rate withthreshold detectors.5.3 The activati
11、on reaction produces32P, which decays bythe emission of a single beta particle in 100 % of the decays,and which emits no gamma rays. The half life of32P is 14.262(14)3days (1)4and the maximum beta energy is 1710 keV (2).1This test method is under the jurisdiction ofASTM Committee E10 on NuclearTechn
12、ology and Applicationsand is the direct responsibility of SubcommitteeE10.07 on Radiation Dosimetry for Radiation Effects on Materials and Devices.Current edition approved Jan. 1, 2013. Published January 2013. Originallyapproved in 1970. Last previous edition approved in 2007 as E265 071. DOI:10.152
13、0/E0265-07R13.2For 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.3The non-bolface number in parentheses after th
14、e nuclear data indicates theuncertainty in the last significant digit of the preceding number. For example, 8.1 s(5) means 8.1 6 0.5 seconds.4The boldface numbers in parentheses refer to the list of references at the end ofthis test method.Copyright ASTM International, 100 Barr Harbor Drive, PO Box
15、C700, West Conshohocken, PA 19428-2959. United States15.4 Elemental sulfur is readily available in pure form andany trace contaminants present do not produce significantamounts of radioactivity. Natural sulfur, however, is composedof32S (95.02 % (9),34S (4.21 % (8) (1), and trace amounts ofother sul
16、fur isotopes.The presence of these other isotopes leadsto several competing reactions that can interfere with thecounting of the 1710-keV beta particle. This interference canusually be eliminated by the use of appropriate techniques, asdiscussed in Section 8.6. Apparatus6.1 Since only beta particles
17、 of32P are counted, propor-tional counters or scintillation detectors can be used. Becauseof the high resolving time associated with Geiger-Muellercounters, their use is not recommended. They can be used onlywith relatively low counting rates, and then only if reliablecorrections for coincidence los
18、ses are applied.6.2 Refer to Methods E181 for preparation of apparatus andcounting procedures.7. Materials and Manufacture7.1 Commercially available sublimed flowers of sulfur areinexpensive and sufficiently pure for normal usage. Sulfur canbe used directly as a powder or pressed into pellets. Sulfu
19、rpellets are normally made at least 3 mm thick in order to obtainmaximum counting sensitivity independent of small variationsin pellet mass. A 0.8 g/cm2pellet can be considered infinitelythick for the most energetic beta particle from32P(see Table 1).Due to the relatively long half-life of32P, it ma
20、y not bepractical to use a pellet more than once.Aperiod of at least oneyear is recommended between uses. However, see 8.2 regard-ing long-lived interfering reaction products.7.2 Where temperatures approaching the melting point ofsulfur are encountered (113C), sulfur-bearing compoundssuch as ammoniu
21、m sulfate (NH4)2SO4, lithium sulfate Li2SO4,or magnesium sulfate MgSO4can be used. These are suitablefor temperatures up to 250, 850, and 1000C, respectively. Thereduced sensitivity of these compounds offers no disadvantagesince high temperatures are usually associated with a high-neutron fluence ra
22、te. The sulfur content by weight of(NH4)2SO4is 24 %, of Li2SO4is 29.2 %, and of MgSO4is26.6 %.7.3 The isotopic abundance of32S in natural sulfur is 95.026 0.09 atom % (1).8. Sample Preparation and Irradiation8.1 Place sulfur in pellet or powdered form in a uniformfast-neutron flux for a predetermine
23、d period of time. Recordthe beginning and end of the irradiation period.8.2 Table 2 lists competing reaction products that must beeliminated from the counting. Those resulting from thermal-neutron capture, that is,33P,35S, and37S, can be reduced by theirradiation of the sulfur inside 1 mm-thick cadm
24、ium shields.This should be done whenever possible in thermal-neutronenvironments. Those reaction products having relatively shorthalf-lives, that is,31S,34P,31Si, and37S, can be eliminated bya waiting period before the counting is started. A delay of 24 his sufficient for the longest lived of these,
25、 although shorterdelays are possible depending on the degree of thermalizationof the neutron field. Finally, those with relatively low betaparticle energies, that is,33P and35S, can be eliminated by theinclusion of a 70-mg/cm2aluminum absorber in front of thedetector. For particularly long decay tim
26、es, an absorber must beused because the35S becomes dominant. Note that the use ofan internal (windowless) detector maximizes the interferencein counting from35S.8.3 Irradiated sulfur can be counted directly, or may beburned to increase the efficiency of the counting system.Dilution may be used to re
27、duce counting system efficiency formeasurements of high neutron fluences.8.4 Burning the sulfur leaves a residue of32P that can becounted without absorption of the beta particles in the sulfurpellet. Place the sulfur in an aluminum planchet on a hot plateuntil the sulfur melts and turns to a dark am
28、ber color. At thispoint the liquid gives off sulfur fumes. Ignite the fumes bybringing a flame close to the dish, and allow the sulfur to burnout completely. In order to reduce the sputtering that can leadto variations in the amount of32P remaining on the planchet,the hot plate must be only as hot a
29、s necessary to melt the sulfur.In addition, air flow to the burning sulfur must be controlled,such as by the placement of a chimney around the sulfur. Countthe residue remaining on the dish for beta activity.NOTE 1The fumes given off by the burning sulfur are toxic. Burningshould be done under a ven
30、tilating hood.8.5 An alternative to burning is sublimation of the sulfurunder a heat lamp. Removal of the sulfur is very gradual, andthere is no loss of32P from sputtering.8.6 Counting of dilute samples is useful for measuring highneutron fluences, although it is applicable to virtually allirradiati
31、on conditions. Use lithium sulfate, reagent grade orbetter, as the target material because of its high melting point(860C), good solubility in water, and minimum production ofundesirable activation products. Prepare a dry powder byspreading about 10 g of Li2SO4in a weighing bottle and placeTABLE 1 S
32、ulfur Counting Rate Versus Mass for a Pellet of25.4-mm DiameterSample Mass, g Relative Counting Rate0.4 0.460.6 0.580.8 0.661.0 0.731.2 0.781.4 0.821.6 0.861.8 0.892.0 0.912.2 0.932.4 0.942.6 0.952.8 0.963.0 0.973.2 0.983.4 0.993.6 0.993.8 1.04.0 1.0E265 07 (2013)2in a drying oven for 24 h at 150C.
33、Place the dried Li2SO4ina dessicator for cooling and storage. Prepare a phosphoruscarrier solution by dissolving 21.3 g of (NH4)2HPO4in waterto make 1 L of solution. Prepare a Li2SO4sample forirradiation by placing about 150 mg of material in an air-tightaluminum capsule or other suitable container.
34、 Following theirradiation, accurately weigh a sample of about 100 mg anddissolve in 5 mL of phosphorus carrier solution to minimizeadsorption of32Pon the glass container.Adrop of concentratedHCl may be used to speed solution of the sample. Place thesolution in a volumetric flask and add additional p
35、hosphoruscarrier solution to bring the total volume to 100 mL. Prepare asample for counting by pipetting 0.050 mL of the32P solutiononto a standard planchet and evaporating in air to dryness.Counting procedures and calculations are the same as in othermethods with the exception that an aliquot facto
36、r of 2000 mustbe introduced for the 0.050-mL sample removed from the100-mL flask.9. Calibration9.1 Calibration is achieved by irradiation of sulfur in afast-neutron field of known spectrum and intensity, and mea-suring the resulting32P activity to determine a countingsystems efficiency. This calibra
37、tion is specific for a givendetector system, counting geometry, and sulfur pellet size andmass or sample preparation. It is, however, valid for subse-quent use in measuring activities in any arbitrary spectrum, andtherefore, may be used with activation data from other foils indetermining neutron ene
38、rgy spectra as described in PracticeE721 and Practice E944.9.2235U fission and252Cf spontaneous fission neutronsources of known source strength are available for directfree-field calibrations (3).9.3 Once a sulfur counting system is calibrated, it must bemonitored to ensure that the calibration rema
39、ins valid. Thereare several isotopes that can be used as reference standards forthis monitoring. One is234Pa, having a maximum beta energyof about 2000 keV, comparable to the 1710-keV beta from32P.It is obtained as a daughter of238U, that can be dispersed as apowder in plastic granules and formed to
40、 the shape of astandard pellet. The concentration of238U can be varied toobtain the desired counting rate. Uranium alpha particles canbe prevented from reaching the detector by use of a 7-mg/cm2absorber. Another useful isotope is210Bi that produces betaparticles having a maximum energy of 1161 keV.
41、It is obtainedas a daughter of210Pb, and sources are commercially avail-able.10. Activity and Fluence by Detector Efficiency Method10.1 Using a sulfur sample irradiated in a calibration neu-tron field, determine the efficiency, , for the detector system: 5Cfexptd# tiN s 1 2 exp2tc#!1 2 exp2ti#!(1)wh
42、ere:C = counts recorded in detector, less background,f= correction for coincidence losses, if needed, =32P decay constant, = 5.625 107s1,td= decay time, s,tc= count time, s,ti= duration of irradiation, s,N = number of32S atoms in pellet,s= spectrum-averaged cross section for32S in the calibra-tion n
43、eutron field, cm2=1024b, and = neutron fluence, n/cm2.10.1.1 Fig. 1 shows a plot of sulfur cross section as afunction of energy. Fig. 2 shows a plot of the uncertainty in thesulfur cross section as a function of energy. (See also GuideE1018.) The spectrum-averaged cross section for252Cf fissionneutr
44、ons is about 70 mb, and for235U fission is about 63 mb.(See Table 2 and Refs (4-10).)TABLE 2 Neutron-induced Reactions in Sulfur Giving Radioactive ProductsReactionCross Section Cross Section (mb)ProductHalflife(1)MaximumEnergy ofProductBeta (MeV)(2)AverageEnergy ofProductBeta(MeV) (2)IsotopicAbunda
45、nceofTarget (%)(1)Library Material ID ThermalA235UThermalFissionFastB252CfFission1.32S(n,p)32P GLUCS-93C1625 . 64.69 70.44 14.262d (14)1.7104 0.6949 95.02 (9)2.32S(n,2n)31S JENDL-3D3161 . 7.742 1062.51052.572 s(13)5.3956( +)1.9975( +)95.02 (9)3.33S(n,p)33P JENDL-3D3162 1.6 57.46 58.77 25.34 d(12)0.2
46、485 0.0764 0.75 (1)4.34S(n,P)34P JENDL-3D3163 . 0.8001 1.079 12.43 s(8)5.3743 2.3108 4.21 (8)5.34S(n,)31Si JENDL-3D3163 . 3.281 4.064 157.3 m(3)1.4908 0.59523 4.21 (8)6.34S(n,)35S JENDL-3D3163 226 0.2749 0.2705 87.51 d(12)0.16684 0.04863 4.21 (8)7.36S(n,)37S JENDL-3D3164 151 0.2511 0.2509 5.05 m(2)4
47、.86516 0.800418 0.02 (1)AThe thermal cross section corresponds to neutrons with a velocity of 2200 m/s or energy of 0.0253 eV.BThe fast cross section corresponds to the spectrum-averaged cross section from the ENDF/B-VI (MAT=9228, MF=5, MT=18)235U thermal fission spectrum (5,6) andthe ENDF/B-VI (MAT
48、=9861, MF=5, MT=18)252Cf spontaneous fission spectrum (4-6).CCross section produced for the 1993 GLUCS library (7) and is similar to that in the IRDF-90 library (8).DThe JENDL-3 (9) sulfur isotopes were adopted in the latest JEF 2.2 cross section (10) compilations. The ENDF/B-VI library (5) does not
49、 include the individual sulfurisotopic cross sections.E265 07 (2013)310.1.2 The correction for coincidence losses, f, is a func-tion of the particular counting system, and may be alreadyaccounted for by the system electronics if “live time” is used(see Methods E181). Coincidence loss corrections can be large,especially when Geiger-Mueller counters are used.NOTE 2Because of self-absorption in counting thick pellets intact,detection efficiency is not sensitive to small variations in pellet mass butis rather a function of the pellet
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