1、Designation: E 265 07Standard Test Method forMeasuring Reaction Rates and Fast-Neutron Fluences byRadioactivation of Sulfur-321This standard is issued under the fixed designation E 265; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisio
2、n, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 test method desc
3、ribes 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 3 108to 1016n/cm2can be
4、measured.1.4 Detailed procedures for other fast-neutron detectors aredescribed in Practice E 261.1.5 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 and health
5、practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 170 Terminology Relating to Radiation Measurementsand DosimetryE 181 Test Methods for Detector Calibration and Analysisof RadionuclidesE 261 Practice for Determining Neutron
6、 Fluence, FluenceRate, and Spectra by Radioactivation TechniquesE 720 Guide for Selection and Use of Neutron Sensors forDetermining Neutron Spectra Employed in Radiation-Hardness Testing of ElectronicsE 721 Guide for Determining Neutron Energy Spectra fromNeutron Sensors for Radiation-Hardness Testi
7、ng of Elec-tronicsE 844 Guide for Sensor Set Design and Irradiation forReactor Surveillance, E 706(IIC)E 944 Guide for Application of Neutron Spectrum Adjust-ment Methods in Reactor Surveillance, E 706 (IIA)E 1018 Guide for Application of ASTM Evaluated CrossSection Data File, Matrix E 706 (IIB)3. T
8、erminology3.1 Definitions:3.1.1 Refer to Terminology E 170.4. Summary of Test Method4.1 Elemental sulfur or a sulfur-bearing compound is irra-diated in a neutron field, producing radioactive32Pby means ofthe32S(n,p)32P activation reaction.4.2 The beta particles emitted by the radioactive decay of32P
9、 are counted by techniques described in Methods E 181and the reaction rate, as defined in Practice E 261, is calculatedfrom the 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, s, as defined
10、in Practice E 261.5. Significance and Use5.1 Refer to Guides E 720 and E 844 for the selection,irradiation, and quality control of neutron dosimeters.5.2 Refer to Practice E 261 for a general discussion of thedetermination of fast-neutron fluence and fluence rate withthreshold detectors.5.3 The acti
11、vation 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).5.4 Elemental sulfur is readily available in pure form andany trace contamina
12、nts present do not produce significantamounts of radioactivity. Natural sulfur, however, is composedof32S (95.02 % (9),34S (4.21 % (8) (1), and trace amounts ofother sulfur isotopes.The presence of these other isotopes leadsto several competing reactions that can interfere with the1This test method
13、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, 2007. Published June 2007. Originallyapproved in 1970. La
14、st previous edition approved in 2002 as E 265 98 (2002).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
15、non-bolface number in parentheses after the 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.1Copyright ASTM In
16、ternational, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.counting 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 of32P are count
17、ed, 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 losses are applied.
18、6.2 Refer to Methods E 181 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. Sulfurpellets are no
19、rmally 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(seeTable 1).Due to the relatively long half-life of32P, it may not bepractica
20、l 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 ammonium sulfate (NH4)2
21、SO4, 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 rate. The sulfur c
22、ontent 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 predetermined period of time
23、. 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 cadmium shields.This
24、 should be done whenever possible in thermal-neutronenvironments. Those reaction products having relatively shorthalf-lives, that is,31S,34P,31Si, and37S, can be eliminated by awaiting period before the counting is started.Adelay of 24 h issufficient for the longest lived of these, although shorter
25、delaysare possible depending on the degree of thermalization of theneutron field. Finally, those with relatively low beta particleenergies, that is,33Pand35S, can be eliminated by the inclusionof a 70-mg/cm2aluminum absorber in front of the detector. Forparticularly long decay times, an absorber mus
26、t be usedbecause the35S becomes dominant. Note that the use of aninternal (windowless) detector maximizes the interference incounting 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 reduce counting syste
27、m 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 amber color. At thisp
28、oint 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 as necessary to melt
29、 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 ventilating hood.8.5 A
30、n 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 allirradiation conditions. Use
31、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 placein a drying oven for 24 h at
32、 150C. 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 con
33、tainer. 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 concentratedTABLE 1 Sulfur Counting Rate Versus Mass for a Pellet of25.4-mm DiameterSample Mass, g Relative Counti
34、ng 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 1.0E265072HCl may be used to speed solution of the sample. Place thesolution in a volumetric flask and add additional phosphoruscarrier solution t
35、o 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 factor of 2000 mustbe introduced
36、 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 calibration is specific for a give
37、ndetector 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 energy spectra as described in
38、 PracticeE 721 and Practice E 944.9.2235U 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 remains valid. Thereare sever
39、al 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 the shape of astandard p
40、ellet. 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. It is obtainedas a daught
41、er 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, e, for the detector system:e5Cftexp ltd# l tiN ssF 12exp2ltc#! 12exp2lti#!(1)where:C = counts rec
42、orded in detector, less background,ft= correction for coincidence losses, if needed,l =32P decay constant, = 5.625 3 107s1,td= decay time, s,tc= count time, s,ti= duration of irradiation, s,N = number of32S atoms in pellet,ss= spectrum-averaged cross section for32S in the calibra-tion neutron field,
43、 cm2=1024b, andF = 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 GuideE 1018.) The spectrum-averaged cross section for252Cf fissionneutrons is abou
44、t 70 mb, and for235U fission is about 63 mb.(See Table 2 and Refs (4-10).)10.1.2 The correction for coincidence losses, ft, 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 E 181). Coincidence loss correcti
45、ons can belarge, especially when Geiger-Mueller counters are used.NOTE 2Because of b 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 dimensions. The detection efficiencyshould be determine
46、d for each different pellet size that is to be used. Thevalue of N in Eq 1 can be taken to be the arithmetic mean over a numberTABLE 2 Neutron-induced Reactions in Sulfur Giving Radioactive ProductsReactionCross Section Cross Section (mb)ProductHalflife(1)MaximumEnergy ofProductBeta (MeV)(2)AverageE
47、nergy ofProductBeta(MeV) (2)IsotopicAbundanceofTarget (%)(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 3 1062.5 3 1052.572 s(13)5.3956(b +)1.9975(b +)95.02 (9)3.33S(n,
48、p)33P JENDL-3D3162 1.6 57.46 58.77 25.34 d(12)0.2485 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,a)31Si JENDL-3D3163 . 3.281 4.064 157.3 m(3)1.4908 0.59523 4.21 (8)6.34S(n,g)35S JENDL-3D3163 226 0.2749 0.2705 87.51 d(12)0.16684 0.04863 4.21 (8)7.3
49、6S(n,g)37S JENDL-3D3164 151 0.2511 0.2509 5.05 m(2)4.86516 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=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
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