1、Designation:D308405(Reapproved 2012)Standard Practice forAlpha-Particle Spectrometry of Water1This standard is issued under the fixed designation D3084;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A numbe
2、r in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice covers the processes that are required toobtain well-resolved alpha-particle spectra from water samplesand discusses associated pr
3、oblems.This practice is generallycombined with specific chemical separations,mountingtechniques,and counting instrumentation,as referenced.1.2 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to es
4、tablish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2C859 Terminology Relating to Nuclear MaterialsC1163 Practice for Mounting Actinides for Alpha Spectrom-etry Using Neodymium FluorideD1129
5、 Terminology Relating to WaterD3648 Practices for the Measurement of RadioactivityD3865 Test Method for Plutonium in WaterD3972 Test Method for Isotopic Uranium in Water byRadiochemistry3.Terminology3.1 For definitions of terms used in this practice,refer toTerminologies D1129 and C859.For terms not
6、 found in theseterminologies,reference may be made to other publishedglossaries(1,2).34.Summary of Practice4.1 Alpha-particle spectrometry of radionuclides in water(also called alpha-particle pulse-height analysis)has beencarriedoutbyseveralmethodsinvolvingmagneticspectrometers,gas counters,scintill
7、ation spectrometers,nuclearemulsionplates,cloudchambers,absorptiontechniques,and solid-state counters.Gas counters,operatingeither as an ionization chamber or in the proportional region,have been widely used to identify and measure the relativeamounts of different-emitters.However,more recently,thes
8、olid-state counter has become the predominant system be-cause of its excellent resolution and compactness.Knoll(3)extensively discusses the characteristics of both detector types.4.2 Of the two gas-counting techniques,the pulsed ioniza-tion chamber is more widely used as it gives much betterresoluti
9、on than does the other.This is because there is nospread arising from multiplication or from imperfection of thewire such as occurs with the proportional counter.4.3 The semiconductor detectors used for alpha-particlespectrometry are similar in principle to ionization chambers.The ionization of the
10、gas by-particles gives rise to electron-ion pairs,while in a semiconductor detector,electron-holepairs are produced.Subsequently,the liberated changes arecollected by an electric field.In general,silicon detectors areused for alpha-particle spectrometry.These detectors are n-typebase material upon w
11、hich gold is evaporated or ions such asboron are implanted,making an electrical contact.A reversedbias is applied to the detector to reduce the leakage current andto create a depletion layer of free-charge carriers.This layer isthin and the leakage current is very low.Therefore,the slightinteraction
12、s of photons with the detector produce no signal.The effect of any interactions of beta particles with the detectorcan be eliminated by appropriate electronic discrimination(gating)of signals entering the multichannel analyzer.Asemiconductor detector detects all alpha particles emitted byradionuclid
13、es(approximately 2 to 10 MeV)with essentiallyequal efficiency,which simplifies its calibration.4.4 Semiconductor detectors have better resolution than gasdetectors because the average energy required to produce anelectron-hole pair in silicon is 3.5 6 0.1 eV(0.56 6 0.02 aJ)compared with from 25 to 3
14、0 eV(4.0 to 4.8 aJ)to produce anion pair in a gas ionization chamber.Detector resolution,defined as peak full-width at half-maximum height(FWHM),is customarily expressed in kiloelectron-volts.The FWHMincreases with increasing detector area,but is typically be-tween 15 and 60 keV.The background is no
15、rmally lower for a1This practice is under the jurisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.04 on Methods of RadiochemicalAnalysis.Current edition approved June 1,2012.Published August 2012.Originallyapproved in 1972.Last previous edition approved in
16、 2005 as D3084 05.DOI:10.1520/D3084-05R12.2For 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 boldface numbers in parentheses refer to the list of references at the end ofthis document.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 semiconductor dete
