ASTM_E_2426_-_10.pdf

Designation:E242610Standard Practice forPulse Counting System Dead Time Determination byMeasuring Isotopic Ratios with SIMS1This standard is issued under the fixed designation E2426;the number immediately following the designation indicates the year oforiginal adoption or,in the 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.1.Scope1.1 This practice provides the Secondary Ion Mass Spec-trometry(SIMS)analyst with a method for determining thedead time of the pulse-counting detection systems on theinstrument.This practice also allows the analyst to determinewhether the apparent dead time is independent of count rate.1.2 This practice is applicable to most types of massspectrometers that have pulse-counting detectors.1.3 This practice does not describe methods for precise oraccurate isotopic ratio measurements.1.4 This practice does not describe methods for the properoperation of pulse counting systems and detectors for massspectrometry.1.5 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 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2E673 Terminology Relating to Surface Analysis(Withdrawn2012)32.2 ISO Standards:4ISO 21270 Surface Chemical AnalysisX-ray photoelec-tron and Auger electron spectrometersLinearity of in-tensity scale;and references 1,2,10,13 and 14 therein.3.Terminology3.1 Definitions:3.1.1 See Terminology E673 for definitions of terms used inSIMS.3.1.2 See Terminology ISO 21270 for definitions of termsrelated to counting system measurements.3.1.3 isotopic ratio,nwritten asm2X/m1X,for an elementX with isotopes m1 and m2,refers to the ratios of their atomicabundances.When it is a value measured in a mass spectrom-eter it refers to the ratio of the signal intensities for the twospecies.3.1.3.1 DiscussionThe notation m2X or m2X refers to thefractional deviation of the measured isotopic ratio from thestandard ratio or reference.In this practice,m2X will refer tothe fractional deviation of the measured ratio,uncorrected formass-fractionation(see 3.1.4)and m2X will refer to thefractional deviation of the measured ratio that has beencorrected for mass-fractionation.An example for magnesium(Mg)is:25Mg525Mg/24Mg!Meas25Mg/24Mg!Ref2 1(1)where:(25Mg/24Mg)Ref=0.126635.3.1.4 mass-fractionation,nsometimes called“mass-bias,”refers to the total mass-dependent,intra-isotope variation in ionintensity observed in the measured isotopic ratios for a givenelement compared with the reference ratios.It can be expressedas the fractional deviation per unit mass.3.1.4.1 DiscussionThe mass of an isotope i of element X(miX)shall be represented by the notation mi,where“i”is aninteger.4.Summary of Practice4.1 This practice describes a method whereby the overalleffective dead time of a pulse counting system can be deter-mined by measuring isotopic ratios of an element having atleast 3 isotopes.One of the isotopes should be approximately1This practice is under the jurisdiction of ASTM Committee E42 on SurfaceAnalysis and is the direct responsibility of Subcommittee E42.06 on SIMS.Current edition approved June 1,2010.Published July 2010.Originally approvedin 2005.last previous edition approved in 2006 as E2426 05(2006).DOI:10.1520/E2426-10.2For 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 last approved version of this historical standard is referenced onwww.astm.org.4Available from International Organization for Standardization(ISO),1,ch.dela Voie-Creuse,Case postale 56,CH-1211,Geneva 20,Switzerland,http:/www.iso.ch.5Catanzaro,E.J.,Murphy T.J.,Garner E.L.,and Shields W.R.,“AbsoluteIsotopicAbundance Ratios andAtomic Weight of Magnesium,”Journal of Researchof the National Bureau of Standards,Vol 70a,1966,pp.453458.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 a factor of 10 more abundant than the others so that a first orderestimate of the dead time can be calculated that will be close tothe true value.The efficacy of the method is increased if thesample is flat and uniform,such as a silver(Si)wafer or apolished metal block so that the count rate of the isotopesvaries minimally during the individual measurements.5.Significance and Use5.1 Electron multipliers are commonly used in pulse-counting mode to detect ions from magnetic sector massspectrometers.The electronics used to amplify,detect andcount pulses from the electron multipliers always have acharacteristic time interval after the detection of a pulse,duringwhich no o