~~7009276O009877208DDesignation:D3085-75(Reapproved1983)StandardPracticeforMEASUREMENTOFLOW-LEVELACTIVITYINWATER’ThisstandardisissuedunderthefixeddesignationD3085:thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor.inthecaseofrevision.theyearoflastre\kion.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(0indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1Thispracticedescribestheprocessnec-essarytoobtainmeaningfuldatafromwatersamplesthatcontainlowlevels(cl0pCi)ofradioactivity.2.SummaryofPractice2.1Themeasurementoflowlevel(upto10pCi)fissionproductornaturalactivitiesinenvironmentalsamplesusuallyrequiressepa-rationoftheradioelementsoughtfromthewatersample.Normally,ameasurementofthegrossactivityofasampleisnon-specificand.therefore,oflittlevalue.Also,thesamplesizerequiredtodetectagivennuclidequantita-tivelymakesgrosscountingimpractical.Anadequateseparationofthenuclidesoughtfromthebulkmatrixcanusuallybeeffectedusingeithercamerorcarrier-freetechniques.2.2Itisconvenientalthoughnotabsolutelynecessarytoaddaradioactivetracertothesamplepriortothechemicalseparation.Thetracerisusuallyanotherisotopeoftheelementsoughtandonethathasadifferentmodeofdecay.Forexample,strontium-85,agammaemitter,iscommonlyusedtotracestrontium-90,abetaemitter.Thechemicalrecoveryofeachsamplemaythenbeeasilyandaccuratelydeterminedbygammacountingthefinalprod-uctoftheanalysisandcomparingthiscountwithaknownaliquotoftheoriginaltracersolution.2.3Ifthetracerinterfereswiththemeasure-mentofthenuclidesought,thenothermethodsfordeterminingrecoveryarenecessary.Oneverycommonmethodisthegravimetricrecov-eryofthecarrier.2.4Wheninvestigatinglowlevelsoffissionproductsornaturalactivitiesinenvironmentalsamples.contaminationofthesamplemayoc-curduetothepresenceofthenuclideofinterestinreagentsusedinsampleprocessing.Carefulanalysesofthesereagentsmustbeperformedtodeterminetheextentofthiscontamination.sothatitmaybesubtractedfromthefinalsamplevalue.Insomeinstances...
