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• METHOD 9310 • <br />1.0 SCOPE AND APPLICATION <br />GROSS ALPHA AND GROSS BETA <br />1.1 This method covers the measurement of gross alpha and gross bet <br />particle act~vit~es in surface and ground waters. <br />1.2 The method is applicable to the measurem ent of alpha emitters having <br />energi es above 3.9 mega electron volts (MeV) and beta emitters having maximu <br />energies above 0.1 MeV. <br />1.3 The minimum limit of concentration to which this method ~s applicabl <br />depends on sample size. counting-system characteristics, background. and countin <br />time. <br />1.4 Because. ~n this method for gross alpha and gross beta measurement <br />the radioactivity of the sample is not separated f rom the solids of the sample. <br />the solids concentration is very much a limiting factor ~n the sensitivity of th <br />method for any given water sample. Also. for samples with very to <br />concen trations of rad~oactiv~ty. it is essential to analyze as large a sampl <br />aliquot as is needed to give reasonable times. <br />a <br />m <br />e <br />9 <br />e <br />w <br />e <br />1.5 The largest sample aliquot that should be counted for gross alph a <br />activity ~s that size aliquot which gives a solids density thickness of 5 mg/cm Z <br />in the c ounting planchet. For a 2-in. diameter counting planchet (20 cm Z). a n <br />aliquot containing 100 mg of nitrated dissolved solids would be the maximu m <br />aliquot size for that sample which should be evaporated and counted for gros s <br />alpha activity. <br />1.6 When the concentration of total solids (TS) is known fora given Ovate r <br />sample and the alpha background and the counting e fficiency of a given counting <br />system are known. the counting time that is needed to meet the require d <br />sensitivity (3 pCi/L) can be determined by equations given in Appendix C. <br />1.7 For the counting of gross beta activity in a water sample. the TS is <br />not as 1 imiting as for gross alpha activity because beta particles are no t <br />stopped in solids as easily as are alpha particles Very often a single sample <br />aliquot is evaporated and counted for both gross a lpha and gross beta activity. <br />In that case, the sample aliquot size would be dictated by the solids limitation s <br />for alpha particles. For water samples that are to be counted far gross bet a <br />ac tivity. equations in Appendix C can also be used to determine the necessar y <br />counting time to meet a sensitivity for gross beta activity (4 pCi/L). <br />~--~- <br />1.8 Rad ionuclides that are volatile under the sample preparatio n <br />conditions of this method will not be measured. In some areas of the country <br />the nitrated water solids (sample evaporated with nitric acid present) wil 1 <br />9310 - 1 <br />CD-ROM Revision 0 <br />Date Seotember 1986 <br />