Gross Alpha is a gross measurement and used as a screening tool to determine whether more specific testing (i.e. expensive testing) is needed. There is no consideration for separation of multiple progeny as the question implies. Basically, if the gross alpha activity is less than 5 pCi/L, the gross alpha activity can be substitute for the Ra-226 activity. If the gross alpha activity exceeds 5 pCi/L, Ra-226 activity must be determined regardless of Ra-228 activity. EPA regulations do allow uranium activity to be subtracted for the gross alpha activity if it is present; subtraction of uranium activity leads to an adjusted gross alpha activity and as long as the adjusted gross alpha activity is less than 15 pCi/L, there is no gross alpha activity violation.
How do you subtract the levels of a particular alpha particle from the gross alpha results?
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