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Tracy:
What sealed sources have short enough half-lives to be decayed
in storage? Only I-125 seeds come to mind at the moment. But, even so, the DIS
paradigm is generally held only to be applicable to "waste", that is
contaminated gloves, glassware, empty stock vials, etc. The idea is that the
activity you start out with is very small so that it will reach background after
ten half-lives or so. If you start out with a 10 millicurie source, say,
after ten half-lives you've still got 10 microcuries, which (hopefully) will be
far above your background.
Your regulator may have objections to placing sources into
DIS. I would.
There has been one notable exception, that being spent moly
generators. These are not sealed sources, but the initial activity is very high.
They had been considered appropriate for DIS because the half-life is so short.
BUT, we are finding that due to long lived contaminants, at least from some
manufacturers, the spent columns never get down to background! When
DIS becomes indefinite storage its no longer appropriate.
************************************************************************ Clayton Bradt, CHP <raldrich@nysnet.net> phone: 518/457-1202 Assoc. Radiophysicist fax: 518/485-7406 NYS Dept. of Labor Radiological Health Unit Blg.12, Rm 169 State Office Campus Albany, NY 12240 *********************************************************************** |