Re: Sealed sources

[Rrk099 <Rrk099@aol.com>]

Greetings from one of those (former) regulator types -

Decay in storage (DIS) is not defined in New York City's regulations (nor, I
believe, in 10 CFR), but may be in those of other Agreement States.  If you
are subject to an AS jurisdiction, you must comply with its regulations.

In general, as a regulator, the rule of thumb is DIS for 10 half-lives AND
measurement with an appropriate survey meter in a low background area to
ensure the source is indistinguishable from background.  This does not ensure
the source is "non-radioactive," but allows the source to be disposed as if it
were not radioactive.  As has been previously pointed out in this thread, the
initial activity of the source is important since 10 half-lives yields a
reduction in activity to approximately 0.001 of the original.

The specific conditions under which a licensee operates for DIS is usually
part of the license application and approval.

Hope this helps.

Bob Kulikowski