Re: Sealed sources

["J. J. Rozental" <josrozen@netmedia.net.il>]

At 06:43 PM 12/9/97 -0600, you wrote:
>Radsafers,
>
>At what time does a short lived sealed source cease being
>radioactive material.   Especially if the source has documenation
>identifying it as radioactive material and it was allowed to decay in
>storage.   If the source has decayed to undetectable levels can it
>then be disposed of as nonrad material.
>
>Stacey Alderson
>
=====================
Generally researchers work with radioactive substances, of order of mCi. For
such sources after 10 half-lives the source has decayed to order of  few uCi
or less. Since the great majority of these sources are only of moderate
radiotoxicity,  (group 3), or even low radiotoxicity, (group 4)  these
sourses can be disposed of  as non radioactive material. 
If the radioactive source is of order of 1-100 Ci, than 10 half lives, is
not enough to consider  the source non radioactive and  be disposed as non
radioactive material. Generally a source of 1-10 Ci of Ir-192 is considered
as spent source for industrial radiography user, and can't be disposed after
10 half-lives, or even 20 half-lives as non radioactive material. As a
matter of fact, there is not the activity the magnitude to consider a source
non radioactive, but the Specific Activity. Actually, many countries
consider nonradioactive,  the sources  of a Concentration of less than 100
Bq/g (~0.002 uCi/g for high radiotoxicity, (considering Ra-226 as
reference), this limit being increased to 500 Bq/g (~0.14 uCi/g) for solid
natural radioactive substances.

J. J. Rozental <josrozen@netmedia.net.il>
Israel