Re: cesium-137 gamma abundance

[David Scherer <scherer@uiuc.edu>]

At 04:41 PM 10/22/96 -0500, you wrote:
>I have a question concerning the yield or abundance for the cesium-137 662
>keV gamma.  The lesson plans used here at Los Alamos National Laboratory
>(which are written by the DOE) use the 6CEN to get the exposure
>rate in R/hr, where C is the activity in curies, E is the energy of the
>gamma in MeV, and N is the percent abundance.  The lesson plan uses 85% as
>the abundance for the 662 keV gamma and I ahve ssen the 85% used elsewhere.
>When looking in books that show the decay scheme for cesium-137 they
>indicate that the abundance is 93.5%.
>
>Which one is correct?  Any thoughts on the subject would be appreciated.
>
Both.  Or neither.

Cs-137 decays to Ba-137m 94.6 percent of the time.  Ba-137m decays to Ba-137
ground state via gamma emission 89.98 percent of the time.  (The rest decay
via internal conversion.)  Thus, the overall yield for the 662 keV gamma is
85 percent (0.946 x 0.900).

Someone kindly pointed this out to me (via private mail) in response to a
mistake on a post some time ago.  The numbers above were taken from Kocher's
_Radioactive Decay Data Tables_  (DOE/TIC-11026, 1981).

Regards,
Dave Scherer
scherer@uiuc.edu