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Y-90

I was "somewhat" surprised today to hear a nuc safety rep say that since

Sr-90 is pure beta, it doesn't need to be considered in a shielding

calculation. When I mentioned that it's in equilibrium w/ Y-90, which emits

some significant gammas, I was even more surprised to hear him say Y-90

doesn't emit gammas. Rather than address it further in the meeting, I pulled

up Grove's (Kocher) decay program, which showed only two betas for Y-90; no

gamma. But it then lists Y-90m w/ seven gammas ranging from about 2 keV to

0.7 MeV. My day for surprises, I guess--I've always associated Y-90 gammas

w/ 2+ MeV. Sure enough, my 15th edition of the chart shows 202 keV and 2.2

and 2.3 MeV gammas. So, since I'm apparently not the brightest bulb in the

lamp, can someone tell me why there's such a difference?



Jack Earley

Radiological Engineer

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