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Re: FW: Y-90
Now I'm puzzled. My response came from the 7th Table of Isotopes (Wiley-Interscience, 1978) and on page 352 the diagram pretty clearly shows Sr-90
decaying to the ground state of Y-90 with a 100% branching. Also on the following page it lists all the production routes for Y-90m, and Sr-90 decay
isn't among them. Also, we have done some work in our lab with Y-90 using fairly fresh samples (eluted on-site from Sr-90) and if the gammas from
Y-90m were significant, I'm sure we'd have seen 'em because were were trying to assay Y-90 samples in a gamma well counter (via bremsstrahlung). I
don't remember that we ever saw any discrete lines in the Y-90 spectrum using a NaI detector.
I don't have quick access to the later version of the Table of Isotopes so I can't say what's in it. Sounds like I'm either misreading the table
(very possible!) or something new was found and included in the compendium between 1978 and 1986 and we just missed the high energy lines. Or, Sr-90
really doesn't yield any Y-90m. Any ideas?
Joel
Jack_Earley@RL.GOV wrote:
> Forwarded w/ concurrence from David.
>
> Jack Earley
> Radiological Engineer
>
> -----Original Message-----
> From: David W Lee [mailto:lee_david_w@lanl.gov]
> Sent: Tuesday, February 12, 2002 1:36 PM
> To: Jack_Earley@RL.gov
> Subject: Y-90
>
> Jack:
>
> I believe both your nuc safety rep's and your own confusion can be solved
> by looking at page 90-1 and page 90-4 of Browne, Firestone, & Shirley Table
> of Isotopes (Wiley-Interscience 1986).
>
> Sr-90 (28.5 year half-life) is a pure beta emitter, but it beta decays
> 99.9979% of the time to Y-90m (3.19 hour half-life). This is the Yttrium
> that you correctly refer to below that has numerous gamma emissions. Its
> predominant gamma emissions are two gammas each about 15 keV (a total of
> 6+% of the time), a 202 keV (96.6% of the time), and a 480 keV gamma (91%
> of the time) with a 2.18 MeV gamma occurring 8.7 E-8% of the time and a
> 2.32 MeV gamma occurring 0.00173% of the time. A vanishingly small
> percentage of the time (1 - .999979), Sr-90 beta decays directly to Y-90
> (2.671 days half-life). This Y-90 has virtually no gamma emissions and
> beta emissions of 79 keV, 401 keV, and 432 keV. While your nuc safety rep
> was technically correct, I conclude that he/she did not realize that
> his/her favorite Y-90 results from Sr-90 decay such a vanishingly small
> percentage of the time. The Y-90m that you prefer is indeed the
> predominant result of the beta decay Sr-90. Most of the time, depending on
> the effective Z number of the container in which the Sr-Y-90 is stored, a
> large portion of any measured radiation field external to the source
> container is comprised of bremsstrahlung caused by the betas
> de-accelerating in the source encapsulation material. Best regards David
>
> At 12:19 PM 2/12/2002 -0800, you wrote:
> >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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>
> DAVID W. LEE, CHP
> Los Alamos National Laboratory
> Radiation Protection Services
> Radiological Engineering Team Leader
> ESH-12, MS K483
> Los Alamos, NM 87545
> PH: (505) 667-8085
> FAX: (505) 667-9726
> lee_david_w@lanl.gov
> ************************************************************************
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___________________________________________________________________________________
Any opinions expressed are exclusively my own and do not necessarily represent those of my employer.
Joel Lazewatsky, Ph.D. joel.lazewatsky@bms.com
Principal Research Scientist Tel: 978-671-8127; FAX: 978-667-3926
Bristol-Myers Squibb Medical Imaging
331 Treble Cove Road
N. Billerica, MA 01862
___________________________________________________________________________________
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