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RE: Y-90
Thanks for everyone's input. I apparently received some bad training years
ago that I never felt the need to independently verify before this. I won't
say where it came from since their training program has been sufficiently
slammed over the years, although their training material was provided by a
contractor. Still a little confusion over one reference that may have
different data in editions that are 10 years apart--yet to be resolved.
Jack Earley
Radiological Engineer
-----Original Message-----
From: Dave Derenzo [mailto:dave@UIC.EDU]
Sent: Wednesday, February 13, 2002 5:56 AM
To: radsafe@list.vanderbilt.edu
Subject: RE: Y-90
Claude et. al,
Bremmstrahlung x rays are created in all absorbers, but the amount of
energy converted increases with atomic number of the absorber. The energy
of bremmstrahlung x rays is usually pretty low, usually under 100 keV. The
formula for estimating bremms hazard from a beta emitter is given in
Cember's book (3rd Ed.) as:
fraction of energy converted into photons = 1.5 x E(-4) Z E(max), i.e.,
0.00015 ZE(max).
For production with monoenergetic electrons, such as in an x-ray tube, the
formula is given as:
fraction = 1 x 100(-4) ZE. (that is 100 to the minus 4).
I would think the formula could be simplified to f = 0.01 ZE if I am
reading it correctly, someone pitch in if I am wrong.
Dave Derenzo, RSO
University of Illinois at Chicago
At 04:48 PM 2/12/02, Landes, Claude W wrote:
>Unless I' mistaken, Bremsstrahlung is only created when the Beta is
shielded
>or interacts with a high Z material such as lead. But Beta radiation is
>fairly easily shielded with aluminum or even paper, the exception being
high
>energy Beta's e.g. from Y-90. In this case a sheet of paper won't
completely
>shield them.
>
>In certain circumstances I have been able to indirectly confirm the
presence
>of Sr/Y-90 in a sample using Gamma Energy Analysis. I did this by taking
>into account a Bata dose rate from the sample and the absence of any lines
>in the Gamma spectrum save for a large amount of "low energy pileup". The
>low energy gammas in the spectrum are the Bremsstrahlung from the high
>energy Beta's interacting with the lead shield around my detector. Hey, I
>said it was indirect....
>
>Hope this didn't add too much confusion to the conversation.
>
>Claude W Landes, RRPT
>Senior Radiological Controls Technician, Lead
>ERC Radiological Counting Facility
>Eberline Services Hanford Inc.
>cwlandes@bhi-erc.com
>
>
>
>-----Original Message-----
>From: Franz Schoenhofer [mailto:franz.schoenhofer@CHELLO.AT]
>Sent: Tuesday, February 12, 2002 12:42 PM
>To: Jack_Earley@RL.GOV; radsafe@list.vanderbilt.edu
>Subject: Re: Y-90
>
>
>
>-----Ursprüngliche Nachricht-----
>Von: Jack_Earley@RL.GOV <Jack_Earley@RL.GOV>
>An: radsafe@list.vanderbilt.edu <radsafe@list.vanderbilt.edu>
>Datum: Dienstag, 12. Februar 2002 21:47
>Betreff: 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,
>
>I am not the brightest one in nuclear physics either (0.1 W), but I have
>worked as a radiochemist a lot with the analysis of Sr-90. Therefore I
think
>I can answer your question.
>
>First of all: yes, Sr-90 is a pure beta-emitter, therefore it cannot be
>measured by gamma-spectrometry like Cs-137, but needs time consuming and
>expensive chemical separation and special measurements methods - earlier
>Geiger- or proportional counters, nowadays liquid scintillation
spectrometry
>is the method of choice.
>
>Secondly: Y-90, the relatively short-lived daughter (about 64 hours), which
>therefore is very soon in equilibrium, is as well a pure beta-emitter, with
>relatively high beta - energy (about 2.3 Mev E-max). Y-90m is to my
>knowledge not part of the decay chain, Sr-90 decays directly to Y-90 (or
>maybe there is only a branch with an extremely low probability). Anyway
>there is no way to measure Sr-90 by gamma-spectrometry.
>
>Thirdly: To say, that you need not consider beta-emitters for shielding is
>surprising. You remember the story of the Sr-90 nuclear batteries in
Georgia
>recently? You cannot handle them with bare hands. Beta-particles have a
>certain range in air, if I remember correctly it is for a medium energy
>about 10 cm. So they have to be shielded. But when you shield them, there
>will be Bremsstrahlung created! And since this is electromagnetic
radiation
>it has to be shielded as well!
>
>I hope that some other one will shed more light with his 1000 W bulb on the
>problem of shielding beta radiation......
>
>Best regards,
>
>FRanz
>
>
>
>
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