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RE: Standards for the Taking
My own observation is that the efficiency for LSC units as measured using
old standards does not decline that I can detect. I did observe one
standard where the indicated efficiency of the C-14 standard dropped from
.97 to .75 or so. I called the manufacturer and the service engineer after
testing the LSC noted a slight discoloration of the label on the top of the
vial and concluded that fluid had seeped out through a crack in the flame
seal. A new standard fixed that problem. That standard by the way was <2
maybe even < 1 year old. They replaced the whole set, C-14, H-3 and
background free.
-----Original Message-----
From: Joel Baumbaugh [mailto:baumbaug@nosc.mil]
Sent: Wednesday, January 05, 2000 3:55 PM
To: Multiple recipients of list
Subject: RE: Standards for the Taking
Peter, Chris and Group,
I have been told by more than one manufacture that the L.S.
cocktail solution's fluors/phosphors/primary solutes (e.g. PPO [-
2,5-diphenyloxazole], PBD, p-terphenyl, BBOT, BPSB and dimethyl POPOP,
etc.) eventually deteriorate chemically due to the constant "bombardment"
from the radioactive sample, but "I" have not noticed any deterioration in
counts in older standards myself that were anything other than those you
mentioned below.
Joel Baumbaugh (baumbaug@nosc.mil)
SSC-SD
At 04:14 PM 01/05/2000 -0600, you wrote:
>Chris and Group,
>
>At one time I tried to establish just why or what the basis of 10 year
>expiration for sealed standards including but not limited to LSC standards.
>I got some responses, but all can be grouped under identifiable things that
>did not need a time limit. That is half life was given, but typically LSC
>standards are H-3 [12.25 y] and C-14 [5730 y] so by t-1/2 they can go for a
>while past 10 years. If statistics are bad for H-3, you can always count
>longer. I have noticed recently that newer LSC standards have 5 year
>expirations.
>
>That the basis might be an ANSI standard makes sense. But I am still
>wondering why the time limit?
>
>I have yet to get an explanation for the rational. I can testify that
>standards older than 10 years tend to deteriorate. Glue of for cap on top
>of flame sealed vial gets dry and may fail. Such a failure could cause a
>jam. But careful inspection should catch that. Labels deteriorate and
>such. But I am still interested in the rational or theoretical basis to
>retire a sealed standard, SOLELY ON AGE.
>
>Peter G. Vernig,
>
>As always my views are not necessarily those of the Dept. of Veterans
>Affairs, the Denver VA Medical Center or the US Government.
>
>Private replies may be directed to peter.vernig@med.va.gov
>
>-----Original Message-----
>From: Chris Alston [mailto:alstonc@odrge.odr.georgetown.edu]
>Sent: Wednesday, January 05, 2000 2:33 PM
>To: Multiple recipients of list
>Subject: Re: Standards for the Taking
>
>
>Isn't the ANSI "useful life" for LSC standards ten (10) years?
>
>cja
>alstonc@odrge.odr.georgetown.edu
>
>
> >1 Reference Background 3/1/83
> >
> >H-3 quenched standards
> ># Date DPM
> >1 3/1/83 91200
> >10 1/1/83 501000
> >6 1/5/74 502000
> >
> >C-14 quenched stds
> ># Date DPM
> >1 3/1/83 30200
> >6 12/5/73 208000
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