Re:: Not getting what you paid for...

[baumbaug@nosc.mil (Joel T. Baumbaugh)]

     Scott,

     I'm  sorry  that I didn't go into more of an explanation  of
the  series of events leading up to this last vial.  I'll try and
be brief, yet cover the questions you and others raised.

     The purpose of the "original" order was incorporation of the
S-35   in  a  biological  experiment.   An  explanation  of   the
experiment  is  proprietary.  The uptake results,  however,  were
"way"  too  small  even when repeated.  This led to  the  vial(s)
activity being suspect.

     The  "vial"  in  question was the last of a  series  of  "4"
vials,  all  ordered  and  received  bearing  the   manufacture's
assurance  of  5 milicuries.  The vial in question, and  the  (3)
others  received  prior  to this event, have  been  counted  (and
recounted)  (using  a  Beckman  6000 series  LSC  which  has  98%
efficiency for unquenched
S-35)  to  ascertain  the amount of activity/milliliter  of  each
uncut  stock  vial's contents.  A check of all four vials  showed
the  same  result, i.e. 0.5 milicuries total activity - at  least
the  manufacture has been consistent (grin).  The samples HAVE to
be diluted as a microliter directly from the stock vial otherwise
"pegs out" the machine.

     As  a shortcut on the last vial's activity determination, it
was "automatically" cut by 1000/1 when received, and, as shown, I
came  up  with  the same activity/ul as was found  in  the  prior
vials.

     Scott,  if I truly had 5 mCi/172 ul of solution in my  stock
vial, and cut it 1000-1 would I not of had 1 million DPM/vial?

     BTW,  the experiment was carried out on 12 April, the vial's
reference date for 5 mCi was 15 April.

     Hope this helps,


     Joel

-----------------------------M/S-------------------------------

Date: Tue, 16 Apr 96 12:16:27 -0500
Sender: radsafe@romulus.ehs.uiuc.edu
From: "Scott O. Schwahn" <schwahn@CEBAF.GOV>
To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
Subject: Re: Not getting what you paid for...

At 10:58 AM 4/16/96 -0500, you wrote:
>     Group,
>
>      I  have  a  friend (not at my facility) who has   received
a
>number   of   vials  of S-35 from a vender (unnamed   for   now)
and
>believes   that   he is being "short changed" in the amount   he
is
>receiving.

No  - what you are really doing is making the assumption that  if
you do a 1000 to 1 dilution you will get 100,000 dpm/15 mL.  Your
math  just  showed you (correctly) that if you were to do such  a
dilution,  you  would  need to start out with about 0.5  mCi  per
vial.   Since you start out with 10X that much, you would have to
do  a 10,000 to 1 (approximately) dilution to get what you  want.
You  have to start with the manufacturer's decay-corrected figure
to come up with an appropriate dilution factor.

The   only   thing  that  should  make  you  believe   you   were
short-changed  is an actual measurement of the activity using the
LSC.

Scott O. Schwahn, CHP
Operational Health Physicist
Continuous Electron Beam Accelerator Facility
(804)249-7551 (w)
(804)249-7363 (fax)
schwahn@cebaf.gov