RE: High count with LSCh

["Campbell John CP USGR EXC" <john.campbell@cp.Novartis.com>]

 This is a common problem when counting oils or other highly quenched samples.
 The problem is photoluminescence.  The solution is to chill the sample or 
store in darkness for some time.
John Nash Campbell

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 Schoenhofer
 Habichergasse 31/7
 A-1160 Wien
 AUSTRIA
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 Mobiltel.: +43-664-3380333
 e-mail: schoenho@via.at
 -----Urspr=FCngliche Nachricht-----
 Von: HALEEM MAHMOUD SAID <mshaleem@dpc.kfupm.edu.sa>
 An: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
 Datum: Montag, 16. M=E4rz 1998 21:47
 Betreff: High count with LSCh


 >Hello safety netters
 >
 >I have this question regarding high count rate with the liquid
 >scintillation counter.  Whenever a sample of oil vacuum pump of
 >anccelerator is counted I get high count rate with initial count.
 >However, when the sample is counted again latter on, the response is
 >numerical value, and the value keep decreasing when counted repeatedly
 >over time until stalbilizes latter on like 24 hours latter.  The same
 >thing occurred when counting saliva samples.  I was wondering if any of
 >you could give an explanation for this situation either from past
 >experience or an educated guess.  Your help is very much appreciated.
 >Thanks.
 >
 >
 >Mahmoud Haleem
 >KFUPM
 >P.O.Box 1061
 >Dhahran 31261
 >Saudi Arabia
 >mshaleem@dpc.kfupm.edu.sa
 >------------------------------------------------------------------------=
 ---
 -----------------------

 Dear Mr. Mahmoud,

 Thanks for your contribution, which confirms an observation I made about =
 a
 year ago. I remember very well that we had a smear sample from the vicini=
 ty
 of a Fe-55 source. Since the area from which the smear sample was taken w=
 as
 lubricated, the smear sample contained some mineral oil. We also saw with
 our Quantulus counters chemiluminescence (this counter offers the
 possibility of measuring chemiluminescence independently of the sample). =
 It
 took several days to decay. We had no time to go further into details, bu=
 t
 it would be worthwhile to do it now. Do you have any further observation,
 for instance what another RADSAFER suggested, to measure the original
 mineral oil? Please contact me for further exchange at my personal e-mail
 address.

 In my opinion measurement of low beta-energy emitters is a very interesti=
 ng
 and useful application of liquid scintillation measurements. However in s=
 ome
 cases chemiluminescence might interfere.

 Regards,

 Franz