RE: High count with LSCh

["Ryder, R. (Roy)" <R.RYDER@dl.ac.uk>]

Ninni Jacob is of course correct when she says "that the high counts are
due to "Chemoluminescence", that is: "random single photon events which
are generated as a result of the chemical interaction of sample
components". It is due to the presence of certain chemicals in the
sample. Yes, the counts do go down with time.
It also helps to "dark adapt" the samples." The excess counts are often
caused by the impurities of generated by use in the pump, although some
brands of new oil will also exhibit this effect. We have tried slowing
down the reaction kinematics by cooling the sample with limited success.
A far better solution was to speed up the reaction kinematics by heating
the sample (in the scintillator) to around 50 deg centigrade for a few
hours. An hour in the dark before counting should give a more or less
constant count with time. It may be necessary to experiment to get the
best conditions.

Roy Ryder

Daresbury Laboratory, UK



> ----------
> From: 	HALEEM  MAHMOUD SAID[SMTP:mshaleem@dpc.kfupm.edu.sa]
> Reply To: 	radsafe@romulus.ehs.uiuc.edu
> Sent: 	 16 March 1998 8:46 PM
> To: 	Multiple recipients of list
> Subject: 	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
>