[ RadSafe ] RE: Looking for References on Liquid Scintillation Counting for Tritium

Wed Sep 7 02:15:29 CDT 2005

Felipe,

In general there are several ways to reduce the influence of 
(Chemo)Lumenescence (CL). The most used ones are:

- Usage of a special LSC-cocktail that is less sensitive for CL.
- Adjusting (usually reducing) the pH of the countingsample.
- Preparing the samples out of direct (sun)light.
- Apply a waiting time between the preparation and counting of the 
samples (eg. 24 h).
- Counting the samples two or three-times with some time in between. 
Since CL will reduce in time this will give some idea about the 
contributuion of CL to the countrate.

CL can be distinguished by most modern LCS-counters since the photons 
produced in so-called single events. The photons can be quite easily 
distinguished from beta-pulses by the coincidence circuit. Because of 
this be sure your LSC-counter has coincidence-counting turned on and 
single photon-count turned off. On most counters this is default. On 
many modern counters there is a feature called lumenescence correction. 
Check your manual for this option.

Hope this helps some. Feel free to contact me if you have any further 
questions.

With kind regards,

Marcel Schouwenburg - RadSafe moderator & List owner
Head Training Centre Delft
National Centre for Radiation Protection (Dutch abbr. NCSV)

Faculty of Applied Sciences / Reactor Institute Delft
Delft University of Technology
Mekelweg 15
NL - 2629 JB  DELFT
The Netherlands
Phone +31 (0)15 27 86575
Fax     +31 (0)15 27 81717
email   m.schouwenburg at tnw.tudelft.nl

Dimiter Popoff wrote:

> Felipe,
>
>  
>
>> 2.  Are there techniques for eliminating CL interference at low count
>> rates (a few CPM above background)?
>>    
>>
>
>Since they all use photomultiplyer tubes, your only bet would be some sort
>of light intensity based discrimination, if the difference is present in the
>signal. I don't know whether commercial lsc devices do this (I am sure Franz can
>shed more light on that), but it is no rocket science to do, should be
>doable one way or the other.
> However, I would think twice if not more about the actual availability of
>a signal to go after (i.e. whether there is _some_ difference between
>the light pulses because of the causing phenomeon), I have no clue here.
>
>Dimiter
>
>
>------------------------------------------------------
>Dimiter Popoff               Transgalactic Instruments
>
>http://www.tgi-sci.com
>------------------------------------------------------
>
>
>-------Original Message-------
>  
>
>>From: Felipe Gaitan <gaitan at impulsedevices.com>
>>Subject: RE: [ RadSafe ] Looking for References on Liquid Scintillation	Counting for Tritium
>>Sent: Sep 06 '05 22:26
>>
>> Gentlemen,
>> 
>> Thank you Alex, Franz and Bob for your response.  I'm writing to the
>> list in case other people are interested but we could communicate off
>> line if you prefer.
>> 
>> So far the consensus is that there are no definite references due to
>> the fast pace of development and that the two main categories are
>> high and low count rates.  So it looks like I need to give more
>> details about our particular application.
>> 
>> We are trying to replicate an experiment done at Oak Ridge (and more
>> recently at Purdue) in which the authors claim to be producing
>> Tritium in deuterated acetone using acoustic cavitation.
>> 
>> Here is a summary of what I consider are the relevant parameters (let
>> me know if you think I'm missing any):
>> 
>> 1.  Sample liquid:  both regular and deuterated acetone.  According
>> to the authors, the tritium backgrounds for regular and deuterated
>> acetone are about 20 CPM and 50 CPM respectively. Deuterated acetone
>> has a higher background due to tritium contamination (I assume during
>> the deuteration process).  As far as I know, they have used regular
>> (not super-low background) LS counters (Beckman LS6500, I believe)
>> 
>> 2.  They measure anywhere between 2-15 CPM above background for the
>> deuterated acetone (none for the other control samples including
>> regular acetone)
>> 
>> 3.  I'm aware that chemiluminescence (CL) and other types of
>> luminescence can interfere with tritium measurements and I don't know
>> if or how the authors compensated for it. I wouldn't be surprised if
>> acoustic irradiation could excite some molecules and cause them to
>> emit photons. I don't think the regular machines can compensate for
>> CL when the count rate is that low (right?).  The only way I know is
>> to monitor the count rate (both coincident and non-coincident) as a
>> function of time.
>> 
>> Here are my questions:
>> 
>> 1.  Do you know anybody measuring low levels of tritium is acetone
>> samples? I'm wondering if there are particular issues with acetone.
>> 
>> 2.  Are there techniques for eliminating CL interference at low count
>> rates (a few CPM above background)?
>> 
>> 3.  What other effects can interfere with this kind of measurements?
>> 
>> Thanks in advance,
>> 
>> Felipe
>> 
>> --
>> D. Felipe Gaitan, Ph.D.
>> Chief Scientific Officer
>> Impulse Devices, Inc.
>> 13366 Grass Valley Av.  Unit H
>> Grass Valley, CA  95945
>> Phone: 530-273-6500 Ext. 112
>> Fax:  806-498-6731
>> 
>> email: gaitan at impulsedevices.com
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>>    
>>
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