[ RadSafe ] Looking for References on Liquid Counting for Tritium

[Kaihola, Lauri]

Hello Felipe,

1. Acetone introduces much quench, but Tritium signal is well measurable
though.  Acetone quenching was discussed by S.W. Wunderly, Evaluation of
liquid scintillation counting accuracy: effect of various chemical quenching
agents and effect of milky sample preparations, in Advances in Scintillation
Counting", eds. S.A. McQuarrie, C. Ediss and L.I. Wiebe, Banff, University
of Alberta Press 1983, pp.  376-393.  The same matter was considered when
Wallac developed spectrum library concept for LSCs:  Kenneth Rundt, The
effect of quench curve shape of the solvent and quencher in a liquid
scintillation counter,  in Ross, H.,  Noakes, J.E. and Spaulding, J.D.,
eds., Liquid Scintillation Counting and Organic Scintillators, Lewis
Publishers, 1991, pp. 257-268.

2. It is possible to monitor random coincidence signal in an LSC.  Quantulus
contains a delayed coincidence circuitry operating simultaneously with
prompt coincidence circuitry and enabling storage of pure random coincidence
and sample spectra.  The (stable) random coincidence signal from phototube
thermal noise is about 0.20 CPM.  Any (chemi)luminescence signal would not
be stable and is also easily recognizable by its shape and location in low
channels.  Strong sonoluminescence signal will be present during acoustic
cavitation, but should disappear when acoustic excitation is terminated.

3. Tritium detection by LSC should be fine, when it can be done off-line.

Sincerely,

Lauri

Lauri Kaihola, Ph.D.
Associate Product Leader
PerkinElmer Life and Analytical Sciences
Wallac Oy
P.O. Box 10
FIN-20101 Turku
Finland
 
Tel.       +358 2 267 8376
Mobile +358 40 847 5697
Fax       +358 2 267 8332,   +358 2 267 8357
 
Email:   lauri.kaihola at perkinelmer.com
http://www.perkinelmer.com

Message: 11
Date: Tue, 6 Sep 2005 12:26:45 -0700
From: Felipe Gaitan <gaitan at impulsedevices.com>
Subject: RE: [ RadSafe ] Looking for References on Liquid
	Scintillation	Counting for Tritium
To: radsafe at radlab.nl
Message-ID: <p06110413bf439d53350e@[192.168.1.119]>
Content-Type: text/plain; charset="us-ascii" ; format="flowed"

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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