Re: LSC for Gross Alpha Counting

[Schoenhofer <schoenho@via.at>]

At 02:24 18.02.1997 -0600, you wrote:
>Hi everyone
>
>We are about to replace our 15-year-old Beckman LS Counter, probably 
>with a new Beckman or Packard unit.
>
>While we need to replace it just for tritium analyses, we are hoping 
>to be able to perform gross alpha analyses as well, which would 
>provide a backup for our gas-proportional counter.
>
>Our samples (nuclear power plant) typically contain very high beta 
>activity but negligible alpha activity.  One can configure a 
>gas-proportional counter such that the beta crosstalk is practically 
>non-existent (<0.001%) in order to achieve acceptable alpha detection 
>limits.
>
>What I would like to know is, can the beta crosstalk on modern LS 
>counters be reduced to that sort of level.  ANY false positive alphas 
>at all would be a problem for us.
>
>Any advice would be greatly appreciated.
>
>Andrew
>
>
>Andrew Welsh
>Chemistry Development Section
>Koeberg Nuclear Power Station
>Private Bag X10
>KERNKRAG 7440
>South Africa
>Tel: +27 (0)21 5504298
>Fax: +27 (0)21 5505117
>E-mail: welsha@kbpnfs01.eskom.co.za
>
>.....................................................................

Andrew,

We use four LS counters of the type "Quantulus" from the company Wallac OY,
Turku, Finland. They are equipped with alpha-beta-discrimination units,
which very effectively can discriminate alpha and beta particles. We use the
discrimination to reduce the beta background (and the normal background) to
practically zero in our work for radium-226 determination. You do not
specify the isotopes you expect and the beta emitters which are present. If
it is only tritium, then you would not even need any separation, because due
to the extremely low maximum energy of tritium and the high energy of the
alphas there would be no overspill. (Alpha particles show up in the pulse
height spectrum in the energy range of about 400 keV betas.) The
alpha-beta-separation is highly dependend on the energy of both alphas and
betas, of the cocktail used, quench etc. It can be adjusted anyway to reduce
cross talk from beta to alpha to zero, though a little efficiency for the
alphas may be lost.

This is what I can tell you now, for more one would need to know the systems
you use. I would also recommend to contact Dr. Lauri Kaihola from Wallac at
lkai@mail.wallac.fi, who sure is able to give you more information on that
topic.

Franz
Schoenhofer
Habichergasse 31/7
A-1160 WIEN
AUSTRIA/EUROPE
Tel./Fax:	+43-1-4955308
Tel.:		+43-664-3380333
e-mail:		schoenho@via.at