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Re: Tritium Smear Analysis




-----Ursprüngliche Nachricht-----
Von: Erik Nielsen <enielsen@antechltd.net>
An: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
Datum: Donnerstag, 18. Jänner 2001 22:10
Betreff: Re: Tritium Smear Analysis


>The method employed to analyze wipe samples for tritium depends on the
>chemical and physical form of the tritium.


It also depends on what your criteria for "removable contamination" are.
Radionuclides strongly bound to bricks surface will need other methods than
radionuclides in water soluble form on a working surface. Do you work with
strong mineral acids, organic solvents or water? I suggest that you use for
your smear samples the solvent (or probably no solvent), you are working
normally with. If it is tritiated water you are looking for, then a
moistened filter paper will do. (If you wait long enough the contamination
will go away anyway, probably contaminating your laboratory......)

Regarding the measurement conditions you should chose for the filter paper
(btw other materials for smear samples are available and should be chosen
according to your needs) you should check for suitable cocktails. If your
tritium is present as HTO and you use a filter paper moistened with water
you should chose a cocktail which can accomodate water. No additional
digestion is necessary, because white filter paper or similar material will
not exhibit any major quench effect. If you have oily smear samples, you
better use a cocktail for samples present in organic solutions.

One essential point is the determination of efficiency. I might sound old
fashioned, but I recommend that you use the method of the internal standard,
which means, that after measurement you add a known activity of tritium to
the LSC-vial and recount the vial. Whatever the influence of colour or
chemical quench might be - you will have the counting efficiency without the
need of establishing quench curves.

I remember a request for analysis about 20 years ago, when somebody
complained that his refrigerator had been contaminated, because some
RIA-sets with tritium had been stored in it for a few days. Tritium was
easily to be measured, but the conclusion of my investigation was simply,
that the tritium removable from 100 cm2 was equal to the amount of tritium
present in a cup of coffee made from water from the public water supply in
the early sixties.......

If further information is needed, please contact me at my private address.

Franz


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