AW: [ RadSafe ] Medium for gas geometry calibration

[Franz Schönhofer]

Hej,

I wonder, what kind of gas you want to measure. Since you obviously work at
Forsmark I would have thought that gaseous activities from a nuclear power
plant would be mostly noble gases and iodine. Usually these gases are
adsorbed in a bypass on charcoal and then this charcoal is measured. The
uneven distribution of the radionuclides in the cartridge is another problem
concerning the geometry. I remember that there was a solution by measuring
two times, turning the cartridge upside down for the repeat and probably
some other tricks, including calculations, which I do not remember in
detail.

>From my frequent work to produce gamma-spectrometric standards I remember
that I used a resin, produced by mixing two liquid components together, one
previously mixed with the standard. Fortunately I was aware of the pH of the
standard solution and made inactive tests. They showed, that the resin would
never polymerize under these pH conditions. It was a terribly time consuming
work to find out suitable neutralization conditions and mixing ratios. After
all it was clear that production in this way was far more expensive than
ordering custom made ones from Analytics Inc. - which we did in the future.
I wonder, whether these resins would not be also representative for gases.
At the worst you would probably have to make small corrections for the
almost negligible absorption by the resin.

For our calibration standards with different materials of much different
matrices I used ion exchange resins. I adsorbed small amounts of the
standard on a not to small amount (maybe tens of grams) of ion exchange
beads and after drying those beads were mixed using a 3-dimensional tumbler
with a large amount of the matrix material (usually about a liter). This
worked well. 

Finally a provocative question: What could the difference due to matrix
effects be between water and gas?

Hur star det till i Forsmark efter den stora skandalen?????

Med vaenlig haelsning

Franz

Franz Schoenhofer, PhD
MinRat i.R.
Habicherg. 31/7
A-1160 Wien/Vienna
AUSTRIA


-----Ursprüngliche Nachricht-----
Von: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] Im Auftrag
von Olsson Mattias :MSO
Gesendet: Dienstag, 11. September 2007 09:06
An: radsafe at radlab.nl
Betreff: [ RadSafe ] Medium for gas geometry calibration

Hello,

I ended up calibrating the efficiency of a HPGe detector system the other
month. It was done from a simple mixed gamma ampoule that was diluted in the
old fashioned way. There were several geometries och which some were for gas
samples (such as gas in a Marinelli beaker). Of course, a professionally
made source with a foamed plastic medium or such could have been used, but
did I? No. Budget etc. There was an old instruction that suggested that the
medium that should be used to suspend the activity was a regular ion
exchange resin. It seemed like a rather rough replacement for gas to me.

Does any radsafers have experience with home made gas geometries, and what
did you use for a medium? (The use of an actual gas or Labsocs are not
options in this case).

Take care!

Mattias Olsson

-- 
Mattias Olsson, FTKS
Forsmarks Kraftgrupp AB
742 03 Östhammar

t. 0173-81952
m. 0705-801952
e. mso at forsmark.vattenfall.se
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