Re: Th-232 air sample analysis

[Christoph_Hofmeyr/CNS1@cns.co.za]

Radsafers,
I feel sympathy for anyone saddled with such a tough requirement, because
the potential for unwanted background would appear substantial if a
spectrometer is not used to discriminate.   I should, however, like to
point out that in later ICRP publications than 30 and 54 - e.g. 68, the
radio-toxicity of Th-232 (inhalation) has been downgraded by a factor of
effectively 30.  The ALI used to be 40 Bq/a equivalent to 50mSv (5 rem)
committed effective dose equivalent.  This changed to about 470 Bq/a
equivalent to 20 mSv (2 rem) committed effective dose.  Your limiting
Th-232 concentration translates to 1.5E-04 Bq/m^3, so that an adult living
in the exhaust stream would breathe in about 1.6 Bq/a and receive a
committed effective dose of about 7 mrem/a according to new data (also IAEA
International Basic Safety Standards, Safety Series No 115, Table II-III, 1
micron), or about 200 mrem/a according to  'old' data.  Quite a difference!
For your purposes there seems to be a legal requirement and the law is the
law, I guess.  My own thoughts.
Chris Hofmeyr
chofmeyr@cns.co.za

Original message:


Subject:  Th-232 air sample analysis




Radsafers,
Anyone have experience performing air sample analysis for Th-232?
We are investigating sampling methods for Th-232 which are sensitive
enough to meet the regulatory requirements for stack releases
(4E-15uCi/cc).  Is an alpha-spec system the only way to do this?

Thanks group!

Ed Stroud,  RRPT,  Alt.RSO
ed.stroud@state.co.us
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