Re: Th-232 air sample analysis

["Paul R. Steinmeyer" <prstein@gyral.com>]

We meet this limit using a dedicated zinc sulfide alpha scintillator (Ludlum
43-1) attached to a scaler (Ludlum Model 1000).  The air sample needs to be
fairly high volume, though.  Using the following parameters gives an LLD of
3.8E-15 µCi/mL

    blank count rate = 4 cpm or less
    counting time (of blank and sample) = 5760 minutes (i.e., 4 days) or
greater
    sample volume = 7E7 mL or greater
    detector effeiciency = 0.23 c/d or greater
    filter efficiency = 0.9997
    filter fraction = 1 (the whole thing fits under the detector)
    self-absorption factor for alpha/glass fiber filter = 0.9

Obviously, there's some difficulty with this method if you need a high
sample throughput rate...

If you'd like additional information, don't hesitate to contact me.

Paul R. Steinmeyer
Radiation Safety Associates, Inc.
RSA Laboratories, Inc.
mailto:prstein@radpro.com

Ed Stroud wrote:

> 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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