Re: Radon Screening

[David Biela <bielad@wv.doe.gov>]

>Date: 2-Oct-96 10:37:28 -0400
>From: RADSAFE@smtp (radsafe){radsafe@romulus.ehs.uiuc.edu}
>To: RADSAFE (Multiple recipients oflist){radsafe@romulus.ehs.uiuc.edu}
>Reply-to: RADSAFE@smtp{radsafe@romulus.ehs.uiuc.edu}
>Subject: Re: Radon Screening
>Message-id: AF9D523201CC2B79
>O-SMTP-Envelope-From: <radsafe@romulus.ehs.uiuc.edu>
>
>  From: Jeff Sawyer <74652.2361@CompuServe.COM>
>
>Franz, you wrote
>
>> a reading of 500dpm/100cm2 for alphas and ten
>time for betas seems to be rather high - especially for plate out of
>radon
>progeny.
>
>Most personnel contamination monitors try to cover as much body area as
>possible
>using arrays of large detectors. The problem with most large area
>detectors used
>in personnel contamination monitors is that they are typically larger
>(much)
>than 100 cm^2. The Eberline PCM-1C (commonly found in  power plants)
>uses
>detectors that are 500 cm^2. This means that you only need 100 dpm/cm^2
>to cause
>an alarm when the activity is uniformly distributed over the detector
>area.
>Newer instruments such as the PCM-2 refered to by Riasp use slightly
>smaller
>detectors (about 325 cm^2) which improves the situation a bit. Several
>instruments of this type also use sum zones which are designed to detect
>a 100
>cm^2 source positioned over two or more adjacent detectors. On the PCM-2
>this
>means that the area of the small sum zone is 650 cm^2 and even worse a
>sum zone
>of 4 detectors has an area of 1,300 cm^2 resulting in an alarm for 500
>dpm with
>only 38.5 dpm/100 cm^2 distributed.
>
>The problem is exacerbated (my only attempt at big words today) in
>facilities
>that use polyester coveralls which are a great collector of radon
>daughters. It
>is quite easy to get a uniform contamination from radon daughters on
>this type
>of clothing that will alarm a PCM from any manufacturer. There is a lot
>of
>experience at many power plants with people sitting on a bench waiting
>to decay
>before they can exit the monitors. I've even lost a pair of pants at
>Lasalle
>County Station due to radon and a tight flight schedule - but that's
>another
>story...
>
>The PCM-2 does have a novel radon compensation routine that looks at the
>ratio
>of alpha to beta and subtracts counts based on a signature. It has been
>found to
>be effective in power plants that are routinely monitoring for beta
>only.  The
>algorithm is not effective in situations with alphas and betas present
>in the
>contamination. (As I am sure everyone knows, radon daughter products are
>not
>"contamination" in the regulatory sense of the word.)
>
>Jeff Sawyer
>Eberline Instruments
>74652.2361@compuserve.com
>
Jeff,

5,000beta and 500 alpha are our sites gross alpha and beta numbers and are not based on radon.  
They are based on Sr and Pu.
Thanks
Dave