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RE: U.S. NRC proposes changes to shallow dose exposure limit
I've been away from skin dose for a couple of years, but here are a couple
issues I can think of right away.
I believe the organ weighting factors assume uniform irradiation of the
entire organ and that will essentially never be the case for skin
contamination events.
If they're thinking about changing the rules, then they need to also think
about practical ways to calculate the quantities. Right now, if a person
had varying levels of contamination on a planar source, the tech would take
the highest direct reading with a 15.5 cm^2 GM probe and we'd calculate that
as a 15.5 cm^2 source over a 1cm^2 receptor. Some might concentrate that
reading as a 1 cm^2 source over a 1 cm^2 receptor, but that bumps up the SDE
by about a factor of 15 for Co-60. I'd like to see some additional guidance
about assumptions of the source size, because you can't really measure, and
activity/probe area. With the new guidance should we take the reading/15.5
cm^2 and apply that activity/cm^2 as a 10 cm^2 source over a 10 cm^2
receptor? Different approaches yield signficantly different answers.
Why change to 10 cm? The calculated doses will drop significantly. Why not
just increase the limit over the same 1 cm^2 if we think we are overstating
the stochastic risks from planar sources?
What about deterministic effects from hot particles? The NRC's enforcement
guidance stated that a limit of 75 uCi-hr would be applied in addition to
the 50 rem SDE. NRC (IE 90-48, NCRP 106) Also hot particle dose is not
SDE, but SD or hot particle dose. The NRC needs to codify gudiance for
point and planar sources. They did a good job with the enforcement
guidance, but now would be the time to address the issue appropriately.
Glen Vickers
> -----Original Message-----
> From: Sandy Perle [SMTP:sandyfl@EARTHLINK.NET]
> Sent: Thursday, July 12, 2001 9:58 AM
> To: radsafe@list.vanderbilt.edu
> Subject: Re: U.S. NRC proposes changes to shallow dose exposure limit
>
> > This is in keeping with the recommendations found in NCRP 130.
>
> While this proposal is an improvement, the NRC needs to move towards
> acceptance of dose weighting. The skin, being an organ, should be
> viewed as other organs are, and where there are weighting factor
> applied, if the NRC would accept the methodology, such as what is
> outlined in HPS N13.41-1997.
>
> In my opinion, it is still unrealistic and not logical to assign a
> SDE based on the highest 1 cm, 10 cm or whatever number of cm's one
> wants to consider, when in all practicality, the cumulative dose
> effect to the person is insignificant. Now, for very high dose
> particles, I can agree that averaging needs to be assessed. However,
> for the general population of workers, using the highest dose nees to
> be re-thought.
>
> ------------------------------------------------------------------------
> Sandy Perle Tel:(714) 545-0100 / (800)
> 548-5100
> Director, Technical Extension 2306
>
> ICN Worldwide Dosimetry Service Fax:(714) 668-3149
>
> ICN Pharmaceuticals, Inc. E-Mail:
> sandyfl@earthlink.net
>
> ICN Plaza, 3300 Hyland Avenue E-Mail: sperle@icnpharm.com
>
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>
> Personal Website: http://www.geocities.com/scperle
> ICN Worldwide Dosimetry Website: http://www.dosimetry.com
>
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