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Re: U.S. NRC proposes changes to shallow dose exposure limit
The reason I asked this question:
1) The concern of Mo, SS and W filtered x-ray
diffration unit primary beams, where the affected area
may only be 1 cm2 or less.
2) An exposure of a focused electron beam,
from a machine or a radioactive source where the
affected area may be only 1 cm2 or less.
It seems to me that the effective shallow tissue dose
equivalent limit for these would be 0.5 Sv per year
irrespective of beam diameter at the point of
exposure. Perhaps I am wrong here. These are not
covered by 10 CFR 20 for the most part, but by state
regulations
3) Consistency with the MPE(skin) for lasers
which have wavelengths in the range of about 180 nm to
400 nm, which are equivalent to ~ 0.006 to 1 Jcm-2,
where the affected area may be 1 cm2.
What ever happened to the "proposal" which
stated "exposure to the skin from a point source or
particle of unknown size but less than 1 mm in
diameter is limited to 10 billion beta particles
emitted from the radionuclides contained in the
particle. For the case of 1 beta per disintegration,
the limit is expressed as 10 Gbq or 75 uCi h?
Was this too conservative or too hard to work with?
Paul Shafer
--- Mike Lantz <mlantz33@cybertrails.com> wrote:
> This is for hot particles on and off the skin. It
> was designed for that
> source: hot particles.
>
> Mike
>
> Paul William Shafer wrote:
>
> > Am I correct in saying that "the effective shallow
> > dose equivalent (Hs) is the exposure of the skin
> or an
> > extremity from external sources of ionizing
> radiation
> > at a tissue depth of 7 mg/cm2 averaged over 1
> cm2?"
> >
> > Isn't this definition designed for radiation
> exposure
> > from sources which are external to (not in contact
> > with) the affected tissue?
> >
> > Paul Shafer
> > --- Mike Lantz <mlantz33@CYBERTRAILS.COM> wrote:
> > > I think some of you know that I was on the NCRP
> > > committee that came up with the
> > > 10 cm2 limit. I'm very happy with this value
> for
> > > hot particles as a limit for
> > > deterministic effects - especially as it is a
> > > unified limit of 50 rem for skin.
> > > There is far too much to talk about over
> Radsafe, so
> > > if you want to talk about
> > > how we came to 10 cm2 and its value, call me at
> 623
> > > 393 5200. As an example, 1
> > > cm2 was never a biological endpoint from hot
> > > particles - it was equally
> > > arbitrary as most effects studied on pig
> > > irradiations were 1-2 mm2 from the
> > > betas. However, many particles are stepped on
> and
> > > attached to shoes - one
> > > station just encountered this problem. And
> these
> > > particles expose larger areas
> > > than 1 cm2 from the photons.
> > >
> > > We discussed and wrote about the stochastic
> effects
> > > from hot particles and
> > > determined them to be negligible, of course.
> > >
> > > Mike Lantz, CHP
> > >
> > > glen.vickers@EXELONCORP.COM wrote:
> > >
> > > > 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
> > > > >
> > > > > Costa Mesa, CA 92626
> > > > >
> > > > > Personal Website:
> > > http://www.geocities.com/scperle
> > > > > ICN Worldwide Dosimetry Website:
> > > http://www.dosimetry.com
> > > > >
> > > > >
> > >
> >
>
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