RE: S.Korea Launches Probe Into Nuclear Accident

["Heinmiller, Bruce" <heinmillerb@aecl.ca>]

Correct!  See my 10:40 Oct 1 posting.

A quoted dose of, say, 10 Sv is ambiguous, because no quantity is specified.
If it was derived from biological dosimetry and represents the estimated
corresponding low-LET dose (10 Gy or 10 Sv) that would have caused the
observed effects noted, then the prognosis is poor.  On the other hand, if
it represents the true (but inappropriately used) dose equivalent, and
supposing equal absorbed doses from neutrons and photons (a plausible
scenario), then the absorbed dose of each would be slightly under 1 Gy if a
quality factor of 10 had been applied to the neutron absorbed dose.  If
neutrons are 2 to 3 times as effective for producing the acute effects of
concern, then it would look to the body like a total low-LET dose of about 3
Gy, and the prognosis would be much better.

Also, here's what ICRU, ICRP, and IAEA have to say about the use of dose
equivalent quantities for high-dose exposures, particular where neutrons are
involved.  I've extracted this from an off-list question that I replied to
earlier.

For example, ICRU Report 51 states that the quality factor "is formulated to
take account of the relative effectiveness of the different types of
ionizing radiations at the low exposure levels encountered in routine
radiation protection practice."

And ICRP, in Publication 60, states:  "The equivalent dose is not always the
appropriate quantity for use in relation to deterministic effects because
the values of radiation weighting factors have been chosen to reflect the
RBE of the different types and energies of radiation in producing stochastic
effects.  For radiations with a weighting factor greater than 1, the values
of RBE for deterministic effects are smaller than those for stochastic
effects.  The use of the equivalent dose to predict deterministic effects
for high LET radiations, e.g. neutrons, will thus lead to overestimates."

IAEA in Technical Report Series No. 211 states:  "The dose equivalent is
limited to radiation protection applications and may be used to compare
values of H with the applicable values of the dose equivalent limit.  It
should not be used in assessing the effects of high-level, accidental
exposures such as may be sustained during criticality accidents."  And in
another section:  "In nuclear accidents acute biological effects are
predominant and, as was stated earlier, the quality factors needed to
estimate dose equivalent are no longer valid.  In this case neutron doses
should be given in gray (Gy)...".

With respect to the question of the inappropriateness of using Sv instead of
Gy for criticality accident dosimetry, I'll defer to ICRU, ICRP, and IAEA.
Can we put this one to rest now, and stop talking Sv (or rem) in cases where
the units have no relevance?

And does anyone know what the latest estimates are for the doses (in
relevant quantities) these workers got?  That is, the neutron absorbed doses
and the photon absorbed doses?

Bruce Heinmiller CHP
heinmillerb@aecl.ca


> ----------
> From: 	Carroll,Raymond[SMTP:carrollrg@pgdp.usec.com]
> Reply To: 	radsafe@romulus.ehs.uiuc.edu
> Sent: 	Wednesday, October 06, 1999 11:18 AM
> To: 	Multiple recipients of list
> Subject: 	RE: S.Korea Launches Probe Into Nuclear Accident
> 
> One other little tid bit.  Quality factors are not applicable for high
> acute
> doses of radiation.  For more information you might want to research the
> NCRP and ICRP documents.
> 
> Ray Carroll
> carrollrg@pgdp.usec.com
> ___________________________________________________
> 
> -----Original Message-----
> From: Michael McNaughton [mailto:mcnaught@lanl.gov]
> Sent: Wednesday, October 06, 1999 10:09 AM
> To: Multiple recipients of list
> Subject: Re: S.Korea Launches Probe Into Nuclear Accident
> 
> 
> The LD50/60 is normally quoted in Gy, not Sv.
> 
> Assuming Hisashi Ouchi received 1.7 SV, and assuming a neutron quality
> factor of 10, one might guesstimate this is about 0.15 Gy gamma and 0.15
> Gy
> neutron. Would you expect this to be a fatal dose?
> 
> At 09:44 AM 10/6/99 -0500, you wrote:
> >It is unfortunate when even we in the nuclear industry confuse dose 
> >limits from a regulatory perspective with what is considered to be 
> >"safe". And how does one define safe anyway? This article refers to 
> >the 600 rem as being a fatal dose. Yet we have 2 Japanese workers 
> >still alive, yet very ill, receiving doses approaching 1700 rem, or 
> >higher. Statements such as quoted in this article, and in others from 
> >our profession only do harm. These statements do not take into 
> >account medical intervention, which significantly increases an 
> >individual's chances of surviving extremely high doses.
> 
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