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RE: Units for Criticality Accident
The Na-23(n,gamma) activation probability is remarkably flat with incident
neutron energy, which makes the body a good scaled integrator of neutron
fluence (after correction for factors like body orientation and floor
scatter), but going from neutron fluence to neutron absorbed dose requires a
direct or indirect knowledge of the neutron spectrum.
--Bruce.
> ----------
> From: David_S_Hyder@RL.gov[SMTP:David_S_Hyder@RL.gov]
> Reply To: radsafe@romulus.ehs.uiuc.edu
> Sent: Wednesday, October 06, 1999 1:52 PM
> To: Multiple recipients of list
> Subject: RE: Units for Criticality Accident
>
> Bruce,
>
> I absolutely agree with you. However, I still have not seen any data on
> how the workers dose was determined. I doubt that personal nuclear
> accident dosimetry was worn as a criticality accident was determined to
> be a "non-credible" event. The workers dosimetry may have been read
> but, was a suitable algorithm available, based on the neutron energies
> of this "non-credible" event. I assumed that the doctors are basing the
> dose estimate on the physical state of their patients (i.e. blood
> chemistry). The doctors may have done the same as I did on Thursday,
> referenced a chart based on onset of symptoms.
>
> I'm not an expert, could the doctors use the sodium activation in the
> patients blood, corrected for decay, to determine the neutron flux and
> thus determine neutron dose?
>
> I'm just glad that I'm getting some information, I would imagine that
> the stress level is pretty high over there right now. The final report
> should get the numbers and units correct.
>
> David Hyder
> David_S_Hyder@rl.gov
> Health Physicist
> Hanford Facility Evaluation Board
>
> > -----Original Message-----
> > From: Heinmiller, Bruce [SMTP:heinmillerb@aecl.ca]
> > Sent: Wednesday, October 06, 1999 9:24 AM
> > To: Multiple recipients of list
> > Subject: RE: S.Korea Launches Probe Into Nuclear Accident
> >
> > 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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information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html