Re: PEACEMAKER - Some Answers

["David W. Lee" <lee_david_w@lanl.gov>]

Dale:

	I also will be interested to read other RADSAFER responses to you
QUESTION.  As for myself, I'm not so sure that your stated reason why the
QF goes to 1 is the real reason why we speak in terms of "rads" at high
doses and in "rem" at low doses.  Your statement that QF goes to 1, to me,
is just another way of stating that we talk in terms of rads at high doses,
not in rem.  To my understanding, the use of Quality Factors has meaning
only when one talks in terms of chronic, certainly non-lethal rad doses of
whole-body radiation where the person sustaining the dose in "rads" has a
sufficiently long period of life expectancy left to manifest radiation
effects incident to the rad dose sustained, if indeed there will be any
radiation effects down the road.

	But if the individual sustains a truly life-threatening, acute whole-body
dose, say 500 rads, which is the approximate LD 50/30 for humans, there is
no point in speaking in terms of rem, because the individual may die
(within 30--90 days)--a time period sufficiently short that worrying about
the longer-term effects, in terms of rem, of the person's originally
sustained rad dose, is virtually meaningless.  The individual, due to the
acute radiation syndrome short-term and life-threatening effects of the 500
rad WB dose, simply does not have sufficient life expectancy left to worry
about the longer-term effects of his/her rem dose.

	Thus, as to when a rad of neutrons becomes biologically equivalent to a
rad of photons, considering that the biological end-point is short-term
death, I would say that the number of rads where this would occur would be
somewhere in the neighborhood of 800 rads, which is a whole-body dose above
which many clinicians agree that the human body begins to cross the grey
threshold from the hematopoietic to the gastrointestinal phase of the acute
radiation syndrome--the GI phase being one of virtually 100% mortality,
even with heroic (ineffective) medical care.  Even the Chernobyl fireman
who sustained the highest WB dose from which a human has ever survived
(with much medical care) sustained only a little over 800 rads; in other
words, clinically, he was at the very high end of the hematopoietic phase.
The fireman's other colleagues who sustained higher doses died of the GI
phase of the acute radiation syndrome.

Best regards  David

  



At 02:13 PM 04-11-97 -0600, you wrote:
>My understanding is that Quality Factor goes to 1 at high dose, because
>the low LET/high cell percentage vs. high LET/low cell hit percentages
>converge to give similar ionization densities.  QUESTION: For all
>of you microdosimetry experts out there, at about what number of rads
>does it not make a difference between a neutron and a photon?
>
>Dale
>
>
David W. Lee
Los Alamos National Laboratory
Radiation Protection Services Group (ESH-12)
PO Box 1663, MS K483
Los Alamos, NM  87545
PH:   (505) 667-8085
FAX:  (505) 667-9726
lee_david_w@lanl.gov