RE: Neutron dose factor, comments

["Colvett, Robert D." <rdcolvett@tva.gov>]

Fully aware that I may not be fully aware of the question,
here is yet another look at the dependence of dose-equivalence on
neutron energy.

One of the considerations is the change of quality factor with
Linear Energy Transfer (LET), or dE/dx.  For protons, there 
is a peak of about 80 keV/micron at about 80 kev proton energy.
At higher energies, the dE/dx decreases, to 40 keV/micron
at about 500 keV, to 20 keV/micron at about 1.5 MeV, to
5 keV/micron at about 9 meV, and on down to the traditional
QF=1 value of 3.5 keV/micron near 15 MeV.  So the protons themselves
begin to look like ordinary electrons at higher energies.

Adding complication to this trend is the recoil of heavier nucleii.
There is a resonance for scatter on oxygen at about 430 keV,
and RBE studies tend to show a maximum there, where the proton
dE/dx is still fairly high.  At energies > 10 meV, spallation reactions
can begin to happen, with the overall increase of effective dE/dx
	due to splashed-out nuclear fragments, especially alpha particles.

	numbers from ICRU 49, mostly

	r d colvett
	tva
	muscle shoals, al
	rdcolvett@tva.gov

> ----------
> From: 	Mike McNaughton[SMTP:mcnaught@lanl.gov]
> Sent: 	Wednesday, February 17, 1999 11:26 AM
> To: 	Multiple recipients of list
> Subject: 	Re: Neutron dose factor, comments
> 
> Thank you, Les, for your detailed response on neutron dose calculations.
> Are you familiar with the calculations of Leuthold, which drive ICRP60?
> (see ICRP page 85.) In particular, what causes Q to be the same, near 100
> keV, as the Q for alpha particles? Does this mean the dose from (n,g) is
> negligible near 100 keV?
> 
> "Shlala gashle" (Zulu greeting, meaning "Stay safe")
> mike (mcnaught@LANL.GOV)
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