NEutron QF

[Sunil C Nair <sunil@tifr.res.in>]

Hi All

 My original query about high energy neutron having less QF evoked a
general response of absorption coming down as neutron energy, along with
the QF. I will add a bit more to the confusion :-)

In the energy range 2MeV to 20MeV, (where the QF is less than the 100KeV
to 2MeV range) N(n,p), H(n,gamma) and elastic collisions with Hydrogen
still dominate the contribution to the dose. Thus we are essentially
dealing with the same protons (either recoil or reaction product) with
more energy, and gamma photons. Now, QF depends on the LET of the
secondary particles that deposit energy in the tissue. Does the LET
changes so drastically in such short span of energy?  

If  as absorption cross section does come down, as suggested by Scott
Schwan and  Neal Zapp, how  is the dose per neutron an increasing function
all the way ? I have found tables and figures in literature to show that
dose increase as neutron energy.  (1). Accelerator Health Physics,
Patterson & Thomas, page 70, fig 2.12.  (2). is "A guide to radiation and
radioactivity levels near high energy particle accelerators by A.H.
Sullivan, page 27, Fig 1.17). This is true even for energies where
spallation is negligible. THus, while the dose goes up, QF comes down and
remain steady.

Perhaps, Robert Clovett's posting yesterday may provide a clue
Any further thoughts/comments ?

Regards
Sunil Nair
sunil@tifr.res.in


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