SURVEY METHODS FOR NEUTRON FIELDS Page: 4 of 37
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.UC L-1635
It is generally understood t1e t the reason for the greater biological
damage associated with neutron-produced ionization compared to that from
X-rays or gamma rays lies in the matter of specific ionization. Along the
tracks of recoil and secondary charged nuclear particles from neutron inter-
actions the ionization per unit path length io typically 100 times that along
the tracks of the Compton- and photo-electrons produced by X-rays and gamma
rays. So even though the total energy loss per unit mass of medium were the
same, these differences in local concentration of the effects will produce
different degrees of damage to the organism. These same differences in
specific ionization provide a basis for the selective detection of fast neutron
effects in the presence of a gama ray background.
Furthermore, the development in recent years of accelerators delivering
nuclear particles with energies extending into the hundreds of Mev has intro-
duced a few special considerations. The high-energy neutrons from such
machines almost completely dominate the shielding problem, being much more
penetrating than any gamma radiation. Also such neutrons are capable of pro-,
ducing nuclear "stare" in which a large fraction of the neutron energy may be
delivered, into a small volume of space in the form of high-energy nuclear
fragments. The quantitative, selective detection of neutrons of these energies
requires instruments quite distinct from those empdyead in the "fast'* region.
* For the purposes of this discussion, the term "high energy neutrons' will mean
those with kinetic energies greater than typical nuclear binding energies for
a neutron. Thus, very roughly, 'feet neutrons" will apply to energies above
the capture resonance region and up to. say 15 Mev. 'High energy' will apply
from 15 or 20 idev on up in energy.-3-
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Moyer, B.J. SURVEY METHODS FOR NEUTRON FIELDS, report, January 11, 1952; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc833023/m1/4/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.