Use of nuclear reaction models in cross section calculations Page: 4 of 26
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The first transparency summarizes these requirements. Global optical
parameters for alpha particles, Drotons and neutrons have been widely used
in calculating transmission coefficients, but appropriate parameters are
more difficult to find for deuterons, helium-3, or tritons. For nuclei in
the range A > 40, these latter three channels typically represent less than
27 of the decay width and can be ignored without affecting the oroton,
alpha or neutron cross sections, but for A < 25 these channels could be
important (depending on the Q values). Also, for light nuclei the use of
averaged level density parameters may not be appropriate. Specific level
schemes are required in situations where the level density is small. I
will not discuss these calculations in detail because a previous speaker
has discussed the Hauser-Feshbach formalism.
Although the remaining processes comprise a small fraction (<.2) of
the reaction cross section they are of considerable imortance. For example,
if one looks at the neutron spectrum produced by 14-MeV neutron bombardment
of Fe, it can be seen that only the low energy portion of the spectrum is
fit by a compound nuclear calculation. From a neutron transport standpoint,
a factor of five to ten error for inelastic neutrons above 8 MeV could be
Is there a procedure which can be used to predict the inelastic spectrum
above 6 MeV on the basis of nuclear reaction systematics? To answer this
question, we first examine (p,p') spectra on a number of targets at 14 MeV.
The next transparency shows the (p,p') cross sections for a number of Ti and
Mo isotopes. Each isotope chain includes one element for which the neutron
number is magic. Although in these cases the first 2+ state is populated
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Grimes, S.M. Use of nuclear reaction models in cross section calculations, article, March 1975; Livermore, California. (https://digital.library.unt.edu/ark:/67531/metadc1015937/m1/4/: accessed June 17, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.