14-18 MeV total neutron cross sections of hydrogen atom, hydrogen, lithium-7, beryllium-9, boron-10, boron-11, carbon-12, carbon-16, magnesium, aluminum-27, and sulfur-32
Cook, Charles Falk
Doctor of Philosophy
Measurements of total neutron cross sections for nuclei using fast neutrons of various energies have been previously reported. Several of these used neutrons which were not monoenergetic. However, with the advent of monoenergetic neutrons from the reaction T(d,n)He4, investigations have been reported giving total neutron cross sections at 14 Mev using monoenergetic neutrons in "good" geometry to various accuracies. Of these various reports, the data of Coon, Graves, and Barschall point to deviations from the schematic theory of nuclear cross sections proposed by Feshbach and Weisskopf for the lighter elements as well as some of the heavier elements. A systematic deviation from a plot of the equation sT2p =kA13 sT= total neutron cross section A= atomic weight was observed for the elements Be9, B10, B11, and C12. For these four elements the cross section was observed to be a decreasing function of the atomic weight. This effect is consistent with the data of Lasday and Goodman for Be9 and C12. Neither of the latter did the boron isotopes. The data of Lasday and Goodman also represents 14 Mev total neutron cross sections. Of these investigations, no one group carried out cross section measurements at more than one particular neutron energy. It is of interest to see over what energy range these systematic deviations appear. The results of Cook, et al., show that at 90 Mev the total neutron cross section for H, D, L1 7, Be9, C12 are increasing with atomic weight. This indicates that at some point in the energy range 14 to 90 Mev these deviations disappear. The investigations carried out here are measurements of total neutron cross sections for some of the light elements over the energy range 14 to 18 Mev. In addition to checking for a systematic deviation similar to that found by Coon, et al., considerable attention was given to determination of the neutron-proton total cross section over the above energy range.