Resulting Neutron Spectrum Research Articles

TheMn55(p,n)Fe55Neutron Spectrum

A thin (20-kev) target of manganese on a tantalum backing was bombarded by monoenergetic protons of 2.97, 3.42, and 3.77 Mev from the Rockefeller electrostatic generator. Nuclear emulsion plates (Eastman NTB, 200 microns thickness) were mounted 15 cm from the target at 0\ifmmode^\circ\else\textdegree\fi{} and 90\ifmmode^\circ\else\textdegree\fi{} with respect to the incident proton beam. The resulting neutron spectra, obtained from the analysis of 2400 proton recoil tracks, show well-defined groups which correspond to excited states in ${\mathrm{Fe}}^{55}$ at 0.42, 0.94, 1.36, and 2.08 Mev. The group corresponding to the level at 1.36 Mev has an unusually large width indicating that this level is complex. The $Q$-value for the ground-state reaction was measured to be -1.05\ifmmode\pm\else\textpm\fi{}0.05 Mev, giving the threshold for neutron production as 1.07\ifmmode\pm\else\textpm\fi{}0.05 Mev. Levels in ${\mathrm{Fe}}^{55}$ at 0.935 and 1.41 Mev have been found by Deutsch and Hedgran from a study of the decay scheme of ${\mathrm{Co}}^{55}$. These levels correspond closely to two of the levels reported here.

The Inelastic Scattering of 15-Mev Neutrons by Lead, Iron, and Aluminum

A tritium-zirconium target bombarded by 1.0-Mev deuterons from the Rockefeller electrostatic generator was used as a source of high energy (\ensuremath{\sim}15-Mev) neutrons. This source was surrounded by lead, iron, and aluminum scatterers with dimensions of approximately one mean free path for inelastic scattering. The resulting neutron spectra were measured by means of proton recoils in photographic emulsions. An exposure without scatterer permitted an evaluation of the upper limit for the neutron background. The spectra indicate that most of the neutrons are inelastically scattered to energies below 3 Mev in the case of the lead and iron scatterers and to below 5 Mev with the aluminum scatterer. The data can be represented by a curve of the form (const $E{e}^{\ensuremath{-}\frac{E}{T}}$) as predicted by the Weisskopf statistical theory. The values obtained for the nuclear temperatures, $T$, are 0.7, 0.6, and 1.1 Mev for lead, iron, and aluminum, respectively. The fact that the measured temperatures for iron and lead are approximately the same supports the hypothesis that lead nuclei have a closed shell structure and therefore have properties similar to much lighter nuclei.