The Slow Neutron Cross Sections of Indium, Gold, Silver, Antimony, Lithium, and Mercury as Measured with a Neutron Beam Spectrometer

Abstract

The variations of the slow neutron transmissions of In, Au, Ag, Sb, Li, and Hg have been investigated as a function of the time-of-flight of the incident neutrons for a 5.4-meter path by use of a neutron beam spectrometer. A method of analysis is developed for determining $E_0$ and ${\sigma }_0{\Gamma }^2$ for resonances above 1 ev based on the experimental transmission curves and the Breit-Wigner theory. The positions of the levels located, listed in order of importance for each element, are: In, (1.44±0.04) ev; Au, (4.8±0.2) ev; Ag, (5.11±0.2) ev, (13.7±1) ev, and (43±5) ev; Sb, (6.3±0.5) ev, (19.2±1.0) ev, and indications of other unresolved levels in the region of 50 to 500 ev; Li, only a $\frac{1}{v}$ cross section; Hg, a negative level at (-2.0±0.2 ev) and indications of unresolved positive levels above 25 ev. In the thermal region, the Ag, Sb and Li cross-section curves can be resolved into the sum of a constant term and a $\frac{1}{v}$ term. If $E$ is the neutron energy in ev, these are: Ag: $\left[\right(9.05\mathrm{}\pm 0.10)E^{-\frac{1}{2}}+(6.6\mathrm{}\pm 0.5\left)\right]\times {10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$/atom; Sb: $\left[\right(0.64\mathrm{}\pm 0.02)E^{-\frac{1}{2}}+(4.2\mathrm{}\pm 0.3\left)\right]\times {10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$/atom; Li: $\left[\right(11.5\mathrm{}\pm 0.2)E^{-\frac{1}{2}}+(1.7\mathrm{}\pm 0.2\left)\right]\times {10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$/atom; LiF was used in the Li measurements and a value 2.5×${10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$/atom has been deducted for the F. The Hg cross section below 5 ev was well matched by the relation $(64\mathrm{}\pm 3)E^{-\frac{1}{2}}{\left(\frac{1+E}{2.0}\right)}^{-2\mathrm{}}\times {10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$/atom.