Slow Neutron Resonances in Indium

Abstract

The neutron spectrometer previously described has been modified and improved to permit the use of 12 detector timing channels. It has been used to determine the neutron cross section for absorption in indium as a function of neutron energy in the range extending from 0.017 to 50 ev. Five absorber thicknesses were used in the measurements. These were 0.0227, 0.246, 0.907, 2.754, and 4.05 g/${\mathrm{cm}}^2$. The strong resonance previously observed was found to be located at 1.44 ev and two weaker resonances were found at about 3.7 and 9.0 ev. The resonance at 1.44 ev was carefully studied. An analysis was made to take into consideration the effective resolution and to determine the parameters of the Breit-Wigner one-level formula which best describe the resonance. The constants which provided the best fit with the data were ${\sigma }_0=26,400\mathrm{}\times {10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$ and $\Gamma =0.085\mathrm{}$ ev. The resolution did not permit a similar analysis for the levels at higher energy and it was only possible to place rough lower limits for the values of the cross section at resonance.