Total Neutron Cross Section of ²²⁸Th for the 1.9- and 7.5-eV Resonances

The total neutron cross section of ²²⁸Th has been measured in the regions of 1.9 and 7.5 eV, with the Materials Testing Reactor (MTR) fast chopper. The ²²⁸Th occurred as a contaminant in several samples of the parent ²³²U, on which cross-section measurements were being made at various decay times. For the two resonances which grew in with enough prominence to allow analysis, the resonance parameters deduced are: 1. E₀ = 1.896 ± 0.002 eV, Γγ = 36 ± 2 mV, = 0.57 ± 0.04 mV, 2. E₀ = 7.55 ± 0.02 eV, Γγ = 70 ± 30 mV, = 0.44 ± 0.05 mV.