Total Neutron Cross Section of Pa231

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Abstract
The total cross section for Pa231 was measured from 0.01 ev to 2 kev, with the use of the Materials Testing Reactor fast chopper with resolutions from 0.040 to 2.0 µsec/meter. The Breit-Wigner resonance parameters have been obtained for the resonances below 11.0 ev. These measurements were made with samples prepared from 0.558 gm of Pa2O5. Weighting the level spacings inversely as 2J + 1 gives the average observed level spacings per spin state of 0.72 and 1.2 ev. This is one of the smallest spacings observed in any isotope. The average parameters give a value of 0.63 × 10−4 for the s-wave neutron strength function . A linear least squares fit to the data between 0.015 and 0.03 ev gives a value of 211 ± 2 barns for the thermal cross section. The resonance absorption integral (for neutrons with energies > 0.1 ev) is 1560 ± 55 barns, with a contribution of approximately 65% from the 0.396 ev resonance.

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