Measurement of the ^242mAm Neutron Fission Cross Section

The fission cross section of ^242mAm has been measured from 0.005 eV to 20 MeV using time-of-flight techniques at the Oak Ridge Electron Linear Accelerator. A hemispherical plate fission ionization chamber with five pairs of plates contained three deposits totaling 507 μg of ^242mAm, one deposit of 168 μg ²³⁵U, and a “weightless” deposit of ²⁵²Cf, which served as a monitor of chamber performance. The fission of ²³⁵U, served as the cross-section standard for energies above 101 keV while ⁶Li(n,α), normalized to ²³⁵U fission in the 7.8- to 11.0-eV interval, served as a shape standard below 101 keV. Approximately 360 h of data were obtained at a flight path distance of 9.1 m, primarily with 40-ns bursts. Particular attention was paid to correction of backgrounds, especially inscattered-neutron-induced events. The fission resonance integral was found to be 1800 ± 65 b.