Amm242fission cross section

Abstract

The neutron-induced fission cross section of $^{242}\mathrm{Am}^{m}$ has been measured over the energy region from ${10}^{\ensuremath{-}3}$ eV to \ensuremath{\sim}20 MeV in a series of experiments utilizing a linac-produced "white" neutron source and a monoenergetic source of 14.1 MeV neutrons. The cross section was measured relative to that of $^{235}\mathrm{U}$ in the thermal (0.001 to \ensuremath{\sim}3 eV) and high energy (1 keV to \ensuremath{\sim}20 MeV) regions and normalized to the ENDF/B-V $^{235}\mathrm{U}(\mathrm{n},f)$ evaluated cross section. In the resonance energy region (0.5 eV to 10 keV) the neutron flux was measured using thin lithium glass scintillators and the relative cross section thus obtained was normalized to the thermal energy measurement. This procedure allowed a consistency check between the thermal and high energy data. The cross section data have a statistical accuracy of \ensuremath{\sim}0.5% at thermal energies and in the 1-MeV energy region, and a systematic uncertainty of \ensuremath{\sim}5%. We confirmed that $^{242}\mathrm{Am}^{m}$ has the largest thermal fission cross section known with a 2200 m/sec value of 6328 b. Results of a Breit-Wigner sum-of-single-levels analysis of 48 fission resonances up to 20 eV are presented and the connection of these resonance properties to the large thermal cross section is discussed. Our measurements are compared with previously reported results.