Measurements of Neutron-induced Fission Cross Section of Americium-243 from Thermal Neutron Energy to 15 keV Using Lead Slowing-down Spectrometer and Thermal Neutron Facility

Abstract

The neutron-induced fission cross section of ²⁴³Am was measured relative to that of ²³⁵U from thermal neutron energy to 15 keV making use of a double fission chamber with ²⁴³Am and ²³⁵U electrodeposited layers.

The data above 0.05 eV were measured using a lead slowing-down spectrometer coupled to an electron linear accelerator. A relative measurement to the ¹⁰B(n, α) reaction was also made using a BF₃ counter at energies below 1 keV, and normalized to the absolute value obtained by using the cross section of the 235U(n,/) reaction between 200eV and IkeV. The existing experimental data by Wisshak and Käppeler, and by Knitter and Budtz-Jørgensen are in general agreement with the current measurement in the relevant energy region. However, the data by Seeger are considerably higher. The evaluated nuclear data in JENDL-3.2, ENDF/B-VI and JEF-2.2, whose data were broadened by the energy resolution function of the spectrometer, have been compared with the measured result.

The fission cross section for thermal neutrons was measured in a neutron field with a pure Maxwellian spectrum. The derived result at 0.0253 eV is 81.3±2.5 mb. The data by Wagemans et al. and in ENDF/B-VI are close to the current measurement. However, the values by Asghar et al., Gavrilov et al. and Mughabghab, and the evaluated data in JENDL-3.2 and JEF-2.2 are discrepant from the current result by a factor of 1.4 to 2.4.

KEYWORDS:

• neutron-induced fission cross sections
• measurement
• americium 243
• resonance energy region
• lead slowing-down spectrometer
• back-to-back type double fission chamber
• thermal neutron cross section
• Maxwellian distribution
• JENDL-3.2
• ENDF/B-VI
• JEF-2.2