Neutron Capture and Fission Cross Section of ²⁴³Am in the Energy Range from 5 to 250 keV

The neutron capture and subthreshold fission cross section of ²⁴³Am was measured in the energy range from 5 to 250 keV using ¹⁹⁷Au and ²³⁵U as the respective standards. Neutrons were produced via the ⁷Li(p,n) and the T(p,n) reaction with the Karlsruhe 3-MV pulsed Van de Graaff accelerator. Capture events were detected by two Moxon-Rae detectors with graphite and bismuth graphite converters, respectively. Fission events were registered by an Ne-213 liquid scintillator with pulse-shape discriminator equipment. Flight paths as short as 50 to 70 mm were used to obtain an optimum signal-to-background ratio. After correction for the different efficiency of the individual converter materials, the capture cross section could be determined with a total uncertainty of 3 to 6%. The respective values for the fission cross section are 8 to 12%. The results are compared to predictions of recent evaluations, which in some cases are severely discrepant.