Instrumentation for fission cross section measurements on actinides

The paper describes three developments in instrumentation for actinide fission cross section measurements at ORNL. Two of these are related to the problem of detecting a few fission events in the presence of an extremely large alpha background. Time-of-flight measurements of neutron fission cross sections on highly alpha active actinide samples at electron linear accelerators have been hindered by pileup of alpha pulses in the amplifier, a noise contribution which is normally overwhelming. In the past, such measurements could only be made using underground nuclear explosions; indeed, much of the present knowledge of the fission cross sections of highly alpha-active nuclides comes from such measurements. The third development is an improved neutron beam monitor for time-of-flight measurements