Speaker
Description
Photonuclear reactions offer a unique probe of the nucleus due to lack of hadronic processes in the entrance channel. This is of particular interest for studying the prompt neutrons emitted during fission, which is more typically initiated with neutrons. Two types of measurements of prompt neutrons emitted from photon-induced fission will be presented.
At photon beam energies between about 10 and 15 MeV where the fission cross section is sufficiently high, active targets were used to tag fission events associated with detection of prompt neutrons. The $\gamma$-ray beam is nearly monoenergetic and pulsed with a width of 0.3 ns FWHM and a period of 179.2 ns. The neutrons were detected in an array of liquid organic scintillators, and the kinetic energy of each detected neutron was determined using time-of-flight methods.
Measurements below 10 MeV are motivated by efforts to develop bremsstrahlung-based active interrogation systems for detecting special nuclear materials for national security and non-proliferation purposes. Due to the substantially lower cross sections at these energies than in the resonance energy region above, these measurements were performed using larger passive targets with the same neutron detector array used in the tagged fission setup.
The experimental techniques used to perform the measurements will be discussed, and preliminary results obtained at beam energies from 5-16 MeV will be presented.
This research is supported in part by the US Department of Homeland Security under Grant No. 20CWDARI00035-01-00, the National Nuclear Security Administration under Grant Nos. DE-NA0003887 and DE-NA0004069, and by the US Department of Energy under Grant No. DE-FG02-97ER41033.
