Speaker
W. Clarke Smith
(George Washington University)
Description
Azimuthal asymmetries in neutron yields produced by bombarding targets with linearly polarized photons via (gamma,n), (gamma,2n), and (gamma,f) reactions are being investigated as a possible means of identifying various nuclear isotopes. The High Intensity gamma-ray Source (HIgS) at Duke University provides nearly monochromatic, circularly or linearly polarized gamma rays with high intensity by Compton backscattering free-electron-laser photons from stored electrons. Linearly polarized gamma rays produced by HIgS were incident on {nat}Cd, {nat}Sn, and 181Ta targets at six energies E_gamma between 11.0 and 15.5 MeV and emitted neutrons were detected both parallel and perpendicular to the plane of polarization by an array of 18 liquid-scintillator detectors at angles in the range theta=55 deg--142 deg. Detected neutrons were distinguished from Compton scattered photons by pulse-shape-discrimination and timing cuts, and their energies (E_n) were determined using time-of-flight information over a 0.5 m flight path. The characteristic plots of R_n, the ratio of neutron counts parallel to neutron counts perpendicular to the plane of the incident gamma-ray polarization, against E_n were constructed for each value of E_gamma and theta and then compared to those for other targets studied at HIgS, including fissile nuclei 235U and 238U.
Co-author
Gerald Feldman
(George Washington University)
