Technical Merit

1. Title:Development of a New Method for Interrogating Special Nuclear Materials based upon Polarized (g,n)AsymmetriesOrg/PI:DukeUniversity / Henry R. Weller • Broader Impact • Three graduate students (Duke, UNC-CH and NCCU) will obtain degrees based upon these studies. Two postdocs are actively involved and three undergraduate students participated in the summer of 2011. • A new collaboration with a theorist at LBNL was initiated this year. • Results were or will be reported at APS Meetings in May, 2011 and October, 2012-- and at an APS organized Press Conference in April, 2011. • Shown above are recent measurements of the ratio of prompt fission neutron yields parallel and perpendicular to the plane of photon beam polarization, illustrating a new technique to differentiate 235U from 238U. Technical Merit The 100% linearly polarized beams from HIgS and an 18- element neutron detector array are being used to measure polarization asymmetries in (g,fission) and (g,n) reactions for the first time. Technical Approach We are measuring the ratios of neutrons emitted parallel vs. perpendicular to the direction of polarization of the beam for both fissionable and non-fissionable nuclei. Measurements on 17 targets have been completed to date at energies above (g,n) threshold while fissionable nuclei are being studied below threshold where all neutrons are from fission. Schedule: • Duration: 60 months • Current month of effort: 35 • Major Milestones / Accomplishments • We have discovered that polarization ratios of fission neutrons from odd-A targets (235U, 239Pu) are close to 1.0, while those from even-A targets (238U, 232Th) are nearly 3.0. Non-fissionable targets show unique signatures at higher beam energies. • Team • Co-PIs: M. W. Ahmed and Y. K. Wu; Collaborating Institutions: GWU, JMU, NCCU, UNC-CH, LBNL. • Last updated on: 07/12/2012 • Last updated on: mm/dd/yyyy