|Student Name:||1st Lt Stefan B. Fagan-Kelly|
|Thesis:||Three Dimensional Positron Annihilation Momentum Spectroscopy of Lithium Tetraborate Crystals|
|Location:||Bldg 640, ENP Conference Room|
|Date & Time:||02/21/2013 at 1100|
|Abstract:|| Previous endeavors into Positron Annihilation Spectroscopy (PAS) at AFIT have resulted in the design and characterization of a second-generation Three-Dimensional Positron Annihilation Momentum Spectroscopy System (3DPAMSS) which combines Two-Dimensional Angular Correlation of Annihilation Radiation (2D ACAR) and Coincident Doppler Broadening of Annihilation Radiation (CDBAR) in order to measure electron momentum distributions in samples and thus characterize material defects. The focus of this research in particular is to nondestructively measure negative defects in the crystal lattice of copper-doped, silver-doped, and undoped lithium tetraborate using a Na-22 source and two high-purity germanium (HpGe) position-resolvable strip detectors. Lithium tetraborate is a candidate for being a novel neutron detector material and characterizing its crystal structure is necessary to fully understand its properties. Several angular deviation and differential energy features are noted, which are translated to potential electron momentum distribution features.