40 research outputs found
2005- 2008 UNLV McNair Journal
Journal articles based on research conducted by undergraduate students in the McNair Scholars Program
Table of Contents
Biography of Dr. Ronald E. McNair
Statements:
Dr. Neal J. Smatresk, UNLV President
Dr. Juanita P. Fain, Vice President of Student Affairs
Dr. William W. Sullivan, Associate Vice President for Retention and Outreach
Mr. Keith Rogers, Deputy Executive Director of the Center for Academic Enrichment and Outreach
McNair Scholars Institute Staf
Velocity-selected production of 2S3 metastable positronium
Positronium in the 2 3 S metastable state exhibits a low electrical polarizability and a long lifetime (1140 ns), making it a promising candidate for interferometry experiments with a neutral matter-antimatter system. In the present work, 2 3 S positronium is produced, in the absence of an electric field, via spontaneous radiative decay from the 3 3 P level populated with a 205-nm UV laser pulse. Thanks to the short temporal length of the pulse, 1.5 ns full width at half maximum, different velocity populations of a positronium cloud emitted from a nanochanneled positron-positronium converter were selected by delaying the excitation pulse with respect to the production instant. 2 3 S positronium atoms with velocity tuned between 7
7 10 4 ms 121 and 10
7 10 4 ms 121 were thus produced. Depending on the selected velocity, a 2 3 S production efficiency ranging from 3c0.8% to 3c1.7%, with respect to the total amount of emitted positronium, was obtained. The observed results give a branching ratio for the 3 3 P-2 3 S spontaneous decay of (9.7 \ub1 2.7)%. The present velocity selection technique could allow one to produce an almost monochromatic beam of 3c1
7 10 3 2 3 S atoms with a velocity spread of <10 4 ms 121 and an angular divergence of 3c50 mrad
Techniques for production and detection of 23S positronium
In this work, we show recent measurements of 23S long-lived positronium production via spontaneous decay from the 33P level. The possibility to tune the velocity of the 23S positronium, excited following this scheme, is presented. In the light of these results, we discuss the use of the 33Pâ23S transition to realize a monochromatic pulsed 23S positronium beam with low angular divergence. Preliminary tests of 23S beam production are presented. The possibility to overcome the natural 33Pâ23S branching ratio via stimulated emission, and thus increasing the intensity of the 23S source, is also shown. A position-sensitive detector for a pulsed beam of positronium, with spatial resolution of â 90 ÎŒm, is finally described in view of its possible application for the spatial characterization of the 23S beam