Accession Number : ADA566902


Title :   Efficient Cryosolid Positron Moderators


Descriptive Note : Final rept. 1 Oct 2005-1 Aug 2012


Corporate Author : AIR FORCE RESEARCH LAB EGLIN AFB FL MUNITIONS DIRECTORATE


Personal Author(s) : Fajardo, Mario E ; Lindsay, C M ; Molek, Christopher D


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a566902.pdf


Report Date : Aug 2012


Pagination or Media Count : 105


Abstract : This report documents an in-house experimental effort to improve upon the ε 1% efficiency of state-of-the-art cryogenic solid neon positron moderators. We detail our rationale for why we expected an order-of-magnitude higher positron moderation efficiency from Rapid Vapor Deposited cryogenic parahydrogen solids. We describe our integration of a Matrix Isolation Spectroscopy capability into our Positron Moderation apparatus, which enables spectroscopic characterization of the cryogenic moderators. Despite all our hopes and expectations to the contrary, solid parahydrogen is not a positron moderator. Indeed, a ≈ 15-nm-thick layer of solid normal hydrogen is sufficient to kill half the flux of slow positrons emerging from a working solid neon moderator. We also report results from experiments on other rare gas solid positron moderators, on moderators overcoated with layers of other molecular solids, and on moderators containing deliberately included isolated dopants. We present our methods and data in great detail to facilitate the continuation and extension of these experiments by other researchers.


Descriptors :   *CRYOGENICS , *POSITRONS , *SPECTROSCOPY , EFFICIENCY , FLUX(RATE) , HYDROGEN , INTEGRATION , ISOLATION , KILL PROBABILITIES , LAYERS , MATRIX THEORY , MOLECULAR PROPERTIES , NEON , REPORTS , SOLIDIFIED GASES , SOLIDS


Subject Categories : Nuclear Physics & Elementary Particle Physics


Distribution Statement : APPROVED FOR PUBLIC RELEASE