Accession Number:

ADA547542

Title:

Matrix Isolation Spectroscopy Applied to Positron Moderatioin in Cryogenic Solids

Descriptive Note:

Briefing charts

Corporate Author:

AIR FORCE RESEARCH LAB EGLIN AFB FL MUNITIONS DIRECTORATE

Report Date:

2011-07-01

Pagination or Media Count:

40.0

Abstract:

We report results of Matrix Isolation Spectroscopy MIS experiments performed on working cryogenic rare gas solid RGS positron e moderators. The e is the antiparticle to the electron,1-3 and positrons are produced by energetic processes that result in very broad kinetic energy distributions KEDs - typically spanning hundreds of thousands of electron volts eV. Trapping and manipulating e with electromagnetic fields requires narrowing these KEDs below a few eV, which is accomplished via velocity-dependent interactions in a normal matter moderator. A fast e entering a wide bandgap dielectric RGS moderator slows rapidly within the first picosecond, producing a track of ionized and electronically excited species. However, once KEe drops below the 10 eV minimum required for generating such excitations, these interactions abruptly switch off, and the e enters a phase of hyperthermal diffusion that can last for nanoseconds. Positrons that reach a free surface of the moderator before annihilating with an electron may escape into vacuum where they can be manipulated. The best known e moderator is cryogenic solid Ne, which still only delivers efficiencies 1 the other 99 of the nascent fast e are wasted. Additionally, the RGS moderator efficiency is known to decrease during operation, which is attributed variously to the buildup of radiation damage, andor to contamination of the moderator surface by residual gas deposition. We constructed a novel apparatus that permits optical access to a working cryogenic solid moderator. Our original motivation was to test our hypothesis that solid parahydrogen pH2 should be an even better e moderator than solid Ne, while simultaneously monitoring the condition of the moderators by infrared IR absorption spectroscopy. Unfortunately, the performance of our orthopara hydrogen converter op convert

Subject Categories:

  • Radiobiology
  • Physical Chemistry

Distribution Statement:

APPROVED FOR PUBLIC RELEASE