New Facility a Positive for Positron Spectroscopy Advances Published March 4, 2010 By Shelly Bloomfield Munitions EGLIN AIR FORCE BASE, Florida -- Air Force Research Laboratory researchers at Eglin Air Force Base, Florida, demonstrated initial operational capability of a positron spectroscopy lab that promises to shed light on atomic and nanoscale flaws existing in energetic materials, which are critical constituents of insensitive munitions. The new facility--where researchers will have access to Positron Annihilation Lifetime Spectroscopy and Two-Dimensional Doppler Broadening of Annihilation Radiation technologies--will facilitate efforts to obtain crucial information regarding the concentration, morphology, and size of the defects and voids found in assorted energetic materials of importance to warfighter capability development. When a positron (the antiparticle of an electron) enters a material, it tends to localize in open volumes. After a short time, the positron (along with its partner electron) annihilates, producing gamma rays in the process. Using scintillation and semiconductor detectors to measure the time of arrival and precise energy of the annihilation-produced gamma rays enables positron lifetime and partner-electron momentum to be determined. Since the positron is a highly interactive probe, these resulting gamma ray spectra are very sensitive to the size and makeup of defects and voids present in the material. Thus, while researchers have for decades used positrons to nondestructively probe the defect structure of semiconductors, metals, and polymers, they have only recently begun using them to examine energetic materials (explosives, propellants, fuels, and so on). It is well known that the mechanical properties, reaction dynamics, and initiation thresholds of energetic materials are profoundly affected by the presence of defects and voids in those materials. The role that such flaws play at the submicron scale, especially in nanoengineered materials, is unclear. This poor understanding is largely due to the difficulty of probing, in a nondestructive way, such length scales in the bulk. Accordingly, experts anticipate that PALS and 2D-DBAR will prove invaluable in refining energetic materials processing methods, as well as expounding the importance of nanodefects in insensitive munitions development. The PALS and 2D-DBAR tools represent short-term payoff products precipitated by AFRL's long-term research efforts towards practical positron energy conversion. The newly demonstrated positron spectroscopy lab promoting the use of this technology is unique in the Department of Defense and will undoubtedly serve as a tremendous resource for the characterization of a wide range of materials.