Development and Optimization of a Positron Annihilation Lifetime Spectrometer to Measure Nanoscale Defects in Solids and Borane Cage Molecules in Aqueous Nitrate Solutions
Abstract
A Positron Annihilation Lifetime Spectroscopy (PALS) system was developed and tested. PALS has the capability to characterize negatively charged defects and voids in materials such as explosives. The timing resolution of the optimized system is 197 +or- 14 ps as measured with a known (60)Co source. A single-crystal tungsten sample was used to confirm the system calibration resulting in a lifetime of 101 +or- 2 ps (as compared to 105 +or- 5 ps in the literature (16)). The PALS system was then used to compare the differences between as grown and neutron-irradiated single crystal silicon carbide (SiC), illustrating that neutron bombardment of SiC results in the creation of silicon vacancies in the material. The lifetime of a positron associated with a boron cage anion, dodecahydrododecaborate in aqueous nitrate solution, was 277 +or- 10 ps, compared with previous measurements of the cage compound in solid state which yielded 268 +or- 8 ps. Competition for positrons between nitrate anion and the boron cage was measured.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 2008
- Accession Number
- ADA483604
Entities
People
- Matthew A. Ross
Organizations
- Air Force Institute of Technology