Date of Award
Program or Major
Doctor of Philosophy
James J Connell
Moderate energy positrons (~few to 10 MeV) have seldom been observed in the Heliosphere, due largely to the lack of dedicated instruments. Deep-space measurements of these positrons would have implications in the study of Solar energetic particle events and the transport and modulation of Galactic cosmic rays in the Heliosphere. Positron Identification by Coincident Annihilation Photons (PICAP) is a detector scheme to measure these positrons by simultaneously detecting the two 0.511- MeV gamma-ray photons emitted from negatron-positron annihilation of stopping positrons. PICAP is intended for deep-space missions with severe limits on mass, power, and telemetry. This dissertation details the development and testing of a prototype to prove PICAP's viability and performance. Monte Carlo modeling provided expected instrument response. Based on the modeling, a prototype was built. On 1 June 2013, the prototype was tested at the Burr Proton Therapy Center to demonstrate PICAP's ability to discriminate protons from positrons (and electrons). Exposure to energetic protons ranging from 69.6 MeV through 214.9 MeV showed that protons were misidentified as electrons on the order of few per 100,000 and misidentified as positrons on the order of few per 1,000,000, indicating a high rejection rate for protons. On 9-10 December 2013, the prototype was tested at the Idaho Accelerator Center to determine the response to negatrons and positrons with energies between 4 and 9 MeV. Unforeseen experimental circumstances prevented event-by-event identification of particles, so a maximum likelihood statistical analysis was developed. We showed for several particle energies that positrons were identified with a greater than 5-sigma statistical accuracy. The probability of positron measurement was consistent with zero when exposed to negatrons and within a factor of two of the Monte Carlo data when exposed to positrons. Agreement between experimental and simulation data thus confirmed that PICAP can make the required measurements. As a result of this work, the PICAP's NASA Technology Readiness Level (TRL) was advanced from Level 3 to Level 5, where it can be proposed for future space missions.
Tran, Dan Lam, "Development and Testing of Positron Identification by Coincident Annihilation Photons
(PICAP)" (2019). Doctoral Dissertations. 2463.