<p> The objective of the proposed research is to develop and test a prototype of an innovative and simple detector technique to identify moderate energy (a few MeV) positrons in space. Positron measurements at such energies have never been made in space. Measurement of the Galactic cosmic ray (GCR) positron fraction at low energies will provide new information about the transport and modulation of particles in the Local Interstellar Medium (LISM) and the Heliosphere. Also, positrons are unique among observable stable high energy particles since they are formed only as secondaries from high energy charged particle interactions in the Solar atmosphere during Solar particle events (SPEs). Positron measurements of this type will open a new channel for the study of Solar particle events which could address issues such as the determination of plasma and magnetic field parameters during high energy particle acceleration at the Sun, time evolution of Solar flare processes, and magnetic connectivity between acceleration sites and the interplanetary medium.</p> <p> Our detector scheme, the Positron Identification by Coincident Annihilation Photons (PICAP) technique, is based upon simple, reliable, well-proven and robust detectors. PICAP was inspired by the participation of the P.I. in a measurement of the &beta;+ half-life of 54Mn (for cosmic-ray chronometry) at Argonne National Laboratory using a similar technique [Wuosmaa et al. 1998]. The proposed project will develop and build a prototype PICAP instrument and expose it to negatrons and positrons at Jefferson Laboratory to demonstrate detection efficiencies and&mdash;equally important&mdash;PICAP&#39;s efficiency in discriminating against negatrons as false positrons. The prototype will also be exposed to protons at Indiana University Cyclotron Facility to demonstrate PICAP&#39;s efficiency in rejecting protons as false electrons. The goal is a proven detector system that, in a stand-alone instrument or, more likely, as part of a charged particle instrument/suite, can measure the energetic particle population at moderate energies (1-100&#39;s of MeV/nucleon), and can simultaneously measure the electron flux and positron fraction at previously unexplored energies. An instrument incorporating PICAP would be particularly attractive as to cost, mass, power and telemetry requirements, making it well suited to a variety of space missions in contrast to more complex and massive magnetic spectrometer techniques.</p> <p> The new addition to previous charged particle instrument designs is the additional capability to precisely measure the positron fraction. We propose to build a PICAP prototype, proving the positron detection capability, and optimized for the identification of 5-10 MeV positrons. A PICAP instrument may easily be tailored to measure other energies, depending upon specific science goals. A PICAP capability could be easily incorporated into a standard charged particle instrument designed to measure all moderate energy charged particles in space. &nbsp;</p> <p> N/A</p>