Jay P. Norris

Search for time variations in 511 keV flux by ISEE-3 gamma-ray spectrometer

The ISEE‐3 gamma‐ray spectrometer has provided nearly continuous monitoring of the cosmic gamma‐ray background in the energy regime 125 keV to 6.5 MeV since launch of the satellite in August 1978. The data has been analyzed for possible variations in the cosmic 511 keV line flux. The detector is an unshielded, radiatively‐cooled, high‐purity germanium crystal with a sensitive volume 33 cm3. At energies ≳100 keV the detector has a field‐of‐view of ≳2π steradians which includes the galactic center. The detector resolution was degraded continuously by exposure to high‐energy charged particles in the interplanetary space enviroment; consequently, only the first 500 day sample of data is usable. Proton and electron flux rates available from a cosmic‐ray experiment aboard ISEE‐3 were used to eliminate all periods during which solar energetic particles contributed signficantly to our counting rate.. We are able to place upper limits on the variability of the cosmic 511 keV flux of <2.2×10−2 and <1.3×10−2 photons...