COSMIC-RAY REENTRANT ELECTRON ALBEDO - HIGH-ENERGY ANTIMATTER TELESCOPE BALLOON MEASUREMENTS FROM FORT-SUMNER, NEW-MEXICO

The High-Energy Antimatter Telescope (HEAT) balloon cosmic ray detecto r flew from Fort Sumner, New Mexico on May 3-5, 1994. The instrument m easured electron and positron abundances and spectra from similar to 1 to 100 GeV at a vertical geomagnetic cutoff rigidity that varied betw een 4.0 and 4.5 GV. The intensities of electrons and positrons have be en measured as a function of atmospheric depth between 3.8 and 7.4 g c m(-2) of overburden. At magnetic rigidities below cutoff, the intensit y of downward moving e(+/-) consists of secondary (spallogenic) partic les and the reentrant (or return) albedo. We determine the contributio n of the reentrant electron albedo and compare it with earlier measure ments and limits at similar geomagnetic cutoff levels. In the range of 1.0-2.4 GeV, the reentrant albedo component amounts to 40% of the tot al electron intensity observed.