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 detector flew from Fort Sumner, New Mexico on May 3-5, 1994. The instrument measured electron and positron abundances and spectra from similar to 1 to 100 GeV at a vertical geomagnetic cutoff rigidity that varied between 4.0 and 4.5 GV. The intensities of electrons and positrons have been measured as a function of atmospheric depth between 3.8 and 7.4 g cm(-2) of overburden. At magnetic rigidities below cutoff, the intensity of downward moving e(+/-) consists of secondary (spallogenic) particles and the reentrant (or return) albedo. We determine the contribution of the reentrant electron albedo and compare it with earlier measurements 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 total electron intensity observed.