The Spectrum of Galactic Electrons with Energies Between 10 and 900 GEV

A cosmic-ray electron detector has been designed which consists of a counter telescope with 1060 cm2 sterad geometry factor and a lead scintillator sandwich of about 19 radiation lengths thickness. In order to identify electron showers efficiently, multiple pulse-height analysis of many counters and time-of-flight techniques have been used. This instrument has been exposed during 1970 in three high-altitude balloon flights from Palestine, Texas. The data analysis is based on results from accelerator calibrations with electrons and pions at SLAC. Discrimination against a contamination of the electron data due to interacting protons has been achieved by statistical methods. The resulting differential energy spectrum of cosmic-ray electrons can be well described by a single power law with spectral index 2.66 i 0.1 up to energies around 250 GeV. Within the experimental uncertainty, no change in this spectral slope up to almost 1000 GeV can be detected. Some implications of these results are discussed. Subject heading: cosmic rays