Emulsion chamber observations of primary cosmic-ray electrons in the energy range 30--1000 GeV

A series of emulsion exposures, beginning in Japan in 1968 and continued in the U.S. since 1975, has yielded a total balloon-altitude exposure of 98,700 m2 sr s, nearly 10 times the exposure factor obtained by other experiments. The electron spectrum derived by combined data from all our chambers exposed from 1968 to 1976 is well represented by J/sub e/(E)=1.6 x 10-4(100 GeV/E)/sup 3.3plus-or-minus0.2/ /m2 sr s GeV in the energy range 30--1000 GeV. This result is in good agreement with our earlier results and with those of several other groups. We discuss our data in terms of several models of cosmic-ray propagation. Interpreted in terms of the energy-dependent leaky-box model, our electron spectrum results suggest a galactic electron residence time of 1.0(+2.0, -0.5) x 107 yr, which is consistent with the result from 10Be observations. Additional chambers current under analysis will allow us reliably to extend the spectrum beyond 1 TeV. We discuss the possibly that departures from smooth power-law behavior in the spectrum due to individual nearby sources will be observable in this energy range