A measurement of the absolute energy spectra of galactic cosmic rays during the 1976-77 solar minimum

An instrument designed to measure elemental cosmic ray abundances from boron to nickel in the energy region 0.5-2.0 GeV nucl-1 was flown on a high altitude balloon from Sioux Falls, South Dakota, on 30 September through 1 October 1976 at an average atmospheric depth of ∼5 g cm-2. Differential energy spectra of B, C, N, O, Ne, Mg, Si and Fe, extrapolated to the top of the atmosphere, were measured. The float altitude exposure of 17 h ended near Alpena, Michigan. The flight trajectory maintained a north easterly heading out of Sioux Falls traversing the upper mid-west region between 84o and 97o west longitude while remaining between 43.5o and 45o north latitude. The maximum vertical cut-off for this flight path was 1.77 GV or 0.35 GeV nucl-1. (author)