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

Abstract 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 84° and 97° west longitude while remaining between 43.5° and 45° north latitude. The maximum vertical cut-off for this flight path was 1.77 GV or 0.35 GeV nucl -1 (Shea and Smart (1975), Report No. AFCRL-TR-75-0185, Air Force Cambridge Research Laboratories).