Evidence for a Forbush Type of Decrease in the Intensity of Heavy Nuclei of the Primary Cosmic Radiation

Abstract

In an emulsion stack flown on March 13, 1956 from Iowa, the flux of heavy nuclei with $Z\ensuremath{\ge}6$ in the primary cosmic radiation was measured as 15.8\ifmmode\pm\else\textpm\fi{}1.0 and 3.7\ifmmode\pm\else\textpm\fi{}0.6 particles/${\mathrm{m}}^{2}$ sec sr for particles of kinetic energy \ensuremath{\ge}0.23 and \ensuremath{\ge}1.55 Bev/nucleon, respectively. The measured flux of energy \ensuremath{\ge}1.55 Bev/nucleon was 57\ifmmode\pm\else\textpm\fi{}11% lower than the normal flux. It is shown that almost the entire part of the reduction must be attributed to a large Forbush decrease of the cosmic radiation that occurred at the same time. The exponent of the integral energy spectrum of heavy nuclei ($Z\ensuremath{\ge}6$) was measured as 1.78\ifmmode\pm\else\textpm\fi{}0.24 in the energy interval 0.23 to 9 Bev/nucleon. As this value is not significantly different from its normally measured value, it appears that the large reduction in the primary flux was not accompanied by any significant change in the energy spectrum.