A NEW MEASUREMENT OF THE FLUX OF THE LIGHT COSMIC-RAY NUCLEI AT HIGH-ENERGIES

A new cosmic-ray detector utilizing a ring-imaging Cerenkov counter to determine the energy of light cosmic-ray nuclei was flown on a high-altitude balloon from Fort Sumner, NM, in 1991 September. We describe the design and performance of this instrument and discuss the data analysis procedures. The measurement provides a new determination of the absolute flux and differential energy spectrum of the primary cosmic-ray species helium between 40 and 320 GeV nucleon-1. The experiment also yields the spectra of carbon and oxygen and some information on the intensities of the secondary nuclei Li, Be, and B. A comparison between our results and previous measurements of heavier nuclei (Z greater-than-or-equal-to 4) from HEAO 3 and Spacelab 2 indicates good consistency between these measurements. The data set is compared with the results of a leaky box propagation model. We find good agreement with this model if the abundance of helium relative to oxygen at the source is taken to be 25 +/- 6 and if the source spectrum is given by a power law in energy proportional to E-2.15.