Measurements of the spectra and isotopic composition of cosmic ray helium and hydrogen nuclei from 120 to 235 MeV/nucleon

Differential energy spectra of primary cosmic ray H1, H2, He3, and He4 nuclei in the energy range 120-235 MeV per nucleon were measured on a balloon flight from Thompson, Manitoba in August 1973 during a time of relatively quiet interplanetary conditions. The detector was a Geiger tube hodoscope operated in conjunction with a double dE/dx vs. E scintillation counter with resolution sufficient to resolve the isotopes of hydrogen and helium at energies not resolved by typical satellite telescopes. The Geiger tube hodoscope provided information on path length inclination and penetration coordinates in each detector enabling corrections for path length variation and nonuniformities in detector response to be made for each event. The observed helium (He3 + He4) spectrum above 125 MeV/nucleon connects smoothly with the ''anomalous'' helium spectrum (characterized by a He4 excess) measured by satellites below 100 MeV/nucleon during the same time period. The observed average He3/(He3 + He4) ratio was found to be 0.105 +- 0.012 which is larger than the average value of approximately 0.06 measured by satellites below 100 MeV/nucleon indicating the anomaly does not extend into the energy range covered by this experiment. When corrected for solar modulation the abundance ratio of He3 to (He3 + He4) is consistent with the traversal of a mean thickness of interstellar gas of 4-6 gm/cm2 between cosmic ray sources and the local interstellar space. The small deuteron flux coupled with abundant production of secondaries in the overlying atmosphere made it possible to quote only upper limits for the deuteron spectrum. Proton spectra were also measured on two flights from Fort Churchill, Manitoba in late 1972 during a period of enhanced solar activity