The cosmic-ray 3He/4He ratio from 100 to 1600 MeV amu-1

J. J. Beatty, Washington University in St. Louis
D. J. Ficenec, Washington University in St. Louis
S. Tobias, Washington University in St. Louis
J. W. Mitchell, Universities Space Research Association
S. Mckee, University of Michigan, Ann Arbor
S. Nutter, University of Michigan, Ann Arbor
G. Tarlé, University of Michigan, Ann Arbor
A. Tomasch, University of Michigan, Ann Arbor
J. Clem, Louisiana State University
T. G. Guzik, Louisiana State University
M. Lijowski, Louisiana State University
J. P. Wefel, Louisiana State University
C. R. Bower, Indiana University Bloomington
R. M. Heinz, Indiana University Bloomington
S. L. Mufson, Indiana University Bloomington
J. Musser, Indiana University Bloomington
J. J. Pitts, Indiana University Bloomington
G. M. Spiczak, Indiana University Bloomington
S. P. Ahlen, Boston University
B. Zhou, Boston University


The Superconducting Magnet Instrument for Light Isotopes (SMILI) flew for 19 hours on 1989 September 1 with a residual overburden of 5 g cm-2. It measured the charge, rigidity, and velocity of 30,000 cosmic-ray helium nuclei, with velocity determined by time-of-flight and Cerenkov techniques. Using these data, the flux and isotopic composition of helium as a function of energy were determined. The observed isotopic composition is consistent with that expected from interstellar propagation models inferred from the secondaries of CNO, in contrast to earlier observations which indicated an overabundance of 3He. We discuss constraints that this result places on cosmic-ray transport and solar modulation models.