The Isotopic Ratios of Helium, Lithium, Beryllium, and Boron in Cosmic Rays from 100-1800 Mev/nucleon.

The SMILI-2 (Superconducting Magnet Instrument for Light Isotopes) balloon-borne instrument package consisted of a two-coil superconducting magnet that provided the magnetic field needed for isotopic separation, 16 planes of drift tubes for particle tracking, a scintillator system for determining charge and time-of-flight, and a re-designed Cerenkov detector for measuring the highest particle velocities. The intermediate energy range investigated is above current satellite measurements and below planned space station experiments. The ^3He/^4 He isotopic ratio results support the original results of the SMILI-1 experiment and extend the energy range up to 1800 MeV/nucleon. Li, Be, and B isotopes are produced by fragmentation of heavier cosmic rays on interstellar material. The implications of the isotopic fractions of ^6Li/Li, ^7Be/Be, and ¹⁰B/B for cosmic ray source abundances and propagation models are discussed. In addition, estimates of the average interstellar density traversed by cosmic rays and the cosmic ray age are made based on the relative abundance of radioactive ¹⁰Be, whose half-life is similar to the average travel time of cosmic rays in the Galaxy.