An instrument, the Caltech High Energy IsotopeSpectrometer Telescope (HEIST), has been developed tomeasure isotopic abundances of cosmic ray nuclei in thecharge range 3 ≤ Z ≤ 28 and the energy range between 30 and800 MeV/nuc by employing an energy loss -- residual energytechnique. Measurements of particle trajectories andenergy losses are made using a multiwire proportionalcounter hodoscope and a stack of CsI(TI) crystalscintillators, respectively. A detailed analysis has beenmade of the mass resolution capabilities of thisinstrument.
Landau fluctuations set a fundamental limit on theattainable mass resolution, which for this instrumentranges between ~.07 AMU for z~3 and ~.2 AMU for z~2b.Contributions to the mass resolution due to uncertaintiesin measuring the path-length and energy losses of thedetected particles are shown to degrade the overall massresolution to between ~.1 AMU (z~3) and ~.3 AMU(z~2b).
A formalism, based on the leaky box model of cosmicray propagation, is developed for obtaining isotopicabundance ratios at the cosmic ray sources from abundancesmeasured in local interstellar space for elements havingthree or more stable isotopes, one of which is believed tobe absent at the cosmic ray sources. This purelysecondary isotope is used as a tracer of secondaryproduction during propagation. This technique isillustrated for the isotopes of the elements O, Ne, S, Arand Ca.
The uncertainties in the derived source ratios due toerrors in fragmentation and total inelastic crosssections, in observed spectral shapes, and in measuredabundances are evaluated. It is shown that the dominantsources of uncertainty are uncorrelated errors in thefragmentation cross sections and statistical uncertaintiesin measuring local interstellar abundances.
These results are applied to estimate the extent towhich uncertainties must be reduced in order todistinguish between cosmic ray production in a solar-likeenvironment and in various environments with greaterneutron enrichments.
