An instrument, the Caltech High Energy Isotope
Spectrometer Telescope (HEIST), has been developed to
measure isotopic abundances of cosmic ray nuclei in the
charge range 3 ≤ Z ≤ 28 and the energy range between 30 and
800 MeV/nuc by employing an energy loss -- residual energy
technique. Measurements of particle trajectories and
energy losses are made using a multiwire proportional
counter hodoscope and a stack of CsI(TI) crystal
scintillators, respectively. A detailed analysis has been
made of the mass resolution capabilities of this
instrument.
Landau fluctuations set a fundamental limit on the
attainable mass resolution, which for this instrument
ranges between ~.07 AMU for z~3 and ~.2 AMU for z~2b.
Contributions to the mass resolution due to uncertainties
in measuring the path-length and energy losses of the
detected particles are shown to degrade the overall mass
resolution to between ~.1 AMU (z~3) and ~.3 AMU
(z~2b).
A formalism, based on the leaky box model of cosmic
ray propagation, is developed for obtaining isotopic
abundance ratios at the cosmic ray sources from abundances
measured in local interstellar space for elements having
three or more stable isotopes, one of which is believed to
be absent at the cosmic ray sources. This purely
secondary isotope is used as a tracer of secondary
production during propagation. This technique is
illustrated for the isotopes of the elements O, Ne, S, Ar
and Ca.
The uncertainties in the derived source ratios due to
errors in fragmentation and total inelastic cross
sections, in observed spectral shapes, and in measured
abundances are evaluated. It is shown that the dominant
sources of uncertainty are uncorrelated errors in the
fragmentation cross sections and statistical uncertainties
in measuring local interstellar abundances.
These results are applied to estimate the extent to
which uncertainties must be reduced in order to
distinguish between cosmic ray production in a solar-like
environment and in various environments with greater
neutron enrichments.