  The TRACER instrument Transition Radiation Array for Cosmic Energetic
Radiation is designed to measure the individual energy spectra of cosmic-ray
nuclei in long-duration balloon flights The large geometric factor of TRACER 5
m 2 sr permits statistically significant measurements at particle energies well
beyond 10 14 eV TRACER identifies individual cosmic-ray nuclei with
single-element resolution and measures their energy over a very wide range from
about 0 5 to 10 000 GeV nucleon This is accomplished with a gas detector system
of 1600 single-wire proportional tubes and plastic fiber radiators that measure
specific ionization and transition radiation signals combined with plastic
scintillators and acrylic Cherenkov counters A two-week flight in Antarctica in
December 2003 has led to a measurement of the nuclear species oxygen to iron O
Ne Mg Si S Ar Ca and Fe up to about 3 000 GeV nucleon We shall present the
energy spectra and relative abundances for these elements and discuss the
implication of the results in the context of current models of acceleration and
propagation of galactic cosmic rays The instrument has been refurbished for a
second long-duration flight in the Northern hemisphere scheduled for summer
2006 For this flight the dynamic range of TRACER has been extended to permit
inclusion of the lighter elements B C and N in the measurement.
