University of Minnesota
School of Physics & Astronomy


Insights into the galactic cosmic-ray source from the TIGER experiment


by J.T. Link, L.M Barbier, W.R. Binns, E.R. Christian, J.R. Cummings,
S. Geier, M.H. Israel, K. Lodders, R.A. Mewaldt, J.W. Mitchell, G.A. de Nolfo, B.F. Rauch, S.M. Schindler, L.M. Scott, R.E. Streitmatter, E.C. Stone, C.J. Waddington, and M.E. Wiedenbeck

We report results from 50 days of data
accumulated in two Antarctic flights of the Trans-
Iron Galactic Element Recorder (TIGER). With a
detector system composed of scintillators, Cherenkov
detectors, and scintillating optical fibers, TIGER has
a geometrical acceptance of 1.7 m2sr and a charge
resolution of 0.23 cu at Iron. TIGER has obtained
abundance measurements of some of the rare galactic
cosmic rays heavier than iron, including Zn, Ga, Ge,
Se, and Sr, as well as the more abundant lighter
elements (down to Si). The heavy elements have long
been recognized as important probes of the nature
of the galactic cosmic-ray source and accelerator.
After accounting for fragmentation of cosmic-ray
nuclei as they propagate through the Galaxy and the
atmosphere above the detector system, the TIGER
source abundances are consistent with a source that
is a mixture of about 20% ejecta from massive
stars and 80% interstellar medium with solar system
composition. This result supports a model of cosmicray
origin in OB associations previously inferred
from ACE-CRIS data of more abundant lighter
elements. These TIGER data also support a cosmicray
acceleration model in which elements present
in interstellar grains are accelerated preferentially
compared with those found in interstellar gas.

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