The Elemental Composition of High-Energy Cosmic Rays: Measurements with TRACER

Understand

TRACER ('Transition Radiation Array for Cosmic Energetic Radiation') is a balloon borne instrument that has been developed to directly measure the composition and energy spectra of individual heavy elements up to 10^15 eV per particle.

• TRACER achieves a large geometric factor (5 m^2 sr) through the use of a Transition Radiation Detector utilizing arrays of single wire proportional tubes.
• TRACER has measured the energy spectra of the elements O, Ne, Mg, Si, S, Ar, Ca, and Fe.
• The energy spectra reach energies in excess of 10^14 eV per particle and exhibit nearly the same spectral index (2.65 +/- 0.05) for all elements.