FNWI --- IMAPP Department of Astrophysics
Radboud University > Faculty of Science > Department of Astrophysics


TRACER is a transition radiation detector, developed at the University of Chicago to measure individual element spectra of heavy cosmic-ray nuclei (oxygen to iron) in the energy range from 10 GeV to 100 TeV.

TRACER attached to the launch vehicle.  The TRACER detector unwrapped.

The big question in cosmic-ray physics is still open: What are the cosmic-ray sources and their properties? In order to be able to investigate the sources, the propagation of cosmic rays through the Galaxy must be understood, since it modifies the source spectra until they can be observed at the Earth. In a simple propagation model a cosmic-ray particle may reach the Earth, may escape the Galaxy, or may spallate into a lighter, secondary nucleus. The faster the escape from the Galaxy takes place, the fewer secondary nuclei are produced. Therefore, information on the propagation of Galactic cosmic rays can be inferred from the abundance ratio of secondary to primary cosmic-ray elements, like the boron-to-carbon ratio. Measuring this ratio poses formidable experimental challenges as the observations have to be conducted above the atmosphere and large exposure is needed to reach high energies. The TRACER detector was designed to achieve this measurement. It is currently the largest balloon-borne detector and capable of detecting cosmic rays well into the TeV/amu energy region with single element resolution.

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