Propagation of Galactic Cosmic Rays: The Measurement of the Boron-to-Carbon Ratio of TRACER
by
Andreas Obermeier(Radboud Universiteit Nijmegen)
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Europe/Stockholm
FA32
FA32
Description
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 proparation 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. Here we present the results of the last long-duration balloon flight of TRACER, including a new measurement of the boron-to-carbon ratio up to 2 TeV/amu. We also present implications this measurement poses for cosmic-ray propagation and, subsequently, their sources.
