Galactic Cosmic-Ray Manganese: Ulysses High Energy Telescope Results

Abstract

The Ulysses High Energy Telescope (HET) allows for a study of Galactic cosmic-ray manganese because of the telescope's excellent mass resolution and large collecting area. The manganese isotopes in the cosmic rays provide a means of studying the parameters of the cosmic-ray propagation in the Galaxy. Each of the isotopes probes a separate aspect of the propagation model. ⁵³Mn, a long-lived electron capture species, measures the time between the nucleosynthesis and acceleration of the cosmic rays. There is no evidence found for a source of ⁵³Mn, but sensitivity to this is limited. The isotope ⁵⁴Mn decays in the laboratory with τ_1/2 = 312 days by electron capture, but in the cosmic rays, it has a β^- decay mode with an unmeasured partial half-life. From the HET data, this partial half-life is found to be near 1 Myr, if the iron-group cosmic rays propagate like the lighter cosmic rays. This measurement raises the lower limit on the ⁵⁴Mn β^- partial half-life by a factor of ~3. The iron-group escape time from the Galaxy, even if the iron-group cosmic rays do not propagate as the lower charge cosmic rays, is found to be ~18τ_β^-. Finally, the stable ⁵⁵Mn is found to have a source abundance, relative to iron, consistent with a solar system abundance at the source.

Submitted to the Department of Physics, University of Chicago, in partial fulfillment of the requirements for the Ph.D. degree.