The Ulysses High Energy Telescope (HET) allows for a study of Galactic
cosmic-ray manganese because of the telescope's excellent mass resolu
tion and large collecting area. The manganese isotopes in the cosmic r
ays provide a means of studying the parameters of the cosmic-ray propa
gation in the Galaxy. Each of the isotopes probes a separate aspect of
the propagation model. Mn-53, 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 Mn-53, but sen
sitivity to this is limited. The isotope Mn-54 decays in the laborator
y with tau(1/2) = 312 days by electron capture, but in the cosmic rays
, it has a beta(-) decay mode with an unmeasured partial half-life. Fr
om 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. Thi
s measurement raises the lower limit on the Mn-54 beta(-) partial half
-life by a factor of similar to 3. The iron-group escape time from the
Galaxy, even if the iron-group cosmic rays do not propagate as the lo
wer charge cosmic rays, is found to be similar to 18 tau beta(-). Fina
lly, the stable Mn-55 is found to have a source abundance, relative to
iron, consistent with a solar system abundance at the source.