  Reaction cross sections of 169Tm(alpha,gamma)173Lu and 169Tm(alpha,n)172Lu
have been measured in the energy range 12.6<=E_alpha<=17.5 MeV and
11.5<=E_alpha<=17.5 MeV, respectively, using the recently introduced method of
combining activation with X-ray counting. Improved shielding allowed to measure
the (alpha,gamma) to lower energy than previously possible. The combination of
(alpha,gamma) and (alpha,n) data made it possible to study the energy
dependence of the alpha width. While absolute value and energy dependence are
perfectly reproduced by theory at energies above 14 MeV, the observed change in
energy dependence at energies below 14 MeV requires a modification of the
predicted alpha width. Using an effective, energy-dependent, local optical
alpha+nucleus potential it is possible to reproduce the data but the
astrophysical rate is still not well constrained at gamma-process temperatures.
The additional uncertainty stemming from a possible modification of the
compound formation cross section is discussed. Including the remaining
uncertainties, the recommended range of astrophysical reaction rate values at 2
GK is higher than the previously used values by factors of 2-37.
