Effects of sample preparation on the stopping powers of Havar for protons and alpha particles.

Abstract

The stopping powers of Havar for 0.5--2.4 MeV protons and 1.2--1.8 MeV \ensuremath{\alpha} particles have been measured with uncertainties of a little more than 0.6% and slightly less than 0.6%, respectively. Havar foils with three different tempers---cold-rolled, annealed, and heat-treated---were used in order to learn if stopping power might be influenced by type of target foil preparation. The results indicated no such influence, since all measurements were mutually consistent. Moreover, these data were thoroughly amenable to analysis with modified Bethe-Bloch theory, which yielded generally plausible values of the parameters appearing in the modified Bethe-Bloch formula. Recommended values of these parameters are I=299.3\ifmmode\pm\else\textpm\fi{}3.3 eV for the mean excitation energy, and b=1.33\ifmmode\pm\else\textpm\fi{}0.04 with \ensuremath{\xi}=1.0 for the two Barkas-effect parameters.