EFFECTS OF SAMPLE PREPARATION ON THE STOPPING POWERS OF HAVAR FOR PROTONS AND ALPHA-PARTICLES

The stopping powers of Havar for 0.5-2.4 MeV protons and 1.2-1.8 MeV a lpha 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 u sed in order to learn if stopping power might be influenced by type of target foil preparation. The results indicated no such influence, sin ce all measurements were mutually consistent. Moreover, these data wer e thoroughly amenable to analysis with modified Bethe-Bloch theory, wh ich yielded generally plausible values of the parameters appearing in the modified Bethe-Bloch formula. Recommended values of these paramete rs are I=299.3+/-3.3 eV for the mean excitation energy, and b=1.33+/-0 .04 with xi=1.0 for the two Barkas-effect parameters.