Stopping powers of Ta and Mo for MeV protons

Abstract

The stopping powers of Ta and Mo were measured respectively for protons of 4.5–20.0 MeV and 4.0–12.5 MeV, with an accuracy of ±0.3%. The results for Mo agree very well with the calculated values in ICRU Report 49. By analyzing the experimental results using the modified Bethe-Bloch formula including the Barkas correction, we deduced the mean excitation energy, the I value. In this analysis, we used the Barkas correction of Ashley, Ritchie and Brandt and Bonderup's and Bichsel's shell corrections for the shell correction. The I values, respectively obtained with the Bonderup and Bichsel shell corrections, were 685.1 ± 30.2 eV and 743.1 ± 24.8 eV for Ta and 420.3 ± 14.8 eV and 426.9 ± 13.4 eV for Mo. These two I values for Ta differ and the Bonderup shell correction does not fit the experimental data well. On the other hand, the I values for Mo are very similar and the Bonderup and Bichsel shell corrections both reproduce the experimental situation nearly equally well.