Recent results in stopping power for positive ions, and some critical comments

An overview is given of developments in the field of stopping power during the last few years, with particular emphasis on cases that seem to require further work. We discuss experimental results showing that stopping power for low energy protons, in metals and insulators, is not necessarily proportional to velocity. We mention that there is no discrepancy between the mean ionization potential derived from optical data or from stopping power. The problem of the stopping power of liquid water is discussed, considering both experiment and theory, and we find that recent experimental results and one of the theories are apparently too low. We discuss various types of theories for stopping power. We stress that in analyzing bulk backscattering spectra for stopping power, a low energy limit of validity must be stated. Using statistical analysis of experimental data for heavy ions in elemental solids, we find that the ATIMA and SRIM programs and the Hubert table are best in different regions of specific energy.