title: Similarity treatment of phase effects in stopping power of low energy heavy charged particles.
abstract: Bragg's additivity rule is the basis for calculating stopping powers of compounds from data on their constituent elements. Major assumptions in applying it are that chemical binding and the physical state of the stopping material have negligible influence on the slowing down process. The fragmentary and, at times conflicting evidence for phase effects for low energy heavy charged particles is summarised. A detailed survey of published stopping powers has been made and the information grouped according to target medium and phase. Each group has been fitted to universal curves of Lindhard type with the object of separating phase contributions to stopping. Least square fits have been made to each set of data. From these a quantitative measure of the effect is obtained and presented as stopping power ratios (vapour/condensed phase). From the experimental evidence available, it is concluded that phase effects do occur, decreasing the stopping power in solids and liquids as compared to the corresponding vapours, and are thought to be due largely to changes in electronic excitation levels as the phase is changed, combined with a physical-state dependence of the effective ion change at low energies. Magnitudes of the stopping power ratio deviate from unity by up to approximately 25%, but have significant associated errors, pointing to need for more accurate stopping power measurements.
mesh_terms: D000512:Alpha Particles; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D005740:Gases; D008956:Models, Chemical; D011522:Protons; D013329:Structure-Activity Relationship; D013696:Temperature
chemical_list: D005740:Gases; D011522:Protons