Stopping Powers of S32, Cl35, Br79, and I127 Ions in Mylar

Abstract

Stopping powers of Mylar are presented for ${\mathrm{S}}^{32}$ ions of mean energy 15 to 95 MeV, ${\mathrm{Cl}}^{35}$ ions of 15 to 95 MeV, ${\mathrm{Br}}^{79}$ ions of 30 to 90 MeV, and ${\mathrm{I}}^{127}$ ions of 60 and 105 MeV. The heavy-ion beams were accelerated on the Rochester MP tandem Van de Graaff; energies were known to ±50 keV. The precision of energy-loss measurements was of the order of 2% with an estimated accuracy of ±8%. The experimentally determined stopping powers were used with the Bethe-Bloch equation and experimental proton stopping powers to calculate effective charges. The fractional effective charges for the ions investigated all fit a single smooth curve when compared with a reduced velocity variable; published values for ${\mathrm{O}}^{16}$-ion stopping powers in carbon and aluminum yielded effective charges which fit the same curve. The effective charges for ${\mathrm{S}}^{32}$, ${\mathrm{Br}}^{79}$, and ${\mathrm{I}}^{127}$ are compared with the experimental most probable charge states, and are found to be less than the experimental values in all cases. This variation at its greatest is found to be 67%.