Mean excitation energy of polystyrene extracted from proton-stopping-power measurements

The measured stopping power of polystyrene for 2.2- to 5.9-MeV protons has been analyzed with the Bloch projectile-z/sup 4/ correction term and a modified low-velocity projectile-z/sup 3/ term included in the Bethe-Bloch formula. When the full-strength Walske K-shell correction was utilized, the mean excitation energy corresponding to the best fit of the measurements was (71.1 +- 1.8) eV. This result was obtained for a value of the free parameter of the low-velocity projectile-z/sup 3/ effect formalism of 1.90 +- 0.05, whether or not a Walske L-shell correction was included.