Anomalous energy losses for light projectiles traversing a polyvinylformyl resin

摘要

Measurements of the stopping powers of the polyvinylformyl resin known as formvar for 0.67-1.75 MeV protons, 1.19-3.02 MeV alpha particles, and 3.9-10.4 MeV Li-7 ions have been analyzed in terms of modified Bethe-Bloch theory for the purpose of extracting values of the dominant parameters of the formalism employed. These parameters are the target mean excitation energy and the Barkas-effect parameter, plus a single effective-charge parameter to characterize the interactions of He-4 and Li-7 projectiles with the target. Whereas results for the Barkas-effect parameter agreed well with the expected value of 1.4 +/- 0.1, results for the mean excitation energy lay about 20% below the value of 71.9 eV based on the assumption of linear additivity of stopping effects. Speculation as to the source of this difference is offered. (C) 2001 John Wiley & Sons, Inc. [References: 37]