STOPPING POWERS OF 200-3000 KEV HE-4 AND 550-1750 KEV H-1 IONS IN VYNS

Stopping powers for Vyns (vinylchloride-vinylacetate copolymer) were m easured both for He-4 ions in the range 200-3000 keV and for H-1 ions in the range 550-1750 keV using the transmission technique. A detector model is used for the energy calibration to improve the accuracy of t he stopping power curve for He-4 ions in the low energy region. The es timated uncertainty in the stopping power values is similar to 1.5% fo r He-4 ions and similar to 2% for H-1 ions. A comparison is made betwe en a parametrization of the present data and several parametrizations of the stopping power found in the literature. The stopping power valu es closest to the present experimental data for He-4 ions are obtained by adding elemental stopping powers using Bragg's rule. For this the experimental values for the C1 stopping power reported earlier should be used. The charge state scaling, sometimes used to take account for phase-state effects, is not appropriate for Vyns. For H-1 ions, the pa rametrization closest to our data is that of Janni from 1982.