Electronic stopping in a He-H2 mixture substantially exceeds Bragg's rule value.

Abstract

We measured the energy loss of 8 keV deuterons in mixtures of He and H{sub 2} gases using a time-of-flight technique. According to Bragg{close_quote}s rule the stopping cross section {var_epsilon} of a mixture of nonreacting gases should be the weighted average of the stopping cross sections of its constituents. Experimentally we find {var_epsilon} to exceed the Bragg value by more than 50{percent}. This can be traced to large differences in the electron capture and electron loss cross sections of He and H{sub 2}, respectively, that strongly enhance energy losses due to charge-changing collisions. {copyright} {ital 1996 The American Physical Society.}