ELECTRONIC STOPPING IN A HE-H-2 MIXTURE SUBSTANTIALLY EXCEEDS BRAGGS RULE VALUE

We measured the energy loss of 8-keV deuterons in mixtures of He and H -2 gases using a rime-of-flight technique. According to Bragg's rule t he stopping cross section epsilon of a mixture of nonreacting gases sh ould be the weighted average of the stopping cross sections of its con stituents. Experimentally we find epsilon to exceed the Bragg value by more than 50%. This can be traced to large differences in the electro n capture and electron loss cross sections of He and H-2, respectively , that strongly enhance energy losses due to charge-changing collision s.