Experimental charge fractions in helium beams emerging from solids

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Abstract
The neutral fraction Phi 0 alpha and the fraction with unit charge Phi 1 alpha produced when 6-24 meV helium beams emerge from C, Al, Ni, Ag and Au thin targets are reported. The velocity nu 1 on emerging from the target ranges from 7.7 to 15.5 in atomic units of nu 0 approximately=2.18*108cms-1. Phi 0 alpha varies from about 10-5 to 10-9 and Phi 1 alpha from about 10-2 to 10-4. Both clearly depend on the atomic number Z2 of the material; Phi 0 alpha decreases approximately as nu 1-n with n varying between n approximately=12 for carbon (Z2=6) and n approximately=10 for gold (Z2=79), Phi 1 alpha decreases as nu 1-n with n' varying between n' approximately=6 for carbon and n' approximately=5 for gold. These results are compared with theoretical estimations using capture and cross sections by Bohr (1945) and Brinkman-Kramers (1930).