Excitation of 10-MeVH0Atoms in Neutral- and Charged-Particle Collisions

Abstract

Ten-MeV hydrogen atoms with a distribution of excited states were produced by collisional dissociation of 20-MeV $\mathrm{H}_2^{}{}_{}{}^{+}$ ions. The populations of the higher excited levels were removed by Lorentz ionization, and the levels were then repopulated by collisional excitation of the atoms in molecular or weakly ionized hydrogen targets. The populations of the levels $n=6\mathrm{} \mathrm{to} 9$ were determined by a second Lorentz ionization. For collisions with electrons and ions in hydrogen-plasma targets, cross sections for transitions from the levels $n=5,6\mathrm{}$ to $n^{\prime }=6,7,8,9\mathrm{}$, and upper limits for the transitions $n=1\mathrm{} or 4$ to $n^{\prime }=6\mathrm{} or 7$ have been obtained. These are compared with calculations in the first Born, Bethe, and impact-parameter approximations; good agreement is found for all transitions, although those with $\Delta n=2\mathrm{}$ are somewhat larger than calculated. For molecular-hydrogen targets, transitions are observed from the sum of all levels with $n\le 4,5,6$ to levels $n^{\prime }=6,7,8,\mathrm{and} 9$. Cross sections for the individual transitions from $n=5,6\mathrm{}$ to the levels $n^{\prime }=6,7,8,\mathrm{and} 9$ have been deduced from these results. These cross sections differ from those for charged-particle collisions in that they are smaller by about 3 orders of magnitude, and the ratios of cross sections with $\Delta n>\mathrm{}1\mathrm{}$ to those of $\Delta n=1\mathrm{}$ are larger than in the charged-particle case.