Antiproton-Hydrogen Atom Annihilation.

Abstract

Abstract : For antiproton energies of several eV or less annihilation in matter occurs through atomic rearrangement processes in which the antiproton becomes bound to a nucleus prior to annihilation. Annihilation cross sections via rearrangement at such energies are much higher than for direct antiproton nucleon annihilation and are therefore of consequence to antiproton annihilation propulsion of space craft. Existing calculations of the antiproton-hydrogen atom rearrangement cross section are semiclassical and employ the Born Oppenheimer approximation. They also employ various arguments in regard to the behavior of the system when the Born Oppenheimer approximation breaks down at small antiproton-proton separations. These arguments indicate that rearrangement is essentially irreversible. In the present study, a detailed investigation was made of the antiproton-hydrogen atom system when the Born Oppenheimer approximation breaks down. The results of this study indicate that the previous arguments were approximately correct, but that there is a significant probability for rearrangement reversing prior to annihilation. This probability is estimated to be about 20%. This consequent reduction in annihilation cross section has little or no negative consequences for antiproton annihilation propulsion at the present time. However, because of the approximate nature of this result and because more accurate values will be required in the future, it is important to conduct an accurate, fully quantum mechanical calculation of antiproton-hydrogen atom rearrangement.