Annihilation of Antiprotons in Heavy Nuclei.

A literature survey was conducted to find information relevant to the annihilation of a low energy sub MeV antiproton in a heavy nucleus. Such information is important to the use of nuclear fragments from the annihilation to heat a working fluid for space propulsion. The particular piece of information desired was the fraction of annihilation energy that becomes the kinetic energy of charged nuclear fragments emitted after annihilation. The experimental and theoretical information located was sufficient to allow calculation of that energy fraction. Its value is about 10 for nuclei as heavy as silicon or greater and 20 for very heavy nuclei when the energy of fission fragments is included. Both values are less than a fraction of annihilation energy 38 that becomes the kinetic energy of charged pions from the annihilation of an antiproton with a proton hydrogen nucleus. These values are relevant to the choice of a working fluid that absorbs a portion of the annihilation energy and forms the exhaust for a rocket powered by antiproton annihilation. Althouth it is easier to couple the energy of charged nuclear fragments to the working fluid, the higher energy fraction for the charged pions makes hydrogen more attractive as the working fluid. It is therefore important to investigate possible means for efficient transfer of the pion energy to the working fluid.