Concepts, Problems, & Opportunities for use of Annihilation Energy:

An Annotated Briefing on Near-Term RDT&E to Assess Feasibility

RAND Note N-2302-AF/RC

B. W. Augenstein

COMPARISON OF BEAM EFFECTIVENESS

(IN ALUMINUM)

An internal memorandum from LANL⁵ has presented a comparison ofmatter and antimatter beams based on a simplified model which includesenergy deposition estimates for primary beam slowdown and, for theantimatter beam, the pion contribution--assuming all annihilation pionsescape the annihilating nucleus. A suitably recast version of theseestimates is shown on the chart (P_LANL, _LANL). The estimates do notconsider any intranuclear effects.

We have attempted estimates on an effectively comparable simplifiedbasis of the intranuclear effect (for aluminum; these effects increaserelatively for heavier materials). The net result is shown on the chart_RAND The energy deposition cited is appropriate to the regionmarked on the previous chart. In some cases the deexcitation phenomena can be of special interest.

This estimated effect of intranuclear phenomena is significant andimportant as reflecting more closely the actual physics of the targetinteraction. The estimates are uniformly approximations which in ourview warrant improved calculations.

Those readers who wish a convenient and careful introduction to thephysics and computational aspects of intranuclear absorption areadvised to read first the leading paper in our Bibliography, by Cloveret al. at LANL.

The chart shows the averaged energy deposition per particleresulting from the very simple model used. From this the particle fluxrequired to obtain a given level of macroscopic energy deposition (e.g.,in joules/gram) is calculable. The model can be improved in realismsomewhat by using the actual form of the energy deposition, which e.g.,gives the usual pronounced increase in deposited energy near the end-of-path.This Bragg effect can typically increase the average energydeposition in the last 1/10 of the path to about 3 times the overallaverage deposition, and becomes relatively more important to considerwhen one seeks very large energy depositions.