A measurement of the local energy deposition by antiprotons coming to rest in tissue-like material.

The measurement of the energy deposited in tissue-equivalent plastic as a beam of low-energy antiprotons slows down is described. The resulting depth-dose curve is presented and compared with that of protons measured under similar conditions. These curves indicate that the ratio of the dose in the antiproton stopping peak to that in the plateau region is about twice that found for protons. Analysis of the data shows that out of the 2 GeV available in an antiproton annihilation, on average less than 30 MeV is deposited close to the site of the interaction. This leads to the conclusion that antiprotons are unlikely to offer any marked advantage over other radiations for radiotherapeutic applications of the future.