MEASUREMENT OF THE BARKAS EFFECT USING MEV ANTIPROTONS AND PROTONS AND AN ACTIVE SILICON TARGET

The recently reported measurements of the Barkas effect are described in detail. The method, which infers the energy loss of the projectiles from the energy deposited in thin transmission silicon detectors, is tested by reproducing well-known stopping powers for protons and alpha particles. The antiproton stopping power of silicon is found to be 3-19% lower than for equivelocity protons over the energy range 3.0-0.538 MeV. The "Z13 contribution" to the stopping power, the Barkas term, is deduced by comparing the measured antiproton stopping power to that of protons. Finally, future experiments are briefly discussed. © 1990.