Antiproton stopping power in He in the energy range 1-900 keV and the Barkas effect.

The anti-p stopping power in helium from 1 keV kinetic energy is evaluated. Contrary to the effect observed around and below the maximum, Obelix data indicate a anti-p stopping power higher than that for proton, the difference being of the order of 15\ub15% at 48 700 keV. The result contributes to assert the fundamental difference between anti-p stoppings in the simplest gases (He, H2) and in solid targets below some MeV