The stopping powers of aluminiun and tantalum for 5–13.5 MeV protons and deuterons and 8–20 MeV 3He and 4He have been measured. At identical velocities, the ratio between the stopping powers for the double-charged and the single-charged ions is systematically higher than the factor four predicted by the Bethe formula. The deviation is 2.6% in Ta and 1.3% in Al at velocities corresponding to Ep = 2.5 MeV. The relative correction is roughly proportional to E−1.
Nuclear Physics, Section a, 1969, Vol 125, Issue 1, p. 171-175