PAMELA has also measured the hydrogen and helium isotopes in cosmic rays. The combined effect of acceleration and propagation of cosmic rays in the Galaxy leads to a difference between the spectra at the source and those measured at Earth: secondary nuclei are produced by spallation in the interaction of primary nuclei with interstellar matter. Powerful tools to characterize the diffusion property of the interstellar matter and to test the propagation models are therefore the measurements of the abundances and energy spectra of secondary elements.
The isotopic composition was measured between 100 and 1100 MeV/n for Hydrogen and between 100 and 1400 MeV/n for Helium isotopes over the 23rd solar minimum from 2006 July to 2007 December. Proton and helium isotope absolute fluxes are shown in Figure 1 and Figure 2 (top), respectively, together with proton and helium fluxes. The 2H/1H and 3He/4He ratios are reported in Figure 1 and Figure 2 (bottom), respectively.
