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Proton and Helium 
The proton and helium energy spectra have been measured by PAMELA  in the energy range 1 GeV - 1 TeV and 1 GeV - 450 GeV, respectively, and are shown in Figure 1. The various periods of solar activity in which data have been collected from several experiments could explain the differences at energies lower than 30 GeV as due to different solar modulation effects.
A spectral hardening appears in the two slopes  at the highest energies explored, challenging the present paradigm of acceleration of cosmic rays by a single supernovae remnant. These sudden changes are more evident at 230 - 240 GV, as shown in the Figures 2  and Figure 4, where the data are plotted as a function of rigidity. They could be interpreted as an indication of different populations of cosmic ray sources, as novae stars and explosions in superbubbles.
The problem of the possible uniqueness of the index spectrum for all nuclei, including protons and helium, has been a debated issue from long time. The precise PAMELA data, shown in  Figure 3 as ratio of the proton to helium fluxes versus rigidity in order to cancel systematic instrumental effects, clearly evidence a difference between the proton and helium slopes, showing that the helium slope is harder than the proton one. The ratio exhibit a continuous and smooth decrease and it is well described by a power law down to 5 GV with a spectral index of 0.1.


PAMELA is also measuring 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 5  and Figure 6, respectively, together with proton and helium fluxes. The 2H/1H and 3He/4He ratios are reported in Figure 7  and Figure 8 , while the isotopic ratio 2H/4He is shown in Figure 9.


The propagation of cosmic rays inside our galaxy plays a fundamental role in shaping their injection spectra into those observed at Earth. One of the best tools to investigate this issue is the ratio of fluxes for secondary and primary species. The Boron-to-Carbon (B/C) ratio, in particular, is a sensitive probe to investigate propagation mechanisms. Boron and Carbon absolute fluxes and B/C ratio were measured by the PAMELA space experiment and are shown in Figure 10 and Figure 11 respectively. The results span the range 0.44-129 GeV/n in kinetic energy for the data taken in the period 2006 July to 2008 March.


Edited by Vincenzo Buttaro