How does the composition of cosmic rays change with energy?
When we ask about composition, we are asking about what cosmic rays are made of. Are they protons, electrons, or something else? As discussed above, low energy cosmic rays consist of mainly protons and light nuclei. Measurements taken in a high altitude balloon, the Japanese-American Cooperative Emulsion Experiment (JACEE), show that as the cosmic ray energy increases, the proportion of heavier nuclei also increases. This suggests that as the energy reaches around 1015 eV, heavy nuclei become the dominant component. It is very difficult, however, for a satellite or balloon experiment like JACEE to study particles at these high energies. This is because the flux flux: the number of particles arriving per unit area per unit time.’);”> –> is very low, and the detector area that can be carried aboard a satellite is so small. A better alternative is to use a ground based detector to sample the energies from extensive air showers and infer the particle energies indirectly. The situation is
