Path-lengths and source spectra of cosmic-ray helium and heavy nuclei

Abstract

It is shown that assuming a source spectrum of the He nuclei of the form [Formula: see text] it is possible to explain accurately both the shape of the differential spectrum in the interval 40–1 000 MeV/nucleon and the ³He/(³He + ⁴He) ratios, and to determine the value of the residual solar modulation. This is not possible with other simple forms of source spectra. For medium nuclei[Formula: see text] it is found that a source spectrum of the above form can also explain both the observed Li/M ratios and the differential spectrum in the energy interval 100–1 000 MeV/nucleon using the same value of residual solar modulation. But there remains an excess flux of medium nuclei in the energy interval 40–100 MeV/nucleon to account for, so that it is necessary to consider a second source. Assuming that these nuclei traverse a very small amount of matter in space, the form of the second-source spectrum is obtained as [Formula: see text], the value of the index being the lower limit.