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

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Abstract
It is shown that assuming a source spectrum of the He nuclei of the form 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 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 , the value of the index being the lower limit.
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