Results on 7Li solar axions

The axion is a hypothetical particle which was proposed to solve the so-called problem of CP violation in strong interactions. If it exists, Sun could be an intensive source of axions. Energy spectrum of Solar axions would consists of the continuous part generated via the Primakoff effect, and quasi-monochromatic lines related with deexcitation of excited levels of nuclides present in Sun through magnetic nuclear transitions. These levels can be thermally excited because of high temperature in the solar core, or can be populated in nuclear reactions. In a deexcitation process, axions could be emitted instead of γ quanta with some probability which is related to the axion mass.

M1 transitions from the first excited level of 7Li (Eexc = 477.6 keV) in solar core also could be source of quasi-monochromatic axions. This 7Li* level is populated in pp chain of nuclear reactions in Sun when 7Be nucleus, produced through the 3He + α → 7Be + γ reaction, decays to 7Li. The 477.6 keV level of 7Li is occupied with 10.5% probability. Coming to Earth, these axions can be resonantly captured by 7Li nuclei. In the subsequent deexcitation process, γís of 477.6 keV will be emitted, and, therefore, the possible presence of such axions can be singled out by the presence of the characteristic peak in the energy distribution of a suitable detector placed close to or containing the 7Li sample.