Can solar 6Li abundance really be explained by Galactic cosmic rays?

Abstract

Cosmic-ray interactions are the only known source of the rare isotope 6Li. The standard picture is that the observed solar 6Li is produced by galactic cosmic rays accelerated in supernova remnants. Thus lithium-6 is a unique probe of the local Galactic (hadronic) cosmic-ray history. On the other hand, extragalactic gamma-ray background is a measure of cosmic-ray fluence but for the average star-forming galaxy. Using the connection between production of lithium and hadronic gamma-rays in cosmic-ray interactions we tested this assumption and came to a surprising andalarming result: extragalactic gammaray background allows for only ∼ 50% of solar lithium-6 abundance to be produced by Galactic Cosmic Rays. Although extreme assumptions yield a consistent picture, more realistic ones indicate that solar 6Li cannot be produced by standard GCRs alone without overproducing the hadronic gamma rays.