▁of ▁the ▁Sun , ▁. ▁For ▁this ▁reason , ▁a ▁precise ▁measurement ▁of ▁the ▁bor on - 8 ▁neut r ino ▁flux ▁can ▁be ▁used ▁in ▁the ▁framework ▁of ▁the ▁standard ▁solar ▁model ▁as ▁a ▁measurement ▁of ▁the ▁temperature ▁of ▁the ▁core ▁of ▁the ▁Sun . ▁This ▁estimate ▁was ▁performed ▁by ▁F ior ent ini ▁and ▁Ric ci ▁after ▁the ▁first ▁S NO ▁results ▁were ▁published , ▁and ▁they ▁obtained ▁a ▁temperature ▁of ▁ ▁from ▁a ▁determined ▁neut r ino ▁flux ▁of ▁ 5 . 2 · 1 0 6 / cm 2 · s . ▁ ▁Lith ium ▁de ple tion ▁at ▁the ▁solar ▁surface ▁St ell ar ▁models ▁of ▁the ▁Sun ' s ▁evolution ▁predict ▁the ▁solar ▁surface ▁chemical ▁abund ance ▁pretty ▁well ▁except ▁for ▁l ith ium ▁( Li ). ▁The ▁surface ▁abund ance ▁of ▁Li ▁on ▁the ▁Sun ▁is ▁ 1 4 0 ▁times ▁less ▁than ▁the ▁prot os olar ▁value ▁( i . e . ▁the ▁prim ord ial ▁abund ance ▁at ▁the ▁Sun ' s ▁birth ), ▁yet ▁the ▁temperature ▁at ▁the ▁base ▁of ▁the ▁surface ▁con ve ct ive ▁zone ▁is ▁not ▁hot ▁enough ▁to ▁burn ▁– ▁and ▁hence ▁de ple te ▁– ▁Li . ▁This ▁is ▁known ▁as ▁the ▁solar ▁l ith ium ▁problem . ▁A ▁large ▁range ▁of ▁Li ▁abund ances ▁is ▁observed ▁in ▁solar - type ▁stars ▁of ▁the ▁same ▁age , ▁mass , ▁and ▁met all icity ▁as ▁the ▁Sun . ▁Observ ations ▁of ▁an ▁un bi ased ▁sample ▁of ▁stars ▁of