Optical absorption of isotopically enriched Li2B4O7 single crystals irradiated by thermal neutrons

Induced absorption spectra in the range 200-900 nm at 77 and 290 K for Li2B4O7 single crystals, isotopically Li and B enriched are presented after irradiation of these crystals by thermal neutrons with fluence 1.8x1016 cm-2. The dependence of induced absorption spectra on the isotope composition was revealed: for 6Li210B4O7 and 7Li210B4O7 crystals intensive band in the region of 280-294 nm was observed. Under substitution of 7Li isotope by 6Li in the lithium tetraborate lattice no changes in the absorption spectra were observed. The nuclear reaction 10B(n,α)7Li is proposed to be the main mechanism of formation of the radiation defects