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 1.8×10¹⁶ 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,)⁷Li is proposed to be the main mechanism of formation of the radiation defects.