Lithium, boron and beryllium in volcanic glasses and minerals studied by nuclear microprobe

Abstract

The detection of lithium, boron and beryllium was performed using a nuclear microprobe. The γ-emission yields have been measured for the most favourable nuclear reactions: 7Li(α, α′γ) 7Li, 7Li(p, p′γ) 7Li, 10B(p, αγ) 7Be and 7Li(p, nγ) 7Be. The possible interferences and the minimum detection limits (MDL) are presented, at different energies and for a total integrated charge of 1 μC. Lithium and boron, studied by the reactions (p, p′γ) and (p, α), respectively, have been determined in silicated glasses, as trace elements and on the scale of few micrometers. In the case of beryllium, using the 9Be(p, αγ) 6Li reaction, the MDL is calculated to be 1100 ppm for beryllium. This element has not been further studied in our glass samples. PIGE (Proton Induced Gamma-ray Emission) allows the simultaneous measurement of lithium, fluorine and sodium. Standardization curves were made for lithium and boron on the basis of natural and synthetic glasses and minerals. Our results point out high boron contents in rhyolitic obsidians from Eolian Islands (Italy), compared with other rhyolites. Concentrations in lithium, fluorine and boron were determined, for the first time, in glass inclusions trapped within primitive minerals of the 1906 eruption of Vesuvius (Italy).