LITHIUM, BORON AND BERYLLIUM IN VOLCANIC GLASSES AND MINERALS STUDIEDBY NUCLEAR MICROPROBE

The detection of lithium, boron and beryllium was performed using a nu clear microprobe. The gamma-emission yields have been measured for the most favourable nuclear reactions: Li-7(alpha, alpha'gamma)Li-7, Li-7 (p, p'gamma)Li-7, B-10(p, alpha gamma)Be-7 and Li-7(p, n gamma)Be-7. T he possible interferences and the minimum detection limits (MDL) are p resented, at different energies and for a total integrated charge of 1 mu C Lithium and boron, studied by the reactions (p, p'gamma) and (p, alpha), respectively, have been determined in silicated glasses, as t race elements and on the scale of few micrometers. In the case of bery llium, using the Be-9(p, alpha gamma)Li-6 reaction, the MDL is calcula ted to be 1100 ppm for beryllium. This element has not been further st udied in our glass samples. PIGE (Proton Induced Gamma-ray Emission) a llows the simultaneous measurement of lithium, fluorine and sodium. St andardization curves were made for lithium and boron on the basis of n atural and synthetic glasses and minerals. Our results point out high baron contents in rhyolitic obsidians from Eolian Islands (Italy), com pared with other rhyolites. Concentrations in lithium, fluorine and ba ron were determined, for the first time, in glass inclusions trapped w ithin primitive minerals of the 1906 eruption of Vesuvius (Italy).