Detection of lithium by thin plastic foils

Abstract

To solve many present-day problems in geology, metallurgy and other fields of science and technology, it is often necessary to obtain information on the spatial distribution and concentration of an element. The low atomic number of lithium makes it difficult to study how this element is accommodated in the microstructure. However, the track-etch method, based on recording alpha particles formed in the (n, (u) reaction by thin plastic foils, does have the necessary sensitivity and resolution1’2. Alpha particles liberated by the ‘jLi (n, cx) 3H reaction have a short range. Thus only those originating within a few molecular layers of the specimen surface are capable of shallow penetration into the detector. For microscopy the latent alpha tracks on the detector foil are made visible by etching the foil in a hot alkali solution. If the sample contains both lithium and boron, the detector foil shows the sum of alpha particles from the ‘Li (n, o) 3H and i”B (n, cr) ‘Li reactions. We are at present developing a method of determining the distribution of lithium whilst eliminating interference from the boron, even when the lithium concentration is lower than that of boron3. The aim of this study was to consider the possibilities for determining rather high (7-30s) lithium concentrations in some mineral and glass samples. The procedure for detecting a very small amount of lithium (1 ppm or more) with the track-etch method will be reported later4.