Proton activation analysis for the determination of trace elements in high purity ZrF 4 used for the fabrication of low-loss optical fibres

Abstract

Fluoride glasses may be used in the future for the making of ultralow-loss optical fibres at 2.5 μm. Low absorption can only be achieved if the glasses contain ppb levels of some transition elements and of lanthanides. So the starting materials (ZrF 4, A1F 3, NaF, LaF 3 …) must be purified and controlled. At the present time, there is a lack of suitable standard analytical methods; we have therefore developed a method based on proton activation at 23 MeV. In this work we present analytical results for the determination of Fe and Ni in ZrF 4, at trace level. ZrF 4, as a powder, is irradiated for 2 h at 0.5 μA. After dissolution in HF, the matrix activity is eliminated by combining different radiochemical separations. The activity of the radioisotopes of interest, 56Co for Fe, 57Ni for Ni, is then determined by gamma-ray spectrometry.