THE PREPARATION AND CHARACTERIZATION OF (LIF)-LI-6 AND B-10 REFERENCE DEPOSITS FOR THE MEASUREMENT OF THE NEUTRON LIFETIME

In beam experiments, the achievement of an accurate neutron lifetime measurements depends heavily on the use of well characterised boron and/or lithium reference deposits to assess the neutron density. Sets of (LiF)-Li-6 and B-10 reference deposits on silicon wafers were prepared by vacuum deposition using planetary rotating substrate holders. The uniformity of deposition was investigated using visible light spectrophotometry and accurate dimensional characterisation was carried out on the basis of travelling microscope and Talistep measurements. The results obtained agreed well with theoretical calculations based on the geometry of the evaporation system. The deposits prepared in successive evaporation runs were then characterised by neutron induced charged particle measurements, calibrated by isotope dilution mass spectrometry. Li-6 and B-10 surface densities are certified with accuracies of 0.35-0.50% and 0.30-0.41%, respectively. An intercomparison of the Li-6 and B-10 calibrations confirms the consistency of the measurements.