An investigation into the use of the nuclear microprobe for examining distributions of boron isotopes

A technique has been developed to permit the distribution of boron isotopes in metal samples to be measured with the nuclear microprobe. Samples are irradiated with focussed beams of α-particles, and protons from the (α,p) reactions on both 10B are counted. Particle spectroscopy enables contributions from the two isotopes to be determined separately from the same spectrum and distributions can be followed by varying the position of the ion beam on the sample surface. To confirm the reliability of the measurement of protons from (α,p) reaction for determining 10B/11B ratios, the α-particle beam was scanned across a standard steel containing boron of known isotopic composition. 10B and 11B concentrations were measured and the isotopic ratio calculated. 30 measurement on one steel provided an isotopic ratio of of 0.247+-0.015 compared with a value of 0.248+-0.007 found by mass spectroscopy while 43 measurements on the second sample gave an isotopic ratio of 9.36+-1.68 compared with the mass spectroscopy figure of 9.25+-0.05. These results suggest that the (α,p) reaction provides a means of determining the isotopic ratios of boron. (T.G.)