Abstract
The technique of neutron interferometry was used to measure the bound coherent neutron scattering length bcoh of the oxygen isotopes 17O and 18O. From the measured difference in optical path between two water samples, either H217O or H218O versus H2natO, where nat denotes the natural isotopic composition, we obtain bcoh,17O = 5.867(4) fm and bcoh,18O = 6.009(5) fm, based on the accurately known value of bcoh,natO = 5.805(4) fm which is equal to bcoh,16O within the experimental uncertainty. Our results for bcoh,17O and bcoh,18O differ appreciably from the standard tabulated values of 5.6(5) fm and 5.84(7) fm, respectively. In particular, our measured scattering-length contrast of 0.204(3) fm between 18O and natO is nearly a factor of 6 greater than the tabulated value, which renders feasible neutron diffraction experiments using 18O isotope substitution and thereby offers new possibilities for measuring the partial structure factors of oxygen-containing compounds, such as water.
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