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 H2
17O or
H2
18O versus H2
natO, 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 possibilites for measuring the
partial structure factors of oxygen-containing compounds, such as water.
