Measurement of the coherent neutron scattering length of $sup 3$He by reflection from a quartz-liquid-helium interface

The real part of the bound-atom coherent neutron scattering length of $^{3}\mathrm{He}$ has been measured by comparing the reflectivities of quartz-liquid-$^{3}\mathrm{He}$ and quartz-liquid-$^{4}\mathrm{He}$ interfaces and has been found to have the value (6.1 \ifmmode\pm\else\textpm\fi{} 0.6) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}\phantom{\rule{0ex}{0ex}}13}$ cm.