  New measurements of the neutron-neutron quasifree scattering cross section in
neutron-deuteron breakup at an incident neutron energy of 10.0 MeV are
reported. The experiment setup was optimized to evaluate the technique for
determining the integrated beam-target luminosity in neutron-neutron
coincidence cross-section measurements in neutron-deuteron breakup. The
measurements were carried out with a systematic uncertainty of $\pm 5.6 \%$.
Our data are in agreement with theoretical calculations performed using the
CD-Bonn nucleon-nucleon potential in the Faddeev formalism. The measured
integrated cross section over the quasifree peak is $20.5 \pm 0.5 \text{(stat)}
\pm 1.1 \text{(sys)}$ mb/sr$^2$ in comparison with the theory prediction of
20.1 mb/sr$^{2}$. These results validate our technique for determining the
beam-target luminosity in neutron-deuteron breakup measurements.
