Update on the direct n-n scattering experiment at the reactor YAGUAR

The first direct measurement of the $^{1}S_{0}$ neutron-neutron scattering experiment using the YAGUAR aperiodic reactor at the Russian Federal Nuclear Center $-$ All Russian Research Institute of Technical Physics has preliminary results. Thermal neutrons are scattered from a thermal neutron ``gas'' within the scattering chamber of the reactor and measured via time-of-flight. These initial results show an unexpectedly large thermal neutron background now understood to be from radiation-induced desorption within the scattering chamber. Analysis of the neutron time-of-flight spectra suggests neutron scattering from H$_2$ and possibly H$_2$O molecules. An experimental value for the desorption yield $\eta_{\gamma}$ of 0.02 molecules/gamma agrees with modeled results. Techniques to reduce the effect of the nonthermal desorption will be presented.