Experiment on direct nn scattering — The radiation-induced outgassing complication

The first direct neutron–neutron scattering experiment using the YAGUAR pulsed reactor has yielded initial results. They show a unforeseen significant thermal neutron background as a result of radiation-induced desorption within the scattering chamber. Thermal neutrons are mostly scattering not from other neutrons but instead from the desorbed gas molecules. Analysis of the obtained neutron time-of-flight spectra suggests neutron scattering from H2 molecules. The presented desorption model agrees with our experimental value of the desorption yield ηγ=0.02 molecules/gamma. Possible techniques to reduce the effect of the desorption background are presented.