Filling characteristics of a neutron bottle

Because stored ultracold neutrons can now be used for precision measurements (e.g. of the neutron β-decay period) it is necessary to have a detailed knowledge of the characteristics of neutron bottles. The interest in filling arises from a requirement that for some measurements the velocity spectrum of the bottled neutrons at the end of the filling time should, ideally, be independent of bottle size. A simple model of the filling process is used to identify and find the magnitude of some relevant effects in a material walled bottle. Also, a computer simulation of the filling process is described. This is used to estimate effects that the simple model cannot deal with.