Density limitation on focusing of ground state cold H0 beams

Based on recent experimental data regarding H0 - H0 scattering at low temperatures, limits on achievable H vector0 density are shown to be substantially lower than what was previously thought. Upper density limit due to the requirement that the mean free path in the spin selection magnet must exceed the magnet size is an order of magnitude lower as a consequence of much larger collisional cross sections than those previously assumed. Additionally, transit time effects set even lower limits on densities that can be practically reached with slow beams. (author)