ULTRA-COLD NEUTRONS

Ultra-cold neutrons (UCN), i.e., neutrons with energy low enough that they undergo total reflection from a given surface at any angle of incidence, can be stored in magnetic and material bottles for periods ranging up to the neutron beta -decay lifetime ( approximately 103 s). Starting with a discussion of the theoretical and historical background the development of the field is reviewed from the first experimental observations to the present time with emphasis on the most recent developments and the remaining unsolved problems. The production and transport of UCN is discussed as well as their applications, and the direction that future developments are likely to take.