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Ultracold Neutrons—Physics and Production

Free neutrons are the most fundamental ones of the easily accessible, electrically neutral spin-1/2 systems. They take part in all the four known interactions: they strongly interact with nucleons and nuclear matter, they undergo weak β-decay, they have magnetic moments and gravitational mass. Although the neutron itself is a composite system, and thus, strictly speaking, not a fundamental particle, it is one of the finest probes for fundamental physics. Neutrons can be and are used to study all interactions, to search for new interactions, to test fundamental quantum mechanics and symmetries of nature. Over the past five decades the field of slow neutron precision physics developed and could usually make major advancements when new and more powerful neutron sources became available.