Test and Development of New Production Method for Ultracold Neutrons

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Neutrons provide an important experimental opportunities in fundamental physics researches through, e.g., searches for an electric dipole moment, studies of beta decays, and observations of quantum interference phenomena. In such studies, the availability of neutrons at energies below EィイD2crィエD2 0.25 【similar or equal】μeV (ultracold neutrons, or UCN) is essential, because the spatial confinement of neutrons in a bottle for experiment is only possible for such low energies. In the present work we proposed a new method for the production of UCN, investigated its performances through computer simulations, and developed techniques for the testing and realization of its concepts.The method comprises the deceleration of neutrons through the interaction of a neutron magnetic moment and an external magnetic field. The deceleration effect is accumulated by repeating the spin flip at high- and low-field positions during the flight by means of the adiabatic passage nuclear magnetic resonance tec … More hnique. The deceleration effect is varied according to the time of flight of neutrons from a pulsed neutron source, so that the final kinetic energies converge into narrow region below EィイD2crィエD2.Computer simulations were performed for a designed setup consisting of 160 sections of superconducting magnets which implement a field alternating from 0.59 T to 4.95 T along the neutron flight path. The result shows that an about 70 times higher UCN density compared to the best density presently available in the world will be realized.Then a prototype section with a normal-conducting magnet and an rf coil for the spin flip was constructed. Solid state neutron detectors with a ィイD17ィエD1Li converter foil in front were developed for the UCN detection. Using low-energy neutron beams from the super-mirror turbine facility at Kyoto University Research Reactor Institute, an experimental study is in progress to test validity of the proposed deceleration method and to develop techniques required for it. In the runs performed up to now we have suceeded in obtaining neutrons monochromafized in a velocity range v = 4.27-5.48 m/s with a counting rate of 0.52 mcps. This result suggests that the detection of the deceleration effect will be realized with a planned setup change in the upstream neutron duct. Less