[en] Two proposals are described concerning the ultra cold neutron (UCN) experiments. The first is a magnetic neutron decelerator working with the principle of successive adiabatic spin flips of neutrons in strong magnetic fields which will produce high density polarized UCN through the multiple decelerations of cold or very cold neutrons. Another one is a fall focusing gravity spectrometer with a capability of scattering angle analysis as well as the very high energy resolution of UCN

[en] The possibility of a high resolution (δE < or approx. 10^-₇ eV) gravity spectrometer working on the principle of fall-focussing of very slow neutrons scattered in 4 π-directions is shown. The simultaneous use of time-of-flight analysis should give a higher energy resolution and also information on the scattering angle. (orig.)

[en] The rotational broadened quasi-elastic scattering spectrum of neutrons in a molecular liquid which is studied in the framework of the step formalism and the rotational diffusion approximation can be decomposed into simple Lorentzian distributions. The possibility of separately observing these terms in the experiment is discussed with respect to the numerical results of their energy broadening and amplitude for the case of liquid benzene

[en] A simple analytical model for inelastic neutron scattering in liquid hydrogen with the effects of delayed diffusion and intermolecular vibrations with a single frequency parameter is proposed. Calculated results show good agreements with experimental results of total and differential scattering cross sections as well as the energy spectra of neutrons in liquid hydrogen moderators, and thus indicate the importance of the consideration of intermolecular excitations in the dynamics of liquid hydrogen. (orig.)

[en] A system consisting of a very cold moderator and a neutron-accelerating high speed turbine is proposed for the intensification of a cold neutron beam in a medium power research reactor up to the level applicable to inelastic neutron scattering spectrometers. A numerical result for 5 cm thick solid ortho-deuterium at a temperature of about 4 K and a turbine with a blade velocity of about 350 m/s gives an output intensity of monochromatic neutrons of about 10⁷ n/cm² at an energy of about 3.5 meV with an energy width of about 0.2 meV for a typical case of a 5 MW reactor. (orig.)

[en] Results of pulsed UCN experiments with a supermirror turbine in KUR and some Monte Carlo calculations are reported. A turbine efficiency and the UCN output intensity satisfying designed values are obtained. Similar UCN experiments with a cold source at an electron linac are also carried out and compared. UCN gains by a cooled polyethylene converter are derived from the experiments. From these studies, a concept of a synchronized supermirror turbine is proposed for a spallation UCN source which can serve multi-loads uses of UCN experiments. (orig.)

[en] Recent important experience in improving the operational safety and life of a reactor are described. The Kyoto University Reactor (KUR) is a 25-year-old 5 MW light water reactor provided with two thermal columns of graphite and heavy water as well as other kinds of experimental facilities. In the graphite thermal column, noticeable amounts of neutron irradiation effects had accumulated in the graphite blocks near the core. Before the possible release of the stored energy, all the graphite blocks in the column were successfully replaced with new blocks using the opportunity provided by the installation of a liquid deuterium cold neutron source in the column. At the same time, special seal mechanisms were provided for essential improvements to the problem of radioactive argon production in the column. In the heavy-water thermal column we have accomplished the successful repair of a slow leak of heavy water through a thin instrumentation tube failure. The repair work included the removal and reconstructions of the lead and graphite shielding layers and welding of the instrumentation tube under radiation fields. Several mechanical components in the reactor cooling system were also exchanged for new components with improved designs and materials. On-line data logging of almost all instrumentation signals is continuously performed with a high speed data analysis system to diagnose operational conditions of the reactor. Furthermore, through detailed investigations on critical components, operational safety during further extended reactor life will be supported by well scheduled maintenance programs

[en] The developmental history and the present status of reactor cold sources in Japan are reviewed as well as the descriptions of the existing two reactor cold sources. One is the first cold source in Japan inserted and operated since 1987 at Kyoto University Reactor (KUR), and the other, JRR-3 cold source, is expected to start operation before this summer. A brief discussion on the future developments for cold sources is given

[en] It is shown that reflexes with form factor equal to zero are not absent, but have very small Darwin table width, which is determined by shift of the Bragg point and by form factors of another type. It is pointed out that this effect cannot be obtained within Ewald theory of dynamical diffraction on single crystals. 9 refs

[en] A new parameter α is proposed as a statistical variable of multi-dimensional reactor noise analysis. It indicates circulation in a space of state variables, while the well-known variance sigma represents the spread of distribution of fluctuations. The pair of quantities sigma and α are minimum necessary integral indices to characterize any power spectral density and are convenient for data retrieval. The α is less sensitive to the effect of low-cut filter than sigma. The analysis of experimental data by using α is demonstrated and compared with the results of theoretical treatment. (author)