Tsunekazu Akiyoshi

Neutron Reflectivities of Ni-Mn and Ni-Ti Multilayers for Monochromators and Supermirrors

Multilayer films for neutron mirror were made by vacuum depositing thin films of Ni and Mn or Ni and Ti on a glass plate alternately. Their neutron reflectivities were measured as a function of neutron wavelength by the time-of-flight technique. For Ni-Mn multilayer monochromators, the numbers of layers necessary to give a nearly perfect reflection (≥90%) at the main Bragg peak, were found to be 7, 11 and 21 for layer thicknesses of 163, 112 and 83 A, respectively. The reflectivities obtained experimentally were compared with those calculated with the method applying the conventional optics, and their agreements were quantitatively reasonable. Moreover, for supermirrors, the numbers of layers and the distributions of layer thicknesses were examined in order to get a reflectivity of near unity down to the wavelength much shorter than the critical wavelength of a totally reflecting mirror of Ni. The reflectivity of a supermirror consisting of 160 layers of Ni and Ti was observed to behave like that of a tot...

Facility for the development of the multilayer neutron mirror at KUR

The facility for the development of the multilayer mirror as a device for handling slow neutrons is described. The facility consists of a vacuum evaporation system, a neutron reflectometer and a reflectivity calculation program. The properties of the evaporation are discussed. The neutron reflectometer makes use of the time-of-flight method and can measure the reflectivity down to 10−4. In the reflectivity calculation program, we adopt a neutron optical method with a modified optical potential, in which the contrast between layers is reduced, and the potential around the layer boundary is smoothed. It is shown that with a suitable choice of calculation parameters, experimental reflectivity of a supermirror is well reproduced by the calculation.

Multilayer mirror interferometer for very cold neutrons

Abstract The feasibility of a very cold neutron interferometer using multilayer mirrors is discussed. This device is a kind of Mach-Zehnder interferometer known in classical optics, using multilayer neutron monochromator mirror as optical elements. These mirrors consist of thin layers deposited on a very flat silicon multilayer substrate. Spacings of the multilayer are available in the range from 80 to 500 A. We discuss the characteristics of the mirror, the accuracy with which the mirror positions must be adjusted to their position and the perfection of the mirror including the present status of our development. Applications to physics are listed.

Protons from 40Ca bombarded with 14.1 MeV neutrons

Abstract Energy spectra and angular distributions were measured for protons emitted from 40 Ca bombarded with 14.1 MeV neutrons. The constant-nuclear-temperature formula for level density fits the energy distribution for backward angles and yields a nuclear temperature of 1.34 ± 0.04 MeV for 40 K. The angular distributions of the protons emitted through compound process are nearly symmetric around 90°. The spin cut-off parameter is estimated to be about 2.0 from the angular distribution of protons emitted by the (n, p) reaction. The cross sections for the (n, p) and (n, np) reactions through compound process are 471 ± 21 mb and 180 ± 32 mb, respectively. The direct (n, p) reactions has a cross section of about 11 mb.

Self-regulating characteristics of a cold neutron source with a closed-thermosiphon

Abstract This report describes self-regulating properties of the Kyoto University Reactor (KUR) Cold Neutron Source (CNS), which is cooled by a closed-thermosiphon loop of hydrogen, as are most of the CNS constructed recently. The circular moderator transfer tube is in a plane inclined about 14° to the horizontal plane. The hydrogen-helium cryogenic system of the CNS shows a self-regulating characteristic under thermal disturbances, if they are smaller than about 30% of the practical allowable heat load, 300 W at 25 K in our case. This self-regulating characteristic has been confirmed from Bodes diagram of the hydrogen pressure response in the reservoir tank to the heat load modulation. Due to this property, the liquid level in the moderator cell is kept almost constant during long term operation of the reactor. Measurements of the vertical distribution of the cold neutron flux from the moderator cell showed that a sufficient amount of liquid was stored in the cell and the ratio of the fraction of cold neutrons in the cold moderator to that in the ambient moderator was measured to be about 20 where the wavelengths are longer than 6 A using liquid hydrogen as a moderator.

Neutron optics and neutron forward-scattering using a transverse neutron-spin-echo instrument

Abstract A new principle of neutron-spin-echo (NSE) method is proposed for neutron optics and neutron forward-scattering experiments. The essential of this method is to set a sample in one of the Larmor precession fields. This sample geometry gives new physical information, in particular the refractive index of neutrons for a Si single crystal which was determined to be 1 − (1.85 ± 1.16) × 10 −5 at 5.7 A.

Magnetic field of alternately charged symmetric multipole magnet

Abstract The magnetic field of an alternately charged symmetric 2 N -pole magnet is calculated, using the conformal transformations. The formulae are given for the equipotential line, the line of force, the field strength, the magnetomotive force and the total magnetic flux passing through the surface of a pole piece.

Very cold neutron facility in horizontal arrangement with deuterium cold source

Abstract A very cold neutron guide tube with the characteristic wavelength of 23.5 A was horizontally arranged in combination with the deuterium cold source. The in-pile portion of the guide tube consists of nickel evaporated aluminum mirrors, and the external portion is made of ordinary nickel coated glass mirrors as a curved guide. The VCN output intensity and the energy spectrum are reported. The output is used for ultracold neutron production with a supermirror turbine and VCN interferometer study.

Experiments on the Existence of Di-neutrons

Dineutrons supposedly emitted in the D + T reaction were searched for at the deuteron energy of about 200 kev by detecting (1) the 2.16 min alpha activity of Bi²¹¹ from Bi²⁰⁹(n¹, gamma )Bi/sup 211/ and (2) the 1.28 Mev gamma from 6.56 min Al²⁹ nuclei produced in the reaction Al (n, gamma )Al²⁹. From the experiment no positive evidence of the cxistence of dineutrons was obtained. (W.D.M.)

Quantum beat experiments and their applications using cold neutron spin interferometer

Abstract We have carried out quantum beat experiments using cold neutron spin interferometers installed at KURRI and JAERI. Quantum beat profiles (time-dependent interference fringe) with frequencies from 20 μHz to 34 kHz were observed, which correspond to energy difference 8.271 × 10−20and 1.406 × 10−10eV. Delayed choice experiment using quantum beat are proposed as an application.