Tomohiro Adachi

Upgrade of the 32 m small-angle neutron scattering instrument SANS-U

The small-angle neutron scattering instrument, SANS-U, owned by the Institute for Solid State Physics, The University of Tokyo, has been upgraded. The SANS-U is a 32 m SANS instrument installed in 1991 at the guide hall of the JRR-3M research reactor of the Japan Atomic Energy Research Institute, and has been serving for inter-university cooperative research use since 1993. The major upgrades include (i) replacement of the two-dimensional area detector by a multi-wire type position-sensitive proportional counter, (ii) renewal of the operating system from a VAX and sequencers to an integrated PXI system controlled by LabVIEW-RT software, (iii) a focusing collimation system, and (iv) a variety of accessory equipment. These upgrades provide a wide dynamic range of neutron counting, user-friendly operation and real-time circular averaging of two-dimensional data.

Structure and dynamics of hexafluoroisopropanol-water mixtures by x-ray diffraction, small-angle neutron scattering, NMR spectroscopy, and mass spectrometry

The structure and dynamic properties of aqueous mixtures of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) have been investigated over the whole range of HFIP mole fraction (xHFIP) by large-angle x-ray scattering (LAXS), small-angle reutron scattering (SANS), 19F-, 13C-, and 17O-NMR chemical shifts, 17O-NMR relaxation, and mass spectrometry. The LAXS data have shown that structural transition of solvent clusters takes place at xHFIP∼0.1 from the tetrahedral-like hydrogen bonded network of water at xHFIP⩽∼0.1 to the structure of neat HFIP gradually formed with increasing HFIP concentration in the range of xHFIP⩾0.15. The Ornstein–Zernike plots of the SANS data have revealed a mesoscopic structural feature that the concentration fluctuations become largest at xHFIP∼0.06 with a correlation length of ∼9 A, i.e., maximum in clustering and microhetrogeneities. The 19F and 13C chemical shifts of both CF3 and CH groups of HFIP against xHFIP have shown an inflection point at xHFIP∼0.08, implying that the environment of ...

Development of a neutron detector based on a position-sensitive photomultiplier

A neutron scintillation detector based on a position-sensitive photomultiplier has been developed for neutron spin echo and small angle neutron scattering measurements. This photomultiplier has good spatial resolution, less than 1 mm2. The detection efficiency of gamma ray background is very low for using a thin ZnS/6LiF scintillator. The effective area of this detector is around 60 cm2.

Cold neutron beam focusing by a superconducting sextupole magnet

We have developed a superconducting sextupole magnet with about 50 mm in bore diameter to focus cold neutron beams with large cross-section and have investigated its focusing and polarizing effect. Large gain in neutron intensity and high neutron polarization have been obtained by numerical simulation for highly collimated neutron beams. We discuss applications of this magnet for small-angle neutron scattering experiments.

Development of a high-resolution scintillator-based area detector for neutrons

We applied a scintillator-based area detector to the neutron time-of-flight method by developing a new electronics system for this detector, which detector consists of a thin plate of ZnS(Ag)+6Li scintillator optically coupled to wavelength shifter. The spatial resolution was about 0.4 mm which is consistent with a fiber width of 0.4 mm. The detection efficiency for thermal neutrons was about 6%. A good-resolution radiographic-image as a function of flight time was obtained.

Development of neutron optical devices

Recent results on the development of the neutron optical devices utilizing the neutron refraction in an inhomogeneous magnetic field and in the material surface are described.

Development of a spin flipper for an application of a neutron magnetic device

We have developed a radio-frequency gradient spin flipper for the effective utilization of the focused and polarized neutron beam obtained using a superconducting sextupole magnet developed for the practical application in the neutron-scattering experiment. The flipper was designed to be effective for the neutron beam with wavelengths longer than 4 A and the cross section of 50 mm in diameter. The flipper was tested using polarized cold neutrons, and good performance was obtained.

Recent progress in the development of concave Fresnel lenses for neutrons

The performance of a Fresnel-type compound refractive lens for focusing cold neutrons was evaluated. The lens consists of 44 pieces of compound Fresnel-type refractive lenses made of MgF2 single crystals. The intensity profile of the diffracted neutrons measured over the wavelengths of 9-14 A was compared with the results of numerical simulations. Good neutron transmission of 0.85 for 9 A neutrons and a focal length of 3.4 m for 16 A neutrons were achieved.

Development of a magnetic lens and prism for cold neutrons and their application to neutron scattering experiments

We have been developing a neutron lens and prism based on neutron refractive optics. As a neutron has a magnetic dipole moment, it is accelerated in a magnetic field gradient. Thus, we can control a neutron beam free from beam attenuation using the magnetic field gradient. Moreover, its spin dependence of the acceleration is profitable in the case of using the polarized neutron beam. The sextupole magnetic field functions as a focusing or defocusing lens for neutrons depending on the neutron spin states. The focusing and defocusing effects of a prototype sextupole magnet was experimentally studied. By combining focusing and defocusing functions of the sextupole magnet, we can control the neutron beam shape and divergence more flexibly. Adiabatic and nonadiabatic field connections make it possible to realize the magnetic doublet system. A quadrupole magnetic field functions as a neutron prism, which were experimentally confirmed. The neutron spin and energy dependence of the refracting power is applicable to an analysis of the neutron spin and energy. In this paper, the details of the experimental results of the magnetic devices are described and their applications in the neutron scattering experiment are discussed.

A New Fabrication Method of Neutron Fresnel Lens

In order to improve the application of neutron scattering technique, a new neutron optical device, which optical system consists of an array of several ten neutron Fresnel lenses, is designed by the researcher engaging in the study of neutron optics. Neutron Fresnel lenses for this new device have the same symmetric concave form. Its center is a spherical surface and the other surfaces are conic section. MgF2 single crystal glass is selected as the material for making neutron Fresnel lens because of its high transparence. Considering the form complicity and the brittle properties of MgF2 material, the fabrication of neutron Fresnel lens is of very difficulty. Form ELID (electrolytic in-process dressing) grinding was used for grinding the neutron Fresnel lens in this first study. The optima of grinding conditions for #325, #1200 and #4000 cobalt bonding diamond abrasive wheels are obtained through a series of tests. The MgF2 material is removed at the ductile mode by using #4000 abrasive wheel. Thus, the neutron Fresnel lens fabricated has low roughness and high transparence. The transmission of an array of 50 pieces of neutron Fresnel lens is 92.5 percents to neutron beam with wavelength 5Å and 79.3 percents to 16Å.