Jun-ichi Suzuki

Focusing and polarized neutron small-angle scattering spectrometer (SANS-J-II). The challenge of observation over length scales from an ångström to a micrometre

SANS-J (a pinhole small-angle neutron scattering spectrometer at research reactor JRR3, Tokai, Japan) was reconstructed as a focusing and polarized neutron small-angle scattering spectrometer (SANS-J-II). By employing focusing lenses of a biconcave MgF2 crystal or of a sextupole permanent magnet and a high-resolution photomultiplier, the minimum accessible magnitude of the scattering vector qmin was improved from 3 × 10−3 A−1 to an ultra-small-angle scattering (USAS) of 3 × 10−4 A−1. Compared with a Bonse–Hart double-crystal method, the advantages of focusing USAS are the efficient detection of anisotropic USAS with an area detector, an improvement in q resolution Δq/q at conventional magnitudes of the scattering vector q ~ 10−3 A−1 and a gain in neutron flux in the conventional q region of q ~ 10−3 A−1.

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 scintillation imaging device for cold neutrons

Abstract As an application of the wavelength-shifting (WLS) fiber technique recently developed in the field of high-energy physics, a novel type of imaging device for neutrons has been successfully investigated; a space resolution of 1 mm FWHM with detection efficiency of 55% for 10 A neutrons has been experimentally confirmed with a prototype made of a 0.5-mm-thick ZnS(Ag)+6LiF scintillator plate optically coupled to WLS fiber arrays. In addition to promising results obtained in this study, its simple structure and reliable operation allow us to foresee a new generation of imaging devices to meet the increasing demand for large-area and high space-resolution imaging devices for several new projects on spallation neutron sources in the world.

Atomic ordering in FeSr2LnCu2O6+δ system (Ln = Nd, Y and Er)

Abstract FeSr2YCu2O6+δ exhibits superconductivity around 50 K, when it is properly annealed in N2 atmosphere and subsequently in O2 atmosphere under ambient and high pressure. Neutron powder diffraction study shows that N2-annealing causes ordering of Cu and Fe, and that O2-annealing and oxidizing under high pressure supply the charge on the CuO2 sheets. Recently, we have found a superstructure in the sample N2-annealed within a particular temperature range. Electron diffraction study indicates that it has an orthorhombic structure with the unit cell of 2 a× 2 a×2c as compared with the tetragonal FeSr2YCu2O6+δ structure with the unit cell of a×a×c. Neutron powder diffraction study indicates that it has the CoSr2YCu2O7-type structure with the FeO4 tetrahedron, due to not only ordering of Cu and Fe but also oxygen ordering on the FeOδ sheet, which is consistent with the electron diffraction study. We have also obtained the similar superstructure in FeSr2ErCu2O6+δ, but the situation is different in FeSr2NdCu2O6+δ which does not exhibit superconductivity even after O2-annealing and oxidizing. Atomic ordering in the FeSr2YCu2O6+δ system is influenced by the size of the ionic radius in the Y site, which is effective on the occurrence of superconductivity.

A focusing-geometry small-angle neutron scattering instrument with a magnetic neutron lens

We have constructed a focusing-geometry small-angle neutron scattering (FSANS) instrument, SANS-J-II, with two kinds of neutron focusing device: a series of compound refractive lenses made of MgF2 and a magnetic neutron lens based on an extended Halbach-type sextupole magnet. In this study, we investigated the performance of the FSANS instrument with the magnetic neutron lens. The intensity distribution of a direct neutron beam focused on the detector plane by the magnetic neutron lens had a ratio of the peak height to the background level of \sim\!6\times 10^4 for a polarized neutron beam with a polarization degree of \sim \!0.99. It is found that a minimum value of the measurable q range [where q is the modulus of the scattering vector and is defined as q = (4\pi/\lambda)\sin(\theta/2), where \theta is the scattering angle and \lambda is the neutron wavelength], q_{\rm min}, of 6.5 \times 10^{-4} A−1 can be achieved by the FSANS instrument with the magnetic neutron lens using neutrons with \lambda = 6.6 A and \Delta \lambda/\lambda = 0.13 for the full width at half maximum.

Cold neutron imaging detection with a GSO scintillator

Abstract The pulse-height spectrum and two-dimensional image of a 0.5 mm thick GSO scintillator were investigated for a 6 A cold neutron beam. The 31 and 81 keV peaks resulting from neutron absorption by Gd nuclei were identified in the pulse-height spectrum by using a photomultiplier tube. Images of 1.5 and 2.1 mm (FWHM) in diameter were observed for 1 and 2 mm diameter incident beams with an image intensifier and viewed by a CCD camera, corresponding to a position resolution of 1.3 mm (FWHM). The result implies that a position resolution of better than 100 μm would be achievable by employing a GSO scintillator thinner than 20 μm .

Micromagnetic domain observations of Co-Cr films by neutron scattering

Magnetic microstructures revealed by neutron small angle scattering are correlated with the compositional separation (CS) in sputtered Co-22at%Cr thin films for high density magnetic recording. The CS is confirmed to be strongest for deposition temperatures from 150/spl deg/C to 400/spl deg/C, using nuclear magnetic resonance. The finest magnetic particles, less than 10 nm in diameter, are detected in a film deposited at 200/spl deg/C, in good agreement with the smallest features observed in the etched microstructure by transmission electron microscopy. This indicates that CS produces magnetic grains much smaller than the crystal grains which can, therefore, be applied to synthesize Co-Cr thin film media for ultra high density magnetic recording. >

Development of a Fresnel lens for cold neutrons based on neutron refractive optics

Abstract We have developed compound refractive lenses (CRLs) for cold neutrons, which are made of vitreous silica and have an effective potential of (90.1– 2.7×10 −4 i ) neV . In the case of compound refractive optics, neutron absorption by the material deteriorates lens performance. Thus, to prevent an increase in neutron absorption with increasing beam size, we have developed Fresnel lenses using the electrolytic in-process dressing grinding technique. The lens characteristics were carefully investigated with experimental and numerical simulation studies. The lenses functioned as a neutron focusing lens, and the focal length of 14 m was obtained with a 44-element series of the Fresnel lenses for 10 A neutrons. Moreover, good neutron transmission of 0.65 for 15 A neutrons was obtained due to the shape effect. According to comprehensive analysis of the obtained results, it is possible to realize a CRL for practical use by choosing a suitable lens shape and material.

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.