Masahiro Hino

Measurements of ultracold-neutron lifetimes in solid deuterium.

We present the first measurements of the survival time of ultracold neutrons (UCNs) in solid deuterium (SD2). This critical parameter provides a fundamental limitation to the effectiveness of superthermal UCN sources that utilize solid ortho-deuterium as the source material. These measurements are performed utilizing a SD2 source coupled to a spallation source of neutrons, providing a demonstration of UCN production in this geometry and permitting systematic studies of the influence of thermal up-scatter and contamination with para-deuterium on the UCN survival time.

Cold Neutron Interferometry Using Multilayer Mirrors

Abstract Cold neutron interferometry using multilayer mirrors is discussed. The interferometry includes two kinds of multilayer interferometers, which are analogous optically to the Mach-Zehnder and the Jamin interferometer in classical optics. The Mach-Zehnder multilayer interferometer has been installed at JRR-3M reactor of JAERI. We describe the conditions required for the Mach-Zehnder multilayer interferometer and the characteristics of the interferometer. The Jamin multilayer interferometer, called a phase echo interferometer, shows a phase echo effect analogous functionally to the spin echo principle. We describe briefly the first successful performance tests. We propose a phase echo spin interferometer using multilayer spin splitters, based on the phase echo principle and the coherent superposition of the spin eigenstates.

Observation of the Spatial Distribution of Gravitationally Bound Quantum States of Ultracold Neutrons and its Derivation Using the Wigner Function

Ultracold neutrons (UCNs) can be bound by the potential of terrestrial gravity and a reflecting mirror. The wave function of the bound state has characteristic modulations. We carried out an experiment to observe the vertical distribution of the UCNs above such a mirror at the Institut Laue-Langevin in 2011. The observed modulation is in good agreement with that prediction by quantum mechanics using the Wigner function. The spatial resolution of the detector system is estimated to be 0.7  μm. This is the first observation of gravitationally bound states of UCNs with submicron spatial resolution.

Glassy Dynamics and Heterogeneity of Polymer Thin Films

We review our recent studies on glassy dynamics and glass transition of polymer thin films using neutron and X-ray reflectivity and inelastic neutron techniques. In the last decade extensive studies have been performed on polymer thin films to reveal very interesting but unusual properties such as reduction in the glass transition temperature T g with film thickness and negative thermal expansivity for thin films below about 25 nm, and often some contradictory experimental results have been reported. It is believed that a key to solve the controversial situation is to disclose heterogeneous structure or multi-layer structure in polymer thin films. In the review, therefore, we summarize our recent experimental results by neutron and X-ray reflectivity and inelastic neutron scattering, focusing on the dynamic heterogeneity in polymer thin films.

A resonance neutron-spin flipper for neutron spin echo at pulsed sources

Abstract We have developed a resonance neutron-spin flipper (RSF) with high frequency applicable to pulsed sources. This flipper is necessary for new neutron resonance spin echo spectrometers installed at pulsed neutron sources. The RSF works only for monochromatic neutron beams because of the dependence of its spin–flip probability on neutron velocity. The RSF can, however, be applied to pulsed neutron beam with wide band wavelength by varying the amplitude of the applied oscillating magnetic field since the pulsed neutrons are resolved into monochromatic components according to their velocity. In this paper, we describe the RSF system applicable to pulsed neutron sources, measure the flipping efficiency and discuss the experimental results.

Interfacial Width in Polymer Bilayer Films Prepared by Double-Spin-Coating and Flotation Methods

A spin-coating method with the aid of selective solvents has been used to construct multilayer structures for organic devices under the assumption that the solvents do not invade a preformed structure. To confirm the assumption, we examined the interfacial width (lambda(i)) of model polymer bilayers, composed of polystyrene and perdeuterated poly(methyl methacrylate), prepared by spin-coating and flotation methods. Neutron reflectivity measurements revealed that the lambda(i) value was larger for the spin-coating method than for the flotation method. These results cast doubt on the validity of the assumption. This knowledge should be kept in mind when this method is applied to construct multilayer structures.

Development of a Pixel Detector for Ultra-Cold Neutrons

Abstract A pixel detector with high spatial resolution and temporal information for ultra-cold neutrons is developed based on a commercial CCD on which a neutron converter is attached. 10 B and 6 Li are tested for the neutron converter and 10 B is found to be more suitable based on efficiency and spatial resolution. The pixel detector has an efficiency of 44.1 ± 1.1 % and a spatial resolution of 2.9 ± 0.1 μ m (1 sigma).

Self-regulating characteristics of a cold neutron source with a cylindrical-annulus moderator cell

The conditions, under which a cold neutron source of the ORPHEE type with a cylindrical-annulus moderator cell could have a self-regulating characteristics, were obtained through thermodynamic considerations. From an engineering viewpoint, it is not easy to establish these conditions because three parameters are involved even in an idealized system, without the effect of the mass transfer through the moderator transfer tube between the condenser and the moderator cell. The inner shell of the ORPHEE moderator cell is open at the bottom, but it is expected that only hydrogen vapor is contained in the inner shell and liquid hydrogen in the outer shell. Thermodynamic considerations show that such a state is maintained only when the liquefaction capacity of the condenser is large compared to the heat load and three parameters should be adjusted with well balance. We have proposed another type of a moderator cell which has an inner cylindrical cavity with no hole at the bottom but a vapor inlet opening at its uppermost part. In this structure, a self-regulating characteristic is easily established and the liquid level in the outer shell is maintained almost constant against thermal disturbances.

Characterization of Swollen Structure of High-density Polyelectrolyte Brushes in Salt Solution by Neutron Reflectivity

Zwitterionic and cationic polyelectrolyte brushes on quartz substrate were prepared by surface-initiated atom transfer radical polymerization of 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) and 2-(methacryloyloxy)ethyltrimethylammonium chloride (METAC), respectively. The effects of ionic strength on brush structure and surface properties of densely grafted polyelectrolyte brushes were analysed by neutron reflectivity (NR) measurements. NR at poly(METAC)/D2O and poly(MPC)/D2O interface revealed that the grafted polymer chains were fairly extended from the substrate surface, while the thickness reduction of poly(METAC) brush was observed in 5.6 M NaCl/D2O solution due to the screening of the repulsive interaction between polycations by hydrated salt ions. Interestingly, no structural change was observed in poly(MPC) brush even in a salt solution probably due to the unique interaction properties of phosphorylcholine units.

Distribution of glass transition temperature Tg in a polymer thin film by neutron reflectivity

We report neutron reflectivity results on a three-layer polystyrene thin film on Si wafer, consisting of alternative stacking of deuterated layer ~20 nm thick and hydrogenated layer ~30 nm thick. In the experiments we have evaluated the film thickness of each layer and the surface roughness and interfacial widths as a function of temperature below and above the glass transition temperature Tg. It was found that the top layer has Tg lower than the bulk Tg by ~18 K, and the middle layer has almost the same Tg as the bulk. On the other hand, the bottom layer did show very high Tg above 130 °C. The results show the distribution of Tg in the thin film. It was also found that the interfacial width between the top and middle layers increased more rapidly than that between the middle and bottom layers above ~110 °C, showing higher mobility of polystyrene in the top layer because of the lower Tg.