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Neutron imaging is one of the key technologies for non-destructive transmission testing. Recent progress in the development of intensive neutron sources allows us to perform energy-resolved neutron imaging with high spatial resolution. Substantial efforts have been devoted to developing a high spatial and temporal resolution neutron imager. We have been developing a neutron imager aiming at conducting high spatial and temporal resolution imaging based on a delay-line neutron detector, called the current-biased kinetic-inductance detector, with a conversion layer 10B. The detector allowed us to obtain a neutron transmission image with four signal readout lines. Herein, we expanded the sensor active area, and improved the spatial resolution of the detector. We examined the capability of high spatial resolution neutron imaging over the sensor active area of 15 × 15 mm2 for various samples, including biological and metal ones. We also demonstrated an energy-resolved neutron image in which stainless-steel specimens were discriminating of other specimens with the aid of the Bragg edge transmission. [ABSTRACT FROM AUTHOR]

We mounted a vector-scanning superconducting quantum interference device (SQUID) sensor on a commercial SQUID microscope and successfully improved the sensitivity and spatial resolution of the sensor. Our proposed vector 3D SQUID sensor used multilayered niobium (Nb)-based technology; we realized three SQUID sensors in the structure of a vector pickup coil system on a single chip. The vector pickup coil system was built with three pickup coils that were orthogonal to one another to obtain the X, Y, and Z components of a magnetic field vector. To improve both sensitivity and spatial resolution, we attempted to reduce the inner diameter by increasing the number of windings of the pickup coils using the multilayered Nb process. The design value for the dc SQUID sensors was either the critical current density Jc = 320A cm−2 for two Josephson junctions (JJs) or the critical current Ic = 12.8 μA for the 2 μm × 2 μm JJs. To measure the current–voltage (I–V) and voltage–flux (V–Φ) characteristics of a sensor, we constructed a homemade measurement system. The fundamental characteristics of our SQUID sensors were in good agreement with the design parameters. We mounted our vector SQUID sensor on a commercial scanning SQUID microscope (SQM2000, Seiko Instrument Inc.) with a single flux-locked loop channel to test one of the three channels. We repeated the measurements three times to obtain the X, Y, and Z componential images of the magnetic field from a single vortex, and we synthesized the 3D mapping of the magnetic field vectors from a single vortex. We proved that our sensor mounted on a SQUID microscope was suitable for measuring the X, Y, and Z components of a vector magnetic field. [ABSTRACT FROM AUTHOR]

We introduce a sectoral defect into a disk (creating a Pac-Man™-shaped plate) to investigate effect of the symmetry breaking of a perfect disk on vortex dynamics. The sectoral defect acts as a preferential gateway for vortices to enter the disk. Vortices tend to form a symmetric configuration with respect to the mirror-symmetry line under various different applied magnetic fields. We found that the vortex configuration of the Pac-Man™-shaped disk exhibits an exotic arc structure, in contrast to the well-known shell structure of a disk. A characteristic of the vortex configuration is the critical number of vortices (or ‘magic number’) at which the single-arc structure becomes a multiple-arc structure, which can be tuned by changing the opening angle of the sectoral defect. We also noticed by comparing the free energies of the vortex distributions, that there are several competing metastable states with the same number of vortices when the ratio of the number of vortices in the outer arc to the number in the inner arc approaches two, for which stable triangular clusters might form part of the configurations. We conclude that there are reasonable agreements between the Ginzburg–Landau calculations and experimental scanning SQUID microscope images of vortices in de facto mesoscopic Pac-Man™-shaped Mo80Ge20 thin disks. [ABSTRACT FROM AUTHOR]

We demonstrate neutron detection using a solid-state 3He-free superconducting current-biased kinetic inductance detector (CB-KID), which consists of a superconducting Nb meander line and 10B neutron absorption layer. The CB-KID is based on the transient process of kinetic inductance of Cooper pairs induced by the nuclear reaction between 10B and neutrons. Therefore, the CB-KID can be operated in a wide superconducting region in the bias current–temperature diagram, as demonstrated in this paper. The transient change of the kinetic inductance induces the electromagnetic wave pulse under a DC bias current. The signal propagates along the meander line toward both sides with opposite polarity, where the signal polarity is dominated by the bias current direction. The full width at half maximum of the signals remains on the order of a few tens of ns, which confirms the high-speed operation of our detectors. We determine the neutron incident position within 1.3 mm accuracy in one dimension using the multichannel CB-KIDs. [ABSTRACT FROM AUTHOR]