Current-biased Kinetic Inductance Detector Research Articles

Orientation mapping of YbSn3 single crystals based on Bragg-dip analysis using a delay-line superconducting sensor

Recent progress in high-power pulsed neutron sources has stimulated the development of the Bragg-dip and Bragg-edge analysis methods using a two-dimensional neutron detector with high temporal resolution to resolve the neutron energy by the time-of-flight method. A delay-line current-biased kinetic inductance detector (CB-KID) is a two-dimensional superconducting sensor with a high temporal resolution and multi-hit capability. Here, it is demonstrated that a delay-line CB-KID with a 10B neutron conversion layer can be applied to high-spatial-resolution neutron transmission imaging and spectroscopy up to 100 eV. Dip structures are observed in the transmission spectra of YbSn3 single crystals, induced by Bragg diffraction and nuclear resonance absorption. The orientation mapping of YbSn3 crystals is successfully performed via the analysis of observed Bragg-dip positions in the transmission spectra.

Superconducting neutron transmission imaging for investigating a sequential change in phase separations of low-melting Wood’s metal

We built a new cryostat system for a current-biased kinetic inductance detector (CB-KID) to be able to place a sample at room temperature for conducting the neutron transmission imaging experiments with pulsed neutrons. A Wood’s metal alloy sample (Bi 50wt.%, Pb 25wt.%, Sn 12.5wt.%, Cd 12.5wt.%) of melting temperature 75.2°C was used to check a practical test by observing fine microstructures under beam power of 812 kW at beamline BL10 of J-PARC (MLF). The Wood’s metal is composed of four phases, of which one is a Cd-rich needle-like phase of an average width of 25 µm and length of 5 mm. Since Cd is a strong neutron absorber, it is suitable for observing the fine mosaic structure contrastingly in neutron transmission imaging. After neutron-transmission imaging with the Wood’s metal in the initial state, we subsequently melted the Wood’s metal sample and solidified it again by slow cooling during the same beam time. We were successful in observing an impressive change in morphology of the phases by neutron-transmission imaging. Room-temperature sample imaging is very convenient for possible users, and is expected to be very useful for applying our CB-KID system to versatile different materials of interests.

Crystalline Orientation of CaF2 window determined by Neutron Transmission Imaging using a Delay Line Current-Biased Kinetic-Inductance Detector

The combination of a high speed two-dimensional neutron detector and an intensive pulsed neutron source provides not only neutron transmission imaging but also information on crystal structures, orientations and constituent elements by analyzing neutron transmission spectra. The delay-line current-biased kinetic-inductance detector (CB-KID) is a two-dimensional superconducting neutron detector with high spatial and temporal resolutions, and multi-hit tolerance. We demonstrated that the delay-line CB-KID with a 10B neutron conversion layer can be applied for neutron transmission measurements up to 100 keV. We observed two-different dip structures in the transmission spectra in a CaF2 single crystal, i.e., one is from the Bragg diffraction and the other is from nuclear resonance absorption. We consider that some duplicated structures in resonance absorption dips are originating from a double-bunch structure of proton pulses for producing pulsed neutrons in the accelerator.

Narrow-area Bragg-edge transmission of iron samples using superconducting neutron sensor

This study investigates a current-biased kinetic inductance detector (CB-KID) performance by investigating Bragg-edge spectra from the restricted-area neuron transmission of materials. Iron samples with a size of 5 × 5 ×2 mm3 were used as typical test materials. The ergodic theorem was used to obtain a visible transmission spectrum so that a long-time averaging of a transmission spectrum can alternatively be evaluated using a space average of independently selected area spectra with the same ensemble size. The most visible edges were observed with a limited area sample of 0.43 mm2 using a minimum time bin of 25 μs in a time-of-flight (ToF) spectrum or a wavelength resolution of 0.0007 nm of each neutron pulse at beamline BL10 of the Japan Proton Accelerator Research Complex (J-PARC) center. The main Bragg edge of iron as a sum of random 100 ensembles (with an ensemble size of 3.1 × 2.3 μm2) thus obtained has a distinctive signal-to-noise ratio and can be fitted well with the Rietveld Imaging of Transmission Spectra (RITS) program with Miller indices. We consider that our CB-KID system is, in principle, able to analyze the Bragg edge of samples as small as 3.1 × 2.3 μm2.

Neutron Imaging toward Epithermal Regime using a Delay Line Current-Biased Kinetic-Inductance Detector

Wide energy range neutron imaging and spectroscopy in a single experiment without changing the setup is available by a combination of a high-power pulsed neutron source and fast operating neutron detector. The delay-line current-biased kinetic-inductance detector (CB-KID) is a two-dimensional superconducting detector with high spatial and temporal resolutions, and multi-hit tolerance. We demonstrate that the delay-line CB-KID with 10B neutron conversion layer is applicable for neutron imaging and spectroscopy up to the neutron energy of 100 eV. High spatial neutron transmission image for a Sm-Sn mixed metal is successfully constructed below 0.3 eV. Concomitantly, we examine the neutron transmission up to 100 eV and identify observed resonance dips by Sm nuclei.

High Spatial Resolution Neutron Transmission Imaging Using a Superconducting Two-Dimensional Detector

Neutron imaging is one of the most powerful tools for nondestructive inspection owing to the unique characteristics of neutron beams, such as high permeability for many heavy metals, high sensitivity for certain light elements, and isotope selectivity owing to a specific nuclear reaction between an isotope and neutrons. In this study, we employed a superconducting detector, current-biased kinetic-inductance detector (CB-KID) for neutron imaging using a pulsed neutron source. We employed the delay-line method, and high spatial resolution imaging with only four reading channels was achieved. We also performed wavelength-resolved neutron imaging by the time-of-flight method for the pulsed neutron source. We obtained the neutron transmission images of a Gd–Al alloy sample, inside which single crystals of GdAl <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_3$</tex-math></inline-formula> were grown, using the delay-line CB-KID. Single crystals were well imaged, in both shapes and distributions, throughout the Al–Gd alloy. We identified Gd nuclei via neutron transmissions that exhibited characteristic suppression above the neutron wavelength of 0.03 nm. In addition, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{155}$</tex-math></inline-formula> Gd resonance dip, a dip structure of the transmission caused by the nuclear reaction between an isotope and neutrons, was observed even when the number of events was summed over a limited area of 15 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m × 12 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m. Gd selective imaging was performed using the resonance dip of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{155}$</tex-math></inline-formula> Gd, and it showed clear Gd distribution even with a limited neutron wavelength range of 1 pm.

Neutron Imaging for Intermetallic Alloy using a Delay Line Current-Biased Kinetic-Inductance Detector

The current-biased kinetic-inductance detector (CB-KID) is a solid-state superconducting neutron detector with high spatial and temporal resolutions, and multi-hit tolerance. We demonstrate high temperature operation of CB-KID at 7.9 K with the delay-line method. High temperature operation reduces imaging pixel size by suppressing signal propagation velocity. High spatial neutron transmission image for a mixed metal alloy consisting of heavy elements Sm and Sn is successfully constructed. We also examine the capability of element discrimination imaging based on the resonance dip analysis.

Practical tests of neutron transmission imaging with a superconducting kinetic-inductance sensor

Samples were examined using a superconducting (Nb) neutron imaging system employing a delay-line technique which in previous studies was shown to have high spatial resolution. We found excellent correspondence between neutron transmission and scanning electron microscope (SEM) images of Gd islands with sizes between 15 and 130 μm which were thermally-sprayed onto a Si substrate. Neutron transmission images could be used to identify tiny voids in a thermally-sprayed continuous Gd2O3 film on a Si substrate which could not be seen in SEM images. We also found that neutron transmission images revealed pattern formations, mosaic features and co-existing dendritic phases in Wood’s metal samples with constituent elements Bi, Pb, Sn and Cd. These results demonstrate the merits of the current-biased kinetic inductance detector (CB-KID) system for practical studies in materials science. Moreover, we found that operating the detector at a more optimal temperature (7.9 K) appreciably improved the effective detection efficiency when compared to previous studies conducted at 4 K. This is because the effective size of hot-spots in the superconducting meanderline planes increases with temperature, which makes particle detections more likely.

Homogeneity of neutron transmission imaging over a large sensitive area with a four-channel superconducting detector

We previously proposed a method to detect neutrons by using a current-biased kinetic inductance detector (CB-KID), where neutrons are converted into charged particles using a 10B conversion layer. The charged particles are detected based on local changes in kinetic inductance of X and Y superconducting meanderlines under a modest DC bias current. The system uses a delay-line method to locate the positions of neutron-10B reactions by acquiring the four arrival timestamps of signals that propagate from hot spots created by a passing charged particle to the end electrodes of the meanderlines. Unlike conventional multi-pixel imaging systems, the CB-KID system performs high spatial resolution imaging over a 15 mm × 15 mm sensitive area using only four channel readouts. Given the large sensitive area, it is important to check the spatial homogeneity and linearity of detected neutron positions when imaging with CB-KID. To this end we imaged a pattern of 10B dot absorbers with a precise dot pitch to investigate the spatial homogeneity of the detector. We confirmed the spatial homogeneity of detected dot positions based on the distribution of measured dot pitches across the sensitive area of the detector. We demonstrate potential applications of the system by taking a clear transmission image of tiny metallic screws and nuts and a ladybug. The image was useful for characterizing the ladybug noninvasively. Detection efficiencies were low when the detector was operated at 4 K, so we plan to explore raising the operating temperature towards the critical temperature of the detector as a means to improve counting rates.

Kinetic inductance neutron detector operated at near critical temperature

We previously succeeded in constructing and demonstrating the capability of a neutron imaging system based on a superconducting current-biased kinetic inductance detector (CB-KID). In the present work, we systematically studied the characteristics of the superconducting neutron detector to improve the spatial resolution and detection efficiency. We found that the number of neutron detection events with CB-KID remarkably increased when the detector temperature increased from 4 K to the critical temperature T c. We observed systematic changes of neutron signals as a function of the detector temperature from 4 K to T c. We evaluated the detection efficiency of the CB-KID detector, and compared with PHITS Monte Carlo simulations, which modeled the sequential physical processes for the 10B(n,α)7Li reaction, the transport dynamics, and the energy deposition by particles including neutrons, 4He particles, 7Li particles, photons, and electrons.

Theory for the response of a superconducting kinetic inductance detector to an electromagnetic wave packet

Voltage pulses generated by local heating due to the irradiation of an electromagnetic (EM) wave packet in a superconducting current-biased kinetic inductance detector are theoretically investigated on the basis of our previous theory [J. Phys. Conf. Ser. 1293, 012050]. The growth and decay of a hot spot created by an EM wave packet is described with the heat diffusion equation coupled with the time-dependent Ginzburg-Landau (TDGL) equation. Variation in the kinetic inductance of the current-biased stripline in the detector induced by a hot spot is explicitly derived. We clarify the characteristic feature in the shape of the voltage pulses.

Monte Carlo radiation transport modelling of the current-biased kinetic inductance detector

Radiation transport simulations were used to analyse neutron imaging with the current-biased kinetic inductance detector (CB-KID). The PHITS Monte Carlo code was applied for simulating neutron, 4He, 7Li, photon and electron transport, 10B(n, α)7Li reactions, and energy deposition by particles within CB-KID. Slight blurring in simulated CB-KID images originated from 4He and 7Li ions spreading out in random directions from the 10B conversion layer in the detector prior to causing signals in the X and Y superconducting Nb nanowire meander lines. 478 keV prompt gamma rays emitted by 7Li nuclei from neutron-10B reactions had negligible contribution to the simulated CB-KID images. Simulated neutron images of 10B dot arrays indicate that sub 10μm resolution imaging should be feasible with the current CB-KID design. The effect of the geometrical structure of CB-KID on the intrinsic detection efficiency was calculated from the simulations. An analytical equation was then developed to approximate this contribution to the detection efficiency. Detection efficiencies calculated in this study are upper bounds for the reality as the effects of detector temperature, the bias current, signal processing and dead-time losses were not taken into account. The modelling strategies employed in this study could be used to evaluate modifications to the CB-KID design prior to actual fabrication and testing, conveying a time and cost saving.

Temperature dependent characteristics of neutron signals from a current-biased Nb nanowire detector with 10B converter

We are developing a new type of the neutron imager based on a superconducting neutron detector. We previously succeeded in constructing and demonstrating neutron detection capability of a superconducting current-biased kinetic inductance detector (CB-KID). In order to improve the spatial resolution and detection efficiency, the characteristics of a superconducting neutron detector have been studied systematically in the present work. As an extension of studying the characteristics of neutron detector, we investigated temperature dependence of neutron signal such as propagation velocity and the signal amplitude as a function of time of flight (ToF) with temperature. We consider that it is important to understand the temperature dependence of the signal to improve the spatial resolution and detection efficiency of a superconducting neutron detector.

Neutron signal features of Nb-based kinetic inductance detector with 10B convertor

In our preceding works, we demonstrated successful neutron detection using a superconducting current-biased kinetic inductance detector (CB-KID), which is composed of two Nb-based superconducting meanderlines and the 10B neutron absorption layer. The CB-KID with a 10B absorption layer outputs the voltage pulses when it is irradiated by pulsed neutrons. We expected that the voltage V is proportional to a product of the bias current Ib and a time derivative of the local kinetic inductance dΔLk/dt, and a pair of signals propagate along the Nb stripline as an electromagnetic wave at a certain fraction of the light velocity c toward end electrodes. It still remains to be revealed why the signal voltage shows such a continuum in the histogram of the signal height even if the incident energy of the light ion is apparently monochromatic. In the present work, we investigated the distribution of the height and width of the signal. We found a clear correlation between height and width, which might be a key of understanding the operating principle of our detector. We consider that the origin of the signal distribution is due to the positional dependence of the light ion bombardment with respect to the meandering Nb nanowire.

Physical characteristics of delay-line current-biased kinetic inductance detector

Our preceding works reported the development of a high spatial and temporal resolution imaging system by using a current biased kinetic inductance detector (CB-KID) with the use of a delay-line technique. We called this system as a delay-line CB-KID, and succeeded in imaging of neutron events caused by the nuclear reaction and hot spots produced by using the delay-line CB-KID system. It was essentially important for our proposal to use a superconducting stripline to guide the pulsed signal where the signal propagates at a constant fast velocity along the stripline. In the present study, we intend to measure a propagation velocity of the signal along the stripline precisely to compare with the theoretical prediction of the signal propagation, which was recently developed with a superconducting waveguide S-I-S model by Koyama and Ishida [11]. Our present measurements showed a good agreement between the theoretical predictions and the experimental results on the propagation velocity as a function of temperature.

Electrodynamic theory for the operation principle of a superconducting kinetic inductance stripline detector

Generation and transmission of voltage signals in a kinetic inductance detector made of a superconducting nanowire stripline is investigated on the basis of superconducting electromagnetism. We show that electric signals traveling along the stripline in this detector can be regarded as a Swihart mode. An equation which can describe the generation and transmission of voltage pulses in this detector is derived. A pair of voltage pulses with opposite polarities are created when a spatiotemporal variation in the density of the superconducting condensate occurs in a small region of this superconducting nanowire. The voltage pulses propagate along the stripline in the directions opposite to each other with the Swihart velocity. The characteristic of the radiation detector named current-biased kinetic inductance detector (CB-KID) is well described by our model.

Neutron detection using the superconducting Nb-based current-biased kinetic inductance detector

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.

Neutron flux spectrum revealed by Nb-based current-biased kinetic inductance detector with a 10B conversion layer

We successfully derived the time-dependent flux of pulsed neutrons using a superconducting Nb-based current-biased kinetic inductance detector (CB-KID) with a 10B conversion layer at Japan Proton Accelerator Research Complex. Our CB-KID is a meander line made of a 40-nm-thick Nb thin film with 1−μm line width, which is covered with a 150-nm-thick 10B conversion layer. The detector works at a temperature below 4K. The evaluated detection efficiency of the CB-KID in this experiment is 0.23% at the neutron energy of 25.4meV. The time-dependent flux spectra of pulsed neutrons thus obtained are in good agreement with the results obtained by the Monte Carlo simulations.

Development of a neutron imager based on superconducting detectors

We succeeded in demonstrating a neutron detector based on a Nb superconducting meander line with a 10B conversion layer for a neutron imager based on superconductor devices. We use a current-biased kinetic inductance detector (CB-KID), which is composed of a meander line, for detection of a neutron with high spatial resolution and fast response time. The thickness of Nb meander lines is 40 nm and the line width is narrower than 3 mu m. The area of 8 mm × 8 mm is covered by CB-KIDs, which are assembled at the center of the Si chip of the size 22 mm × 22 mm. The Nb CB-KIDs with a 10B conversion layer output the voltage by irradiating pulsed neutrons. We have investigated γ/n discrimination of a Nb-based CB-KID with 10B conversion layer using a Cd plate, which indicates that a CB-KID can operate as a neutron detector under the strong γ-ray fields.

Neutron detection using a current biased kinetic inductance detector

We demonstrate neutron detection using a solid state superconducting current biased kinetic inductance detector (CB-KID), which consists of a superconducting Nb meander line of 1 μm width and 40 nm thickness. 10B-enriched neutron absorber layer of 150 nm thickness is placed on top of the CB-KID. Our neutron detectors are able to operate in a wide superconducting region in the bias current–temperature diagram. This is in sharp contrast with our preceding current-biased transition edge detector, which can operate only in a narrow range just below the superconducting critical temperature. The full width at half maximum of the signals remains of the order of a few tens of ns, which confirms the high speed operation of our detectors.