Polarized Neutron Beam Research Articles

Impact of Isotopic Exchange on Hydrated Protein Dynamics Revealed by Polarized Neutron Scattering

Within the last decades, it was often assumed that in hydrogen-rich disordered samples, such as proteins in solution or hydrated powder form, incoherent neutron scattering from hydrogen nuclei dominated the scattering signal to an extent that allowed all other contributions to be neglected. As incoherent scattering arises solely from self-correlations, it further justified such a choice. Consequently, heavy water was often used as a contrast tool to highlight molecular motions in live samples. Coherent scattering, which implies the scattering from many nuclei and therefore collective processes, is another non-negligible contribution to neutron scattering where cross sections of other nuclei than hydrogen are significant. The recent advent of instrumentation based on polarization of neutron beams and the analysis of their polarization state after scattering for dynamical studies allows us to separate and shed light on the two contributions. In the present study we reveal that, unexpectedly, the isotopic exchange of water in the hydration shell of proteins arises on a much faster timescale than assumed so far. Moreover, the collective and local D-bond network relaxation of hydration water contributes to a high extent to the coherent scattering signal, at odds with usual “static” approaches used to estimate the relative impacts of dynamics in the sample. Hence, hydration water necessarily contaminates nonpolarized standard experiments. The findings are of paramount importance for all neutron scattering experiments where partial or full deuteration is used. Published by the American Physical Society 2024

(Invited) Direct Bonding and Its Interface for High-Density Integration of Superconducting Qubits

Superconducting qubits are one of the intensive approaches to fabricate quantum computing (QC). Qubits can be manufactured by the current Si-based semiconductor manufacturing processes. However, circuits should be superconducting material such as Nb (Tc=9.29 K), Al (Tc=1.18 K), Pb (Tc=7.2 K), In (Tc=3.4 K) , etc. In current technology, qubits are arranged in planar geometry in a chip, and each qubit should wire to control and read signal lines in the same plane. When a large number of qubits are integrated, these wires would be too constrained, and several problems would be actualized, such as wiring for qubits located at the chip center, crosstalk among wiring, and so on. The signal integrity for the QC devices is much better to have qubits at short distances from the control circuitry. Therefore, 3D wiring is required for a large-scale qubit integration. 3D integration of qubits with interposer chips by flip-chip bonding is the proof-of-concept of the large-scale qubit integration. The 3D integration approaches for qubit- based devices are the same as conventional electronic devices, including the through silicon via (TSV) process for interposers and micro bump flip-chip bonding. However, they use superconducting metals instead of copper and other non-superconducting materials. Most flip-chip microbump bonding processes require thermal compression at over 170 °C. Superconducting elements are easily degraded by heat. Consequently, we apply surface activated bonding (SAB) to a superconducting metal as a low-temperature bonding process for superconducting circuits.The test element group (TEG) for the current-voltage (I-V) measurement of the bonded interface was bonded by SAB method, and at the Nb SAB interface layer is a 2- to 3-nm-thick amorphous layer and the layer consist of Si-rich interfacial layer compared to the Nb bulk area. The bonding specimens were activated on jigs made of Si during the bonding process; then the Si sputtered by FAB was redeposited on the bonding surfaces. Furthermore, the bonded specimen was wired using Al wire to a chip carrier with a stage installed into a 0.3-K cryostat. As a result, the Tc of this path is 9.3 K, which is very similar to that of Nb bulk (9.2 K). However, a small step of the Tc at 9.1-9.4 K was also observed. (Fig.1) [1]In this study, we discuss the superconducting interface of direct bonded Nb-Nb by Tc, and also the interfacial structure measured by polarized neutron reflectometry (PNR). The results show clear spin asymmetry in the superconducting state, as splitting is observed in the fringes of the parallel neutron (neutron spins parallel to the external magnetic field 0.1 T) reflection R+ and the antiparallel (neutron spins antiparallel to it) reflection R−, where the latter has become larger. This well-known effect is related to the flux penetration in the superconducting state. Therefore, unique information about the superconducting state of the buried thin film can be measured by using the polarized neutron beam. For this project the major advantage of PNR will be to characterize the superconducting state at the deeply buried Nb interfaces, sandwiched between the two substrate wafers, which would be infeasible using alternate techniques.[1] M. Fujino, et. al., J. Appl. Phys., 133, 015301, 2023 Figure 1

Neutron Nanomediators for Non-Invasive Temperature Mapping of Fuel Cells

Polymer electrolyte fuel cells (PEFCs) have gained significant attention in the past century for their ability to convert hydrogen chemical energy into electrical energy. However, the technology still requires refinement due to losses in polarization, ohmic resistance, and mass transport that result in heat generation, negatively affecting the device water management and durability. To better understand these processes, researchers initiate studies to improve knowledge of the temperature at the cell structure core. However, current methods using micro-thermocouples [1] are highly invasive, impeding cell operation and limiting data accuracy.The project aims to overcome the latter problem using ferromagnetic nanoparticles for non-invasive temperature mapping on these devices. A key part of this novel method is the application of Neutron Imaging through a polarized beam [2], which allows to detection of the temperature distribution on the surrounding nanosensors. The dispersed ferromagnetic nanomediators, in these conditions, depolarize the incoming neutron beam due to the random magnetic field produced by the nanoparticles themselves. Furthermore, as the temperature rises toward the Curie temperature (Tc), the nanosensors tend to lose their magnetic preferential orientation, influencing the neutron beam polarization gradually less as the ambient temperature increases.This project includes identifying a suitable material, synthesizing nanoparticles through solution techniques [3], and performing physical and magnetic ex-situ characterizations. By dispersing them in Polytetrafluoroethylene micro-powders, nickel, iron, and Nd2Fe14B alloys were initially studied at different concentrations, grain sizes, and magnetic environments, showing promising signal detection (η) and absolute thermal variation (Δη) results.

Development and first results of a magnetic sample environment for polarized neutron imaging of thin metal sheets

Polarized neutron imaging brings the great advantage of analyzing bulk magnetic properties with good spatial resolution. The technique is based on the interaction of the neutron spin with magnetic samples or free magnetic fields and observing the changes to a spin-polarized neutron beam. The high sensitivity to even small magnetic fields is a benefit in obtaining magnetization information but simultaneously a challenge in instrumentation, since magnetic environments for the polarized neutron beam and for the sample, as well as the fringe field from the magnetic sample itself all affect the measurement and can give rise to unwanted effects. We have used finite element simulations and ray tracing simulations, to design and analyze a magnetic sample environment devised for the measurement of ferromagnetic metal sheets. Here we show an analysis of performance of the experimental setup based on the simulation results and compare them to first experimental results on a grain oriented silicon steel sample.

Insight into the negative magnetization and anomalous exchange-bias in DyFe5Al7 through neutron depolarization and neutron diffraction studies

We have provided the mesoscopic and microscopic understandings of polarity reversal of the magnetization or negative magnetization (NM) below T COMP = 93 K in an exotic magnetic material containing three magnetic sublattices, viz., DyFe5Al7 crystallizing in ThMn12 structure, using neutron depolarization and neutron diffraction techniques. A full recovery of the neutron beam polarization at the T COMP in a neutron depolarization experiment reveals a total compensation of magnetization inside the magnetic domains in the sample. The temperature-dependent neutron diffraction study under zero magnetic field has provided temperature dependencies of antiparallelly coupled Dy (M Dy(2a)) and Fe (M Fe(8f) and M Fe(8j)) sublattice magnetic moments along [100] direction. The dominance of |M Dy(2a)| over total Fe moment, , below T COMP leads to the NM in the compound. The magnetization versus magnetic field curves below the T COMP indicate the presence of field-induced spin reorientation in the compound. The magnetic field required for spin reorientation (H SR) is maximum at the lowest temperature and it decreases to zero as the temperature is increased to T COMP. Interestingly, the compound shows a finite exchange-bias (H EB) below the T COMP only, as evident from the field-cooled hysteresis loops, while at T > T COMP, H EB is almost zero. The cooling-field (H COOL) dependent study of H EB shows a slope change at H COOL ∼ H SR indicating a correlation of exchange-bias with spin-reorientation in the compound. This study, apart from revealing microscopic understanding of magnetic behavior of an exotic three magnetic sublattice system, provides a correlation among exchange-bias, magnetic compensation, and spin-reorientation phenomena.

Temperature dependent partially compensated to nearly fully compensated magnetic state in half-metallic full Heusler alloy, Mn1.2Fe1.18V0.62Al

We report experimental and theoretical studies of magnetization compensation phenomenon in quaternary Heusler alloy Mn1.2Fe1.18V0.62Al by employing dc magnetization, neutron depolarization, neutron diffraction, specific heat, electrical resistivity, and electronic structure calculation. In this ferrimagnetic alloy system with ordering temperature TC = 360 K, the asymmetric thermal variations of the site magnetic moments provide an evidence of the partially compensated magnetic state of the system down to ∼ 48 K. However, below 48 K, the system exhibits its magnetic ground state with the negligibly small ordered moment of 0.05(5) μB/f.u. at 10 K, as obtained from the neutron diffraction study. Nearly full recovery of neutron beam polarization at 4 K in the neutron depolarization study also infers a nearly fully compensated magnetization state in this Heusler alloy. Temperature dependent specific heat and resistivity measurements also corroborate with the dc magnetization study representing 48 K as a turning point at which the system reaches its ground state. The electronic structure calculations, using the SPR-KKR Green’s function approach, verify the half-metallic nature of the present system. The net magnetic moment (0.06 μB/f.u.) obtained from the theoretical calculations as well as neutron diffraction experiments (0.05 μB/f.u.) is in good agreement with the Slater-Pauling rule (0.06 μB/f.u.). This small magnetic moment of the system (Mn0.82Fe1.18)(Mn0.38V0.62)Al proclaims to be a nearly compensated ferrimagnetic system with 23.94 valence electrons. Such magnetically compensated systems with finite spin polarization could be favorable for spintronics applications.

Z+: Neutron cross section separation from wide-angle uniaxial polarization analysis.

We introduce a simple method to extract the nuclear coherent and isotope incoherent, spin incoherent, and magnetic neutron scattering cross section components from powder scattering data measured using a single neutron beam polarization direction and a position-sensitive detector with large out-of-plane coverage. The method draws inspiration from polarized small-angle neutron scattering and contrasts with conventional so-called "xyz" polarization analysis on wide-angle instruments, which requires measurements with three orthogonal polarization directions. The viability of the method is demonstrated on both simulated and experimental data for the classical "spin ice" system Ho2Ti2O7, the latter from the LET direct geometry spectrometer at the ISIS facility. The cross section components can be reproduced with good fidelity by either fitting the out-of-plane angle dependence around a Debye-Scherrer cone or grouping the data by angle and performing a matrix inversion. The limitations of the method and its practical uses are discussed.

A non-depolarizing CuTi neutron supermirror guide for PERC

Neutron guides are used to transport slow neutrons from sources to experiments. Conventional neutron supermirror guides use alternating thin layers based on nickel and titanium. Due to the magnetic properties of nickel, their neutron reflection properties are spin-dependent, in particular when exposed to high magnetic fields. Motivated by the requirements of precision experiments on neutron beta decay, we present novel supermirrors based on copper and titanium, which preserve the neutron beam polarization. These show excellent reflectivity and prove to be very stable even when exposed to high temperatures.

Additively Manufactured NdFeB Polyphenylene Sulfide Halbach Magnets to Generate Variable Magnetic Fields for Neutron Reflectometry.

Halbach arrays are the most efficient closed structures for generating directed magnetic fields and gradients, and are widely used in various electric machines. We utilized fused deposition modeling-based Big Area Additive Manufacturing technology to print customized, compensated concentric Halbach array rings, using polyphenylene sulfide-bonded NdFeB permanent magnets for polarized neutron reflectometry. The Halbach rings could generate a 0 ≤ B ≤ 0.30 T field, while preserving 90% polarization of an axial neutron beam. Polarized neutron beams are used to study a wide range of structural and magnetic phenomena spanning physics, chemistry, and biology. In this study, we demonstrate the effectiveness of additive manufacturing for producing prototype Halbach arrays, characterize their magnetic properties, and generated magnetic fields, and discuss the conservation of neutron beam polarization as a function of magnetic field.

New design of a magnetic device for wide-angle XYZ polarization analysis PASTIS-3, from the concept to first tests with thermal neutrons

We present the new concept and neutron test results of the third generation PASTIS device for XYZ wide-angle polarization analysis for thermal neutrons. PASTIS-3 uses two polarized 3He Neutron Spin filter Cells (NSF) for polarizing and analyzing neutrons spins, flipping the incident neutron beam polarization by reversing the 3He spin state of the polarizing entrance cell. We detail a new coil design for high spatial homogeneity of the magnetic field in any field direction, and the calculation method employed to optimize the geometry and to characterize the field gradients. Various components of the apparatus are described with particular attention to their performance and impact on the relaxation time of the NSF cells. Finally, we present test results of the new device tested on the thermal triple-axis spectrometer IN20 at the ILL.

Novel approach to neutron electric dipole moment search using weak measurement

We propose a novel approach in a search for the neutron electric dipole moment (EDM) by taking advantage of signal amplification in a weak measurement, known as weak value amplification. Considering an analogy to the weak measurement that can measure the spin magnetic moment interaction, we examine an experimental setup with a polarized neutron beam through an external electric field with spatial gradient, where the signal is sensitive to the EDM interaction. In particular, a dedicated analysis of effects from impurities in pre- and post-selections is performed. We show that the weak value amplification occurs where the signal is enhanced by up to two orders of magnitude, and demonstrate a potential sensitivity of the proposed setup to the neutron EDM.

Realizing a (nearly) 100% neutron beam polarization

We report a neutron beam polarization P = [99.9982 ± 0.0024]%, which means an improvement of two orders of magnitude compared to known values. Actually, one can assume this neutron beam to be 100% polarized, because due to the special beam guidance the overlap of spin-up neutrons and spin-down neutrons could be suppressed down to 1.2 × 10−12 [rel. units]. These values are about four orders of magnitude below the detection limit of a monochromatic neutron flux of 108n· cm−2s−1.

SANS and neutron diffraction study of ausformed EUROFER97/2 ferritic/martensitic steel

Abstract Small-angle neutron scattering (SANS) and neutron diffraction have been utilized for micro-structural characterization of Eurofer97/2 heats submitted to thermo-mechanical treatments, with the aim to investigate macroscopic material volumes and to complete the local information provided by scanning electron microscopy. The measurements were carried out at MLZ in Garching, utilizing for SANS also a polarized neutron beam. The investigated samples had been submitted to austenitization and tempering at different temperatures, as well as to double austenitization and to “ausforming”, that is austenitization followed by hot rolling. For most of the examined treatments, nearly identical SANS cross-sections were measured, close to the one of Eurofer97/1. In the ausformed sample the nuclear SANS cross-section is also nearly identical to the other samples but the magnetic one is one order of magnitude higher. Furthermore, over a wide experimental interval its nuclear-magnetic interference, measured by polarized SANS, is of opposite sign with respect to the non-ausformed samples. Neutron diffraction measurements provided strong evidence that the origin of such effects is due to the presence of the non-magnetic austenite phase in the ausformed sample, with an estimated volume fraction of 0.17 ± 0.02; within the experimental resolution, it disappears after subsequent tempering.

Sensitive neutron transverse polarization analysis using a 3He spin filter.

We report an experimental implementation for neutron transverse polarization analysis that is capable of detecting a small angular change (≪10-3 rad) in neutron spin orientation. This approach is demonstrated for monochromatic beams, and we show that it could be extended to polychromatic neutron beams. Our approach employs a 3He spin filter inside a solenoid with an analyzing direction perpendicular to the incident neutron polarization direction. The method was tested with polarized neutron beams and a spin rotator placed inside a μ-metal shield just upstream of the analyzer. No cryogenic superconducting shields or additional neutron spin manipulations are needed. With a counting detector, we experimentally show that the angular resolution δθ=1/(PnAN) rad is only determined by the counting statistics for the total counts N and the product of the neutron polarization Pn and the analyzing power A. With a high-flux neutron beam, 10-6 rad angular sensitivity is feasible within a day. This simple, classical-quantum-limited transverse polarization analysis scheme may reduce the overall complexity of experimental implementation for applications requiring sensitive neutron polarimetry and improve the precision in fundamental science studies and polarized neutron imaging.

Polarization preservation of polarized deuteron beams in the electron ion collider at Brookhaven National Laboratory

The physics program at the future electron ion collider (EIC) calls for polarized neutron beams at high energies. The best neutron carriers are $^{3}\mathrm{He}$ nuclei and deuterons. Both neutron carriers are expected to be utilized by the spin physics program in the EIC. Owing to the small magnetic moment anomaly of a deuteron particle, significantly higher magnetic fields are required for spin rotation, so that full Siberian snakes are not feasible. However, the resonance strengths are weak, and the number of resonances is small. It is possible to deal with individual resonances using conventional methods such as a betatron tune jump and vertical ac dipole for intrinsic depolarizing resonances, and a weak partial snake for imperfection resonances. This study employed a realistic magnet ramp rate and parameters (both transverse and longitudinal emittances, as well as realistic lattices) to show that it is possible to accelerate polarized deuterons beyond 100 GeV/n. This paper summarizes the details of the feasibility of a polarized deuteron beam for the future EIC at Brookhaven National Laboratory.

Polarized beam option for the time-of-flight spectrometer NEAT

We present the basic design of the incoming neutron beam polarizer system recently installed at the TOF spectrometer NEAT at HZB and the first experimental test results. The recent upgrade of the instrument resulted in beam flux on the sample, which is one of the highest worldwide for this class of instruments. The substantial intensity gain obtained in the upgrade provides good conditions for polarized neutron experiments, considering the inherent cuts of neutron intensity by polarizing the beam. The neutron beam polarizer is placed inside a 3.8 m long evacuated neutron “guide changer”, which allows us to move into the beam delivery guide one of 3 alternative straight neutron guide sections mounted in parallel on a linear translation stage. The new transmission polarizer takes up the inside volume of a 1.33 m long, 60 mm x 125 mm cross section straight guide portion. The focusing of the beam after the polarizer to the 30 mm x 50 mm sample area happens over a total length of 3.5 m, of which 2.92 cm is a converging guide assembly with m=4 supermirror coating and parabolic end. This guide section leaves 58 cm space between guide exit and sample axis for sample environment equipment, in particular for high field cryomagnets. The transmission polarizer contains 8 “V cavity” channels with non-polarizing supermirror coated, opaque side walls and neutron-transparent Si cavity plates, coated by m=3 polarizing supermirror on both sides. The nominal operational wavelength band width of the polarizer is 2.5 – 8 Å, with measured polarization efficiency between 92 and 96 % for well collimated beam. The beam transmission efficiency for the preferred neutron spin state is about 65 %. The first 110 cm of the neutron spin guide field after the exit of the polarizer is provided by the stray fields of the magnet around the polarizer and of a permanent guide field magnet acting in the same direction. This section contains a wavelength tunable single coil Mezei flipper with flipping efficiency > 99 %. The rest of the guide field magnets are solenoids around the glass neutron beam guide. The supermirror coating in the polarized neutron section of the beam guide has been manufactured using a non-magnetic Ni alloy, the guide exchanger housing and its mechanical parts are made of non-magnetic alloys, primarily stainless steel. The polarized beam delivery system is by now operational and it is available for polarized neutron beam experiments on samples in a magnetic field. A 14 T vertical field cryomagnet is on hand at the HZB Sample Environment Group for use on NEAT. The NEAT sample chamber has been designed and built with non-magnetic or weakly magnetic materials in order to allow both for polarized neutron beam experiments and for polarization analysis work.

A strategy for handling aberration in Spherical Neutron Polarimetry

We present a strategy for identifying and correcting for aberration effects in Spherical Neutron Polarimetry. The transformation of the neutron beam polarization vector due to scattering from a material is determined with Spherical Neutron Polarimetry. This neutron scattering technique measures the three cardinal components of the scattered polarization for any chosen cardinal direction of the incident polarization for a given Bragg reflection. As a consequence, the instrumentation required for this technique is desired to be capable of measuring the three-dimensional polarization vector over the sphere. As with all instrumentation, the field of measurement is subject to aberration which must be characterized.

Visualization and quantification of inhomogeneous and anisotropic magnetic fields by polarized neutron grating interferometry

The intrinsic magnetic moment of a neutron, combined with its charge neutrality, is a unique property which allows the investigation of magnetic phenomena in matter. Here we present how the utilization of a cold polarized neutron beam in neutron grating interferometry enables the visualization and characterization of magnetic properties on a microscopic scale in macroscopic samples. The measured signal originates from the phase shift induced by the magnetic potential. Our method enables the detection of previously inaccessible magnetic field gradients, in the order of T cm−1, extending the probed range by an order of magnitude. We visualize and quantify the phase shift induced by a well-defined square shaped uniaxial magnetic field and validate our experimental findings with theoretical calculations based on Hall probe measurements of the magnetic field distribution. This allows us to further extend our studies to investigations of inhomogeneous and anisotropic magnetic field distribution.

Enhancement of Curie- and spin-spiral temperatures with doping Fe in multiferroic CoCr2O4 nanoparticles

Abstract Multiferroic, CoCr2O4 bulk material undergoes successive magnetic transitions such as paramagnetic to collinear ferrimagnetic state at Curie temperature (TC) and non-collinear spin-spiral ordering temperature TS followed by a lock-in-transition TL. In this paper, the rich sequence of magnetic transitions in CoCr2O4 nanoparticles after doping with iron ions are investigated by varying the concentration from x = 10 to 40%. With increasing iron concentration from 10 to 40%, while TC increases from 102 to 160 K higher than the TC of pure CoCr2O4, TS increases from 26 to 40 K. Later transition is clearly shown by sharp transition in specific heat measurement. While enhancement in TC is attributed to increase in lattice expansion and the exchange interaction between tetrahedral (A) and octahedral (B) sites, spin-spiral ordering is dictated by B-B interaction. Further, we have examined the magnetic transitions through neutron scattering using polarized neutron beam along three orthogonal directions. We observe that the para to ferrimagnetic transition is found to be continuous and the spiral ordering is diffused in nature irrespective of composition.

On Ternary Fission Induced by Neutrons

Experiments on measuring the rotational effect of the 234U fissile nucleus at the scission point showed that the fissile nucleus rotates as a right screw with respect to the longitudinally polarized neutron beam direction in the ternary fission of the 233U target nucleus induced by polarized s-neutrons; in the binary fission of the same nuclei it rotates in the opposite direction. Moreover, it was found that ternary fission “prefers” the spin state of J = I +1/2. This phenomenon cannot be explained within the existing concepts of ternary fission as one of the two “final” states after neck rupture. The same “parent” 234U nucleus cannot rotate in opposite directions in the two different final states. It should be assumed that ternary fission is a special branch of descent from the saddle point to the point of neck rupture. It can also be assumed that this branch is formed at the saddle point in a configuration favorable for cluster formation. Why does it prefer the spin state of J = I + 1/2? This is an interesting question for further studies.