Neutron multiwave spin echo

The neutron multiwave interference mode is investigated using the spin echo technique. In this mode a neutron wave repeatedly splits in the magnetic field of resonance coils, which results in the appearance of additional maxima of a constructive interference being absent in the well-known classical and resonance neutron spin echo modes. Simple analytical expressions well describing the experimental data are presented. It is demonstrated that the multiwave part of a spin echo signal appears when the spin flip probability in radiofrequency coils of a resonance spin echo device is ρ < 1. The possibility to use the neutron multiwave spin echo mode for investigation of high-order correlation functions, spatial and time correlations of three and more particles, is discussed.     

On polarized neutron scattering from magnetized samples and the spin echo effect

The scattering of polarized neutrons from magnetized samples is considered in the general case of arbitrary orientation between the incident polarization, the magnetic field of the sample and the polarization of the scattered neutrons. Including both nuclear and magnetic scattering the general expressions for the cross section and the polarization of the scattered beam are derived in the case of small-angle scattering. It is shown that under certain experimental conditions an effect analogous to the Neutron Spin Echo should be observed, which could be used to measure small energy transfers. The contribution arising from the scattering by spin waves is examined in detail.     

Challenges in neutron spin echo spectroscopy

With the new brilliant neutron sources and the developments of novel optical elements, neutron spin echo (NSE) spectroscopy evolves to tackle new problems and scientific fields. The new developments pave the way to complex experimental set-ups such as the intensity modulated variant of NSE (IMNSE), a powerful technique which was introduced some 20 years ago but found limited use up to now. With the new compact supermirror or He³ polarizers IMNSE becomes attractive for a broad range of applications in magnetism, soft matter and biology. A novel development along this line is the polarimetric NSE technique, which combines IMNSE and the zero-field polarimeter Cryopad to access components of the scattered polarization that are transverse to the incoming polarization. Polarimetric NSE is the method of choice for studying chiral fluctuations, as illustrated by new results on the reference helimagnet MnSi.     

中子自旋回波：研究蛋白质结构域动力学的利器

蛋白质作为生物系统这种复杂分子机器的重要组成部分之一,理解它们内部的结构及其在不同时间及空间尺度上的运动,对于研究生命的运作机理至关重要。相较于其他实验手段,中子自旋回波技术能探测到更大时空范围的性质,在研究蛋白质内部的结构域动力学方面具有独特的优势。这是一门横跨核物理与核技术、非平衡态统计物理学、分子生物学与蛋白质组学等前沿交叉领域的学科,充满着诸多未知与挑战,也遍布着一探生命奥秘的机遇。文章简述了中子自旋回波实验技术的基本原理和发展历程,阐述其在研究蛋白质结构域动力学方面的方法和技术优势,并介绍了部分实验案例,最后对其应用前景进行探讨与展望。     

A beam divergence correction mirror for neutron resonance spin echo

Neutron resonance spin echo (NRSE) enables us to measure neutron quasi-elastic scattering with high energy resolution. Its energy resolution is limited by a path length variation due to the beam divergence. Neutron focusing technique using a neutron supermirror can be used to overcome this problem. To investigate the effect of a cylindrical mirror on the path length variation due to the beam divergence, MIEZE (modulation of intensity by zero effort) spin echo measurement was performed. The result demonstrated that the cylindrical mirror effectively corrects the path length variation and leads to high energy resolution as well as high intensity in NRSE and MIEZE measurement.     

A wide angle neutron spin filter system using polarized He

Polarized ³He neutron spin filters can operate over a wide neutron energy range and provide a large angular acceptance. A compact ³He neutron spin filter system has been developed for the Multi-Axis Crystal Spectrometer at the National Institute of Standards and Technology (NIST) Center for Neutron Research. Sealed ³He cells, polarized by spin-exchange optical pumping, are used as polarizer and analyzer. The polarization of the neutrons incident on the sample is inverted by flipping the polarization of the ³He gas in the polarizer, with only a small effect on the analyzer cells. The cell fabrication process, ³He spin flipper, and the holding magnetic field are discussed and we present the results of a first on-linetest.     

Dynamics of polyrotaxane investigated by neutron spin echo

The dynamics of a molecular necklace known as polyrotaxane (PR), in which α-cyclodextrins (CDs) are threaded into a poly (ethylene glycol) (PEG) chain, was investigated by means of neutron spin echo (NSE) measurements. We observed that threading CDs into PEG slowed down the local dynamics and changed its Q-dependence. A solution of PEG in DMSO-d₆ showed a dynamical crossover from collective diffusion dynamics to the Zimm mode, just as in conventional polymer solutions; however, the motion of PR in DMSO-d₆ was diffusive for the whole Q range. This may be because the persistence length l_p of PR was much larger than that of PEG and was similar to the mesh size of PR. The diffusive mode in a high Q regime, corresponding to a length scale of less than the l_p value of PR, contained the mode of the sliding of CDs along a rod-like PEG segment in one dimension.     

A neutron resonance spin echo spectrometer for quasi-elastic and inelastic scattering

We propose a modified neutron spin echo (NSE) spectrometer using high frequency spin flippers to replace the static spin flipper and the long magnetic precession field in each arm of the classicalspin echo setup. The spectrometer is suitable for quasi-elastic as well as inelastic scattering and can work with an arbitrary magnetic field on the sample. The restrictions on sample size and scattering angle can be relaxed, in comparison with the classical NSE method.     

Spin-glass dynamics determined from muon spin relaxation and neutron spin echo measurements

Muon spin relaxation (SR) and neutron spin echo (NSE) measurements of magnetic ion correlation times and correlation functions in the spin glass systemsCuMn,AgMn, andAuFe are compared. It is found that theSR and NSE measurements are in excellent agreement both above and below the spin-glass freezing temperatures. The experimental results are compared to recent theories of spin-glass dynamics.We are grateful to D.L. Huber and R.E. Walstedt for stimulating discussions. This work was performed under the auspices of the U.S. Department of Energy, and was also supported by the U.S. National Science Foundation, Grant No. DMR-8115543.     

Development of neutron resonance spin flipper for high resolution spin echo spectrometer

A new type of neutron resonance spin flipper (RSF) with high frequency oscillating magnetic field has been developed for Modulated IntEnsity by Zero Effort (MIEZE) spectrometer at cold neutron beam line MINE1 at JRR-3M reactor in JAEA. Dipole magnets enable us to provide the strong static fields for the RSFs. MIEZE signals have been demonstrated with the effective frequency of 600 kHz by using the new RSFs. The contrast of the signals was 0.58. The MIEZE spectrometer is under final process to practical use. The spectrometers can also be applied to the pulsed neutrons like J-PARC.     

Birefringent neutron prisms for spin echo scattering angle measurement

In the first decade of the 19th century, an English chemist, William Wollaston, invented an arrangement of birefringent prisms that splits a beam of light into two spatially separated beams with orthogonal polarizations. We have constructed similar devices for neutrons using triangular cross-section solenoids and employed them for Spin Echo Scattering Angle Measurement (SESAME). A key difference between birefringent neutron prisms and their optical analogues is that it is hard to embed the former in a medium which has absolutely no birefringence because this implies the removal of all magnetic fields. We have overcome this problem by using the symmetry properties of the Wollaston neutron prisms and of the overall spin echo arrangement. These symmetries cause a cancellation of Larmor phase aberrations and provide robust coding of neutron scattering angles with simple equipment.     

Detector area expansion at iNSE neutron spin echo spectrometer

Expansion of a detection area is an effective method to increase the measurement efficiency of a neutron spin echo (NSE) spectrometer as well as other spectrometers. For this purpose, we installed a new π/2 spin flipper and Fresnel coil of iNSE spectrometer at JRR-3, Tokai, Japan, for wide-area data acquisition. In this study, we propose a data reduction method to correct the phase inhomogeneity due to the path difference of neutrons on the large detection area. This method can convert many NSE signals at small areas to one NSE signal at a large area with taking the phase offset due to the phase inhomogeneity into account. The measurement efficiency increased by approximately one order of magnitude as a result of the detection area expansion.     

Spatial spin resonance of polarized neutrons. A tunable slow neutron filter

The present paper is concerned with the physical properties of the phenomenon of spatial spin resonance (SSR) of polarized neutrons and its applications. The SU(2) group provides a mathematical tool for the theoretical discussion of SSR. The experimental work made use of the WWR-M reactor at the Leningrad Nuclear Physics Institute of the USSR Academy of Sciences.The theoretical analysis of SSR is based, in physical terms, on the concept of two distortion scales of the alternating magnetic field in the frame of reference of a moving neutron, playing the principal role in SSR. A period of the alternating magnetic field is adopted as a unit of scale. Large- scale distortions correspond to a region of the resonance spectrum in the vicinity of the principal resonance maximum, whereas small-scale distortions are mapped in zones away from this maximum.An analysis has enabled us to calculate and design resonators with which it is possible to act on specified parts of the resonance spectrum. These modified resonators are provided by the so-called “shaped meander” and “double meander” configuration, which permit the suppression of the subsidiary maxima and the high-order resonance spectrum. Some applications of these resonators are presented as devices for monochromatization of a polarized thermal neutron beam.     

Neutron thermometry on polarized silver nuclei at sub-microkelvin spin temperatures

We have utilized both neutron transmission and neutron diffraction to measure the spin polarization in a single crystal of ¹⁰⁹Ag, whereby the nuclear spin temperature could be obtained. Transmission of a polarized neutron beam provides an accurate and convenient primary thermometer. The feasibility of unpolarized neutron transmission was demonstrated as well. The diffraction measurements were strongly influenced by extinction, whence this method had to be calibrated against another thermometer. In this way we obtained information about extinction in the crystal.     

Ground state energy of spin polarized hard core neutron matter

The expansion of the ground state energy of spin polarized hard core neutron matter in powers of x =k_Fc (k_F = Fermi momentum, c = hardcoreradius) is calculated up to terms ≈x⁸.     

Microscopic calculations of spin polarized neutron matter at finite temperature

The properties of spin polarized neutron matter are studied both at zero and finite temperature within the framework of the Brueckner–Hartree–Fock formalism, using the Argonne v18 nucleon–nucleon interaction. The free energy, energy and entropy per particle are calculated for several values of the spin polarization, densities and temperatures together with the magnetic susceptibility of the system. The results show no indication of a ferromagnetic transition at any density and temperature.     

A spin polarized disc

We present a solution to the gravitational field equations in a Riemann-Cartan spacetime. The solution describes a disc of infinite radius and finite thickness. The solution has three forms which depend on the size of the acceleration. The matter content of the disc is a rotating spin fluid with a constant z acceleration and a spin density polarized along the axis of rotation. The fluid has zero axial and tangential pressures. There is a radial pressure. The energy density and pressure are finite within the disc.     

Advanced imaging techniques: A new deal for neutron physics

Among non-destructive evaluations and methodologies—the important set of analyses which preserve the integrity of the tested object—neutron imaging techniques, and neutron computerized tomography in particular, represent powerful tools. Although they have been considered more an amusement for scientists rather than an effective tool for engineers until few years ago, it can be stated that they can now provide valuable quantitative results in many circumstances of interest, being the only available choice in some specific cases. This wider interest and the attempt to give neutron imaging a certain prominence reflect themselves in the birth of an international group of people involved in the field of neutron research; the so-called ENRWG (European Neutron Radiography Working Group). Connected to a general interest and a diffuse curiosity in the fascinating interactive world of INTERNET there is also the possibility, since last year, to get information about neutron radiography state of the art and current projects from a free-access WWW site. As a consequence of these fervent activities, a new deal in studies of advanced materials, sources, detectors and algorithms is now growing to promote and to develop the capabilities of neutron imaging techniques after a long period during which the interest in neutron physics and in their applications was limited to selected specialists involved in the nuclear-energy production. The results of this effort will not be limited to improved technological processes, but will include an improved knowledge in relevant fields of nuclear and material science.