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This manuscript describes a concept of a grazing incidence small-angle neutron scattering (GISANS) instrument for the high brilliance source (HBS). The HBS being a compact pulsed neutron source using a moderate energy proton accelerator which allows for very compact moderators and shielding, and flexible pulse repetition rates. Similar to many other instrument concepts for this source, the lowest proposed HBS pulse frequency of 24 Hz with a relatively large detector distance is the optimal choice for the instrument described here in terms of obtained intensity and Q-range (i.e. scattering vector range). Such a configuration has the added advantage of good Q-resolution, which is important when scattering depths need to be resolved well. This is especially the case for GISANS when the incident angle is close to the critical angle of total reflection. The performance obtained from detailed ray-tracing computer simulations predict a high performance instrument that will be comparable to reflectometers and small angle neutron scattering (SANS) instruments at high-flux reactor sources such as the Forschungsreaktor Munich (FRM-2) and others.

We investigate the spin rotational structure of magnetic skyrmions in a tetragonal polar magnet VOSe2O5 via polarized small-angle neutron scattering (SANS). Spin polarization analysis of the scattered neutrons provides consistent evidence for the cycloidal spin modulation in all the incommensurate phases at zero and non-zero magnetic field along the c axis, including the triangular skyrmion-lattice phase. In the vicinity of the skyrmion phase, we performed extensive SANS measurements to unravel a field-induced incommensurate phase (IC-2 state). We discuss the possibility of anisotropic double-q state as an alternative spin structure to provisional square skyrmion-lattice state., 27 pages, 5 figures

We report results of a new technique to measure the electric dipole moment of $^{129}\mathrm{Xe}$ with $^{3}\mathrm{He}$ comagnetometry. Both species are polarized using spin-exchange optical pumping, transferred to a measurement cell, and transported into a magnetically shielded room, where SQUID magnetometers detect free precession in applied electric and magnetic fields. The result from a one week measurement campaign in 2017 and a 2.5 week campaign in 2018, combined with detailed study of systematic effects, is ${d}_{A}(^{129}\mathrm{Xe})=(1.4\ifmmode\pm\else\textpm\fi{}6.{6}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}2.{0}_{\mathrm{syst}})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}28}\text{ }\text{ }e\text{ }\mathrm{cm}$. This corresponds to an upper limit of $|{d}_{A}(^{129}\mathrm{Xe})|l1.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}27}\text{ }\text{ }e\text{ }\mathrm{cm}$ (95% C.L.), a factor of 5 more sensitive than the limit set in 2001.

Low gradient magnetic holding fields are required for maintaining the polarization of polarized 3He, as diffusion though non-ideal gradients can cause total relaxation rates much greater than the intrinsic total 3He relaxation rate of a particular 3He cell in optimal conditions. For neutron scattering applications we often rely on µ-metal cavities to provide a degree of shielding from the many other sources of magnetic fields and gradient experienced on a typical neutron instrument. The JCNS utilizes two concepts for such cavities, one based on inexpensive plastic-bonded magnets to provide magnetic flux, and the other based on field coils wound on the sides of the µ-metal cavity. 2 different sized of permanent magnet cavities and three different geometries of coil-based cavities have been produced. Both types of boxes will be presented with magnetic design as well as mechanical construction details along with the achieved performance of the constructed devices.

12th International Conference on Polarised Neutrons for Condensed Matter Investigations, PNCMI 2018, Abingdon, UK, 3 Jul 2018 - 6 Jul 2018; Journal of physics / Conference Series 1316, 012009 (2019). doi:10.1088/1742-6596/1316/1/012009 special issue: "12th International Conference on Polarised Neutrons for Condensed Matter Investigations (PNCMI 2018) 3-6 July 2018, Abingdon, UK", Published by IOP Publ., Bristol

The spin-lattice relaxation time T1 of hyperpolarized (HP)-(129)Xe was improved at typical storage conditions (i.e. low and homogeneous magnetic fields). Very long wall relaxation times T(1)(wall) of about 18 h were observed in uncoated, spherical GE180 glass cells of ∅=10 cm which were free of rubidium and not permanently sealed but attached to a standard glass stopcock. An "aging" process of the wall relaxation was identified by repeating measurements on the same cell. This effect could be easily removed by repeating the initial cleaning procedure. In this way, a constant wall relaxation was ensured. The Xe nuclear spin-relaxation rate 1/T1(Xe-Xe) due to van der Waals molecules was investigated too, by admixing three different buffer gases (N(2), SF(6) and CO(2)). Especially CO(2) exhibited an unexpected high efficiency (r) in shortening the lifetime of the Xe-Xe dimers and hence prolonging the total T1 relaxation even further. These measurements also yielded an improved accuracy for the van der Waals relaxation for pure Xe (with 85% (129)Xe) of T(1)(Xe-Xe)=(4.6±0.1)h. Repeating the measurements with HP (129)Xe in natural abundance in mixtures with SF6, a strong dependence of T(1)(Xe-Xe) and r on the isotopic enrichment was observed, uncovering a shorter T(1)(Xe-Xe) relaxation for the (129)Xe in natural composition as compared to the 85% isotopically enriched gas.

An XYZ polarization analysis solution has been developed for the new thermal time-of-flight spectrometer TOPAS [1], to be operated in the coming east neutron guide hall at the MLZ. This prototype is currently being prepared to use on NEAT at HZB [2]. Polarization Analysis Studies on a Thermal Inelastic Spectrometer, commonly called PASTIS [3], is based on polarized 3He neutron spin filters and an XYZ field configuration for the sample environment and a polarization-preserving neutron guide field. The complete system was designed to provide adiabatic transport of the neutron polarization to the sample position on TOPAS while maintaining the homogeneity of the XYZ field. This complete system has now been tested on the polarized time-of-flight ESS test beam line V20 at HZB [4]. We present results of this test and the next steps forward.

The KWS-1 small-angle neutron scattering (SANS) instrument operated by the Jülich Centre for Neutron Science (JCNS) at the research reactor FRM II of the Heinz Maier-Leibnitz Zentrum in Garching near Munich has been recently upgraded. The KWS-1 instrument was updated, from its active collimation apertures to the detector cabling. Most of the parts of the instrument were installed for the first time, including a broadband polarizer, a large-cross-section radio-frequency spin flipper, a chopper and neutron lenses. A custom-designed hexapod in the sample position allows heavy loads and precise sample positioning in the beam for conventional SANS experiments as well as for grazing-incidence SANS under applied magnetic field. With the foreseenin situpolarization analysis the main scientific topic of the instrument tends towards magnetism. The performance of the polarizer and flipper was checked with a polarized3He cell at the sample position. The results of these checks and a comparison of test measurements on a ferrofluid in a magnetic field with polarized and nonpolarized neutrons are presented.

Fully polarized neutron reflectometry and grazing incidence small angle neutron scattering are effective methods to explore magnetic structures on the nm to μm length scales. This paper is an outline of how to fully correct for the polarization analysis (PA) inefficiencies of such an instrument and to determine the error contributions of the neutron polarizer and analyzer. This discussion considers the exact case of the polarization analysis instrumentation used on the MARIA neutron reflectometer at the MLZ or for a general polarized neutron scattering instrument using at least one 3He neutron spin filter that has the capability for adiabatic fast passage nuclear magnetic resonance flipping of the 3He polarization. This paper will work to build a conceptual understanding of how the inefficiencies of neutron polarization elements affect measured data in order to stress and encourage the application of PA corrections and to help perform successful measurements. Then, using data from a fully polarized neutron reflectometer test measurement we show how it is possible to recover signals on the order of, or even smaller than, the inefficiencies, or bleed-through, of the neutron polarization devices used.

We present an ultra-compact 3He polarizer to be used as a polarization analyzer for separation of incoherent background for soft matter research. The 3He will be polarized in-situ within a very compact, 18 cm long, magnetic cavity that can be placed between the sample and the detector tank of small-angle scattering diffractometer KWS2 at MLZ [1]. This allows for the angular coverage of 38°, that corresponds to the maximal momentum transfer Qmaxλ=0.85 Å−1 for neutrons with wavelength λ=4.5Å. The Qmax can be extended to 1.28 Å−1 following the recent upgrade of KWS2 for neutron wavelength λ=3Å. The optical pumping will be done by the diode laser array bar frequency narrowed by the ultra-compact volume Bragg grating. The full system will be readily hand transportable and thus useful as an instrument add-on.

et al., The combination of lithography and ion implantation is demonstrated to be a suitable method to prepare lateral multilayers. A laterally, compositionally, and magnetically modulated microscale pattern consisting of alternating Co (1.6 µm wide) and Co-CoO (2.4 µm wide) lines has been obtained by oxygen ion implantation into a lithographically masked Au-sandwiched Co thin film. Magnetoresistance along the lines (i.e., current and applied magnetic field are parallel to the lines) reveals an effective positive giant magnetoresistance (GMR) behavior at room temperature. Conversely, anisotropic magnetoresistance and GMR contributions are distinguished at low temperature (i.e., 10 K) since the O-implanted areas become exchange coupled. This planar GMR is principally ascribed to the spatial modulation of coercivity in a spring-magnet-type configuration, which results in 180° Néel extrinsic domain walls at the Co/Co-CoO interfaces. The versatility, in terms of pattern size, morphology, and composition adjustment, of this method offers a unique route to fabricate planar systems for, among others, spintronic research and applications., This work was financed by the Research Foundation-Flanders (FWO), the Concerted Research ActionGOA/14/007, the 2014-SGR-1015 project of the Generalitat de Catalunya, and the European Commission under the 7th Framework Programme through the “Research Infrastructure” action of the “Capacities” Programme, NMI3-II Grant No. 283883. This work is based upon experiments (Proposal Nos. 5928 and 9384) performed at the MARIA instrument operated by JCNS at Heinz Maier-Leibnitz Zentrum (MLZ), Garching, Germany. The authors would like to thank IMEC for access to its lithography facilities as well as J. Moonens and J. Loo for technical support. ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295).

This article describes a high-efficiency transmission polarizer that has been installed at the high-intensity SANS diffractometer KWS2 of the Julich Centre for Neutron Science. The polarizer is primarily designed to be used in the low resolution/high Q-range mode of this diffractometer for the purpose of the separation of coherent scattering on biological objects from an intrinsic background caused by incoherent scattering on their hydrogen atoms. The polarizer operates with a rather divergent incident beam and is placed at about 2m from the sample (upstream in the beam). The diffuse spin-flip scattering that would become critical for such geometry is suppressed due to the use of a strong, about 0.14T, magnetic field. The polarizer has been characterized by a 3 He neutron spin filter and provides very high polarization - 93% at 4.5 A and 99.7% for neutrons with wavelength above 6 A – for the SANS collimation 4m. The polarizer transmission at 4.5 A amounts to 94% of the desired spin component. The polarizer is placed in the collimation base of the instrument and can be easily put in and out of the beam thus allowing for “an instant” switch between polarized and non-polarized neutron beams.

Polarized neutron instruments will occupy about 80% of the Julich Centre for Neutron Science (JCNS) instrument park. A successful polarized 3He program will be integral to many of these instruments. We have been focusing the developments on spin-exchange optical pumping (SEOP) to polarize the 3He gas in situ. Where possible, in situ polarization using the SEOP method will provide higher time averaged performance of the instruments. Further this allows a custom-built and independent source of polarized 3He to be developed optimized for each instruments demands. In this paper we will: present an argument for the advantages of in situ polarization; describe an in situ polarizer we have constructed, and initial tests of its performance; describe testing of polarization analysis for small angle neutron scattering on biological samples, and our plans for an in situ polarizer for this application.

Maintaining high levels of 3 He polarization over long periods of time is important for many areas of fundamental and particle beam physics. Long measurement times are often required in such experiments, and the data quality is a function of the 3 He polarization. This is the case for neutron scattering, where the 3 He can be used to analyze the spin of a scattered neutron beam. For neutron scattering, the relatively small fluxes of polarized neutrons lead to experiment times longer than several days. Consequently, the Julich Centre for Neutron Science (JCNS) is developing spin-exchange optical pumping (SEOP) systems capable of polarizing the 3 He gas in place on a typical neutron instrument. With the polarizer we have constructed, a very high level of 3 He polarization of 80.4%±1.5% was obtained and maintained with good time stability. Having such high levels of polarization that are stable over time will reduce the measurement times for such experiments and eliminate time-dependent data corrections.

Polarized 3He has shown its unique characteristics in many areas of polarized neutron scattering, its ability to polarize neutrons at short wavelengths, accept wide-angle and divergent beams and low backgrounds enable new classes of experiments. While polarized 3He is not a steady state solution as commonly applied, the benefits have been shown to offset the drawbacks of polarizing and refreshing the polarization in the neutron spin filter cells. As an extension of this work, in-situ polarization using the spin-exchange optical pumping (SEOP) method was explored as a means to construct a system which could be used to polarize 3He in the state used for an effective neutron spin filter to constant polarization while on the neutron beam. An in-situ SEOP polarizer was constructed. This device utilized many devices and principles developed for neutron spin filters which are polarized off the beam line using either SEOP or metastability exchange optical pumping (MEOP) under the same research program. As a collimation of this work effects of extremely high neutron capture flux density > 1 × 10 10 cm - 2 s - 1 incident on the in-situ polarizer were explored.

We discuss the development and characterisation of a new in situ spin exchange optical pumping (SEOP) based 3 He neutron spin filter polarisation device. We present results from a recent test of the prototype system developed with the Institut Laue-Langevin. The polariser was installed on the polarised reflectometer CRISP at ISIS in the analyser position. The 3 He was pumped continuously in situ on the beamline. The system also integrated a 3 He adiabatic fast passage spin flipper that allowed reversal of the 3 He and therefore neutron polarisation state, allowing for measurement of all four polarisation cross-sections. The system was run for a number of days reaching a 3 He polarisation of 63%.

We present a detailed investigation into 3 He neutron spin filter cells polarised by spin exchange optical pumping (SEOP). We include measurements of the absolute 3 He polarisation using neutron transmission and characterisation of both the X -factor and 3 He relaxation times ( T 1 ) for a number of cells. For one cell we calculated a maximum 3 He polarisation of 79% with a T 1 of 633 h. The measured X -factor of this cell, X = 0.17 ± 0.01 , is low. For all cells polarisations of > 71 % are observed. In addition we present 3 He relaxation data for a new design of magneto-static cavity with a field of high homogeneity Δ B / B 0 ≈ 3.5 × 10 - 4 cm - 1 . This compact device provides a magnetic field in an orientation suitable for in situ optical pumping that minimises the field inhomogeneity contribution to the T 1 to 930 h in a 1 bar cell, the longest reported on beam thus far. The results suggest that high 3 He polarisation with long relaxation times can now be routinely obtained with SEOP, enabling time independent incident beam polarisation to be easily implemented across many different neutron scattering instruments.

We describe the development of a polarized neutron device that combines a 3 He neutron spin filter and a neutron spin flipper using adiabatic fast passage (AFP), to adiabatically reverse the 3 He polarization and thus the neutron polarization with near perfect symmetry. A typical AFP sequence takes place in 2.5–7.5 ms, with the time for the 3 He transition from P to - P much less, thus the neutron polarization is nearly perfectly reversed very quickly with only a 2 × 10 - 5 loss in 3 He polarization per flip. We believe this device, the 3 He “flipperizer” can become a standard option wherever a 3 He spin filter is already in use. Our first on beam test was performed on MIRA at the new FRM-2 reactor in Garching using polarized 3 He from HELIOS. We also briefly describe tests of a new neutron flipper based on AFP. This broad band neutron RF flipper was shown to create neutron flipping efficiencies of > 99 % at a neutron wavelength of 0.4 A. Neutron tests were performed on D3 (ILL) and on ROTAX (ISIS).

We present the results of measurements taken with the newly constructed PASTIS coil set insert, which uses a wide-angle “banana” 3He neutron spin-filter cell to cover a large range of scattering angles. The neutron polarization direction is freely rotatable to allow 3-directional (XYZ) polarization analysis and the coil set is designed to fit within the sample areas of most of the spectrometers at the Institut Laue-Langevin (ILL) in Grenoble. No significant depolarization due to the repeated spin rotations is observed. The PASTIS insert is now available for use on selected instruments at the ILL. This will enable XYZ neutron polarization analysis studies to be implemented on the majority of public ILL instruments.

We report progress in the development and application of neutron spin filters based on transmission through polarized 3 He gas. Tests and application of these devices are underway at the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) and the Intense Pulsed Neutron Source (IPNS). The results of application to polarization analysis for diffuse reflectometry is discussed, along with an example of the issues in choosing the flipping ratio for such applications. The status of our development of polarized gas production using both spin-exchange (SEOP) and metastability-exchange (MEOP) optical pumping will be presented. For SEOP, we currently obtain 70–75% 3 He polarization in cells up to 500 cm 3 in volume.

© 2015 Owned by the authors, published by EDP Sciences. We report on the progress of the construction of the thermal time-of-flight spectrometer with polarization analysis TOPAS at the Mayer-Leibnitz Zentrum (MLZ). The instrument components approach the status to be ready for installation. The special feature of the instrument is its capability for wide-angle polarization analysis in the thermal spectral range. Here we describe a novel approach to rotate the neutron spin adiabatically into the X, Y or Z direction of the laboratory frame by combination of permanent magnets aligned as Halbach rings and electrically generated fields. Despite the severe spatial restrictions the design exhibits a very high adiabaticity and interacts only weakly with the coil layout for the analyzing 3He spin filter cell (SFC).

We describe here a method of performing adiabatic fast passage (AFP) spin flipping of polarized 3 He used as a neutron spin filter (NSF) to polarize neutron beams. By reversing the spin states of the 3 He nuclei the polarization of a neutron beam can be efficiently reversed allowing for the transmission of a neutron beam polarized in either spin state. Using an amplitude modulated frequency sweep lasting 500 ms we can spin flip a polarized 3 He neutron spin filter with only 1.8×10 −5 loss in 3 He polarization. The small magnetic fields (10–15 G) used to house neutron spin filters mean the 3 He resonant frequencies are low enough to be generated using a computer with a digital I/O card. The versatility of this systems allows AFP to be performed on any beamline or in any laboratory using 3 He neutron spin filters and polarization losses can be minimised by adjusting sweep parameters.

Polarized 3 He spin-filters are currently employed on a wide range of neutron instruments at the ILL, primarily for diffraction, reflectometry and fundamental physics. A wide range of recent and ongoing improvements are enabling the implementation of this technique for wide-angle polarization analysis for inelastic measurements. These include • Progress in metastability-exchange optical pumping (MEOP), resulting in on-beam polarization levels of up to 80%. • 1st generation “Pastis-1” coils for rotating the neutron polarization at the sample position, allowing for “ XYZ ” polarization analysis. • 2nd generation “Pastis-2” coils with no blind angles in the equatorial plane. • Spin-filter cells with glued silicon windows, allowing for wide-angle “banana” cells with very low background scattering. • Polarization-preserving capillaries for transferring polarized 3 He gas into the cell without manual access. The development of capillary transfer also allows for a completely new way of working with 3 He spin-filters: connecting the cells on the instruments directly to the MEOP filling station several tens of meters away and allowing for quasi-continuous operation.

We discuss the use of a new test beamline on the ISIS time-of-flight neutron source where the pressure, polarisation and relaxation time of spin-polarised 3He neutron spin filter (NSF) cells can be determined. The beamline consists of a 3He cell held in a magnetostatic cavity and a 3He monitor in which the change in neutron transmission due to the highly spin-dependent cross-section of 3He is measured. The neutron polarisation is simultaneously confirmed using the asymmetry method, through the use of a Heusler crystal analyser and Mezei flipper. The beamline is routinely used in the characterisation of 3He (NSF) cells and polarisations of up to 70% in sealed spin exchange optically pumped cells have been measured using both techniques.

We report the present status and recent advances made in polarised- 3 He spin-filters at the ILL. The Tyrex filling station is working reliably and producing polarised 3 He for neutron spin filters on a daily basis. The latest spin-filter cells have wall relaxation times between 200 and 400 h — the longest relaxation times yet achieved for valve-sealed cells. Recent results using 3 He spin filters for reflectometry are presented and compared to the presently used supermirror-based polarisation analysers. By increasing the optical thickness of 3 He gas, we move into a regime in which the neutron beam polarisation decays with a time constant of the order of a thousand hours and is thus negligible within the 24 h time scale of an experiment. We present the performance of a 3 He spin flipper, which inverts the polarisation direction of the 3 He nuclei by adiabatic fast passage with a polarisation loss of 10 −5 per flip. The development of in situ filling of the spin-filter cell via a capillary is described. This “local filling” technique enables 3 He spin filters to be used in inaccessible regions, such as inside large-detector vacuum tanks and in high-radiation environments.

A versatile and portable magnetically shielded room with a field of (700 \pm 200) pT within a central volume of 1m x 1m x 1m and a field gradient less than 300 pT/m is described. This performance represents more than a hundred-fold improvement of the state of the art for a two-layer magnetic shield and provides an environment suitable for a next generation of precision experiments in fundamental physics at low energies; in particular, searches for electric dipole moments of fundamental systems and tests of Lorentz-invariance based on spin-precession experiments. Studies of the residual fields and their sources enable improved design of future ultra-low gradient environments and experimental apparatus. A versatile and portable magnetically shielded room with a field of (700 ± 200) pT within a central volume of 1 m × 1 m × 1 m and a field gradient less than 300 pT/m, achieved without any external field stabilization or compensation, is described. This performance represents more than a hundredfold improvement of the state of the art for a two-layer magnetic shield and provides an environment suitable for a next generation of precision experiments in fundamental physics at low energies; in particular, searches for electric dipole moments of fundamental systems and tests of Lorentz-invariance based on spin-precession experiments. Studies of the residual fields and their sources enable improved design of future ultra-low gradient environments and experimental apparatus. This has implications for developments of magnetometry beyond the femto-Tesla scale in, for example, biomagnetism, geosciences, and security applications and in general low-field nuclear magnetic resonance (NMR) measurements. A versatile and portable magnetically shielded room with a field of (700 \pm 200) pT within a central volume of 1m x 1m x 1m and a field gradient less than 300 pT/m is described. This performance represents more than a hundred-fold improvement of the state of the art for a two-layer magnetic shield and provides an environment suitable for a next generation of precision experiments in fundamental physics at low energies; in particular, searches for electric dipole moments of fundamental systems and tests of Lorentz-invariance based on spin-precession experiments. Studies of the residual fields and their sources enable improved design of future ultra-low gradient environments and experimental apparatus.

Over the past several years the JCNS has been developing in-house applications for neutron polarization analysis (PA). These methods include PA for separation of incoherent from coherent scattering in soft matter studies (SANS), and online polarization for analysis for neutron reflectometry, SANS, GISANS and eventually spectroscopy. This paper will present an overview of the user activities at the JCNS at the MLZ and gives an overview of the polarization 3He methods and devices used. Additionally we will summarise current projects which will further support the user activities using polarised 3He spin filters.

We report on the first results of the newly proposed and prototyped PASTIS coil set, enabling for XYZ polarization analysis on the future thermal time-of flight spectrometers. Our setup uses a wide-angle banana shaped 3He Neutron Spin Filter cell (NSF) to cover a large range of scattering solid angle. The design assures relative magnetic field gradients < 10-3 cm-1 and large solid angle areas not interrupted by either coils or supports. In the vertical direction nearly 40° are open and the blind spots in the horizontal scattering plane comprise only 3° in 180° due to the square X and Y compensation coils. We present the first results of the field mapping and relaxations time measurements using a large 3He SEOP polarized GE180 doughnut cell.

Polarization analysis is an important technique for polarized neutron scattering as it allows one to obtain the full information about the vector magnetization in the sample that is critically important for detailed understanding of physical properties of molecular magnets, new superconductors, spin electronic and magnetic nanostructures, as well as the self-organization of magnetic nanostructures. In the simplified 1-dimensional version polarization analysis allows for the separation of coherent and incoherent scattering, making it a potentially important technique for studies of non-deuterated biological objects that themselves produce unavoidable background. We compare some of the major considerations between two different methods for the polarization analysis – supermirror based analyzers and polarized 3He neutron spin filters and point out when the latter is beneficial from the point of view of our neutron experiments and instrumentation. We will also discuss some specific requirements to such neutron spin filters and summarize the classes of instrumentation where they will be applied at the JCNS. Finally we will describe a successful application for small-angle neutron scattering from a biological sample.

We present measurements, by using two complementary methods, of the breakdown of atomic angular momentum selection rules in He-broadened Rb vapor. Atomic dark states are rendered weakly absorbing due to fine-structure mixing during Rb-He collisions. The effect substantially increases the photon demand for optical pumping of dense vapors.

We present measurements of the circular dichroism of optically pumped Rb vapor near the ${D}_{1}$ resonance line. Collisions with the buffer gases $^{3}\mathrm{He}$ and ${\mathrm{N}}_{2}$ reduce the transparency of the vapor, even when fully polarized. We use two methods to measure this effect, show that the He results can be understood from RbHe potential curves, and show how this effect conspires with the spectral profile of the optical pumping light to increase the laser power demands for optical pumping of very optically thick samples.

We present the design for the polarization analysis of the future thermal time-of-flight spectrometer at the Juelich Centre for Neutron Science (JCNS) at the FRM II. TOPAS is a time-of-flight spectrometer covering a range of incident energies 20 meV < Ei < 160 meV and an angular range −3° < 2θ < 150°. A set of Fermi choppers selects the incoming energy Ei with a resolution up to 3 %. The instrument is optimized for a high flux on small samples using an elliptical neutron guide. The special feature of TOPAS is the polarization analysis. The incident polarization will be realized by means of a 3He continuously pumped polarizer, which is a downscaled version of the device developed for small angle applications at JCNS. The polarization analysis over a wide angular range demands either short distances between the sample and the analyzer or a large volume of polarized 3He. Here we propose the latter alternative to allow the study of magnetic samples and modest magnetic fields at the sample position.

Polarized $^{3}\text{H}\text{e}$ produced by spin-exchange optical pumping (SEOP) has potential as a neutron spin filter for polarization and polarization analysis in many neutron-scattering and neutron particle physics applications. The advantage of the SEOP method is its suitability for providing continuous stable polarization over the course of long experiments. However, we have discovered that exposure to high neutron flux leads to additional strong relaxation mechanisms in the optically polarized alkali-metal vapor used to polarize the $^{3}\text{H}\text{e}$. At a neutron flux density of $4.7\ifmmode\times\else\texttimes\fi{}{10}^{9}\text{ }{\text{cm}}^{\ensuremath{-}2}\text{ }{\text{s}}^{\ensuremath{-}1}$, the alkali-metal relaxation rate increased from 100 to $1000\text{ }{\text{s}}^{\ensuremath{-}1}$ leading to reduced alkali-metal polarization. Other effects such as time dependence and gas composition dependence were explored to help understand the processes. In this paper we discuss our observations and present possible solutions for practical use of SEOP as a neutron spin filter for high-flux density applications.

We have observed depolarization effects when high intensity cold neutron beams are incident on alkali-metal-spin-exchange polarized He-3 cells used as neutron spin filters. This was first observed as a reduction of the maximum attainable He-3 polarization and was attributed to a decrease of alkali-metal polarization, which led us to directly measure alkali-metal polarization and spin relaxation over a range of neutron fluxes at LANSCE and ILL. The data reveal a new alkali-metal spin-relaxation mechanism that approximately scales as the square root of the neutron capture-flux density incident on the cell. This is consistent with an effect proportional to the recombination-limited ion concentration, but is much larger than expected from earlier work., submitted to Physical Review Letters

We have studied the efficiency of spin-exchange optical pumping SEOP in cells that contain either pure rubidium, mixtures of rubidium and potassium, or pure potassium. Optical pumping was performed with spectrally narrowed diode array lasers operating at either the wavelength of the Rb 5s1/2-5p1/2 transition 795 nm or the K 4s1/2-4p1/2 transition 770 nm. Calculations of the expected efficiency are shown for practical conditions and compared to measurements. We have measured the vapor density ratio in Rb-K mixture cells using absorption of white light. Our focus is on the conditions that are relevant for neutron spin filters, but the results are relevant to all applications of SEOP. We find that both Rb-K and pure K cells yield improvements in the spin-exchange efficiency, and each approach has its own advantages. Overall, the best results for high polarizing rate with high polarization were obtained with mixture cells with K-Rb vapor density ratios between 2 and 6.

We present temperature-dependent measurements of the EPR frequency shifts for Na, K, and Rb interacting with polarized $^{3}\mathrm{He}$. K and Na frequency shifts were measured via comparison with Rb frequency shifts (well known at low temperatures) in $\mathrm{Na}\ensuremath{-}\mathrm{Rb}\ensuremath{-}^{3}\mathrm{He}$ and $\mathrm{K}\ensuremath{-}\mathrm{Rb}\ensuremath{-}^{3}\mathrm{He}$ spin-exchange cells. The lowered Rb vapor pressure of these ``hybrid'' spin-exchange cells also allowed us to extend the measured temperature dependence of the Rb EPR frequency shifts up to $350\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. This work presents measurements of the EPR frequency shift for Na in $^{3}\mathrm{He}$ and significantly extends the temperature range of previous Rb and K EPR frequency shift measurements. These results are critical to the performance of accurate $^{3}\mathrm{He}$ EPR polarimetry in spin-exchange cells.

We demonstrate spin-exchange optical pumping of 3He using a "hybrid" K-Rb vapor mixture. The Rb atoms absorb light from a standard laser at 795 nm, then collisionally polarize the potassium atoms. Spin-exchange collisions of K and 3He atoms then transfer the angular momentum to the 3He with much greater efficiency than Rb-3He. For a K-rich vapor, the efficiency of the hybrid spin-exchange collisions approaches 1/4, an order of magnitude greater than achieved by pure Rb pumping. We present the first measurements of actual photon efficiencies (polarized nuclei produced per absorbed photon), and show that a new parasitic absorption process limits the total efficiencies for both hybrid and pure Rb pumping.

We demonstrate spin-exchange optical pumping of 3He using a "hybrid" K-Rb vapor mixture. The Rb atoms absorb light from a standard laser at 795 nm, then collisionally polarize the potassium atoms. Spin-exchange collisions of K and 3He atoms then transfer the angular momentum to the 3He with much greater efficiency than Rb-3He. For a K-rich vapor, the efficiency of the hybrid spin-exchange collisions approaches 1/4, an order of magnitude greater than achieved by pure Rb pumping. We present the first measurements of actual photon efficiencies (polarized nuclei produced per absorbed photon), and show that a new parasitic absorption process limits the total efficiencies for both hybrid and pure Rb pumping.

He. In the course of these measurements we developed and tested a new method for Rb densitymeasurements under high power pumping conditions, and a new variant of Rb EPR polarimetry, both of whichare described here.DOI: 10.1103/PhysRevA.66.032703 PACS number~s!: 34.30.1h, 32.80.Bx, 33.25.1kI. INTRODUCTION

In order to produce high-quality 3He Neutron Spin Filters (NSF) with a high polarisation level, it is necessary to achieve a long 3He relaxation time by the reduction of the wall relaxation. This requires one to minimise the amount of impurities at the surface of the glass cells, and to have as few contaminants as possible in the gas filling system. In this report we describe the detailed procedure we employ to produce 3He cells using our newly built filling station. The obtained life times for a number of cells are practically approaching the fundamental limit imposed by the dipole-dipole interaction between 3He atoms.

We present progress towards a complete system for neutron polarization analysis on a time-of-flight (TOF) neutron spectrometer with a large area/angle detector array. Finite element calculations have been used to model the field gradients of a newly proposed PASTIS coil set, which uses a wide-angle banana shaped 3He Neutron Spin Filter cell (NSF) to cover a large neutron scattering solid angle. The final goal of this insert is to enable X-Y-Z polarization analysis to be installed on the future hot/thermal time-of flight spectrometers, although the method is also applicable to thermal/cold spectrometers as well. The components of this system, such as the magnetic field coils and design are applicable to neutron spectroscopy with wide angle detector arrays in general, and the 3He wide angle cell developments for polarized inelastic neutron scattering are independent from the methods used to polarize the gas as well.

We have obtained improvement in the 3He polarization achievable by spin-exchange optical pumping (SEOP). These results were primarily obtained in large neutron spin filter cells using diode bar lasers spectrally narrowed with chirped volume holographic gratings. As compared to our past results with lasers narrowed with diffraction gratings, we have observed between 5% and 11% fractional increase in the 3He polarization P He. We also report a comparable improvement in P He for two small cells, for which we would not have expected an increase from improved laser performance. In particular, prior extensive studies had indicated that the alkali-metal polarization was within 3% of unity in one of these cells. These results have impact on understanding the maximum P He achievable by SEOP, whether the origin of the improvement is from increased alkali-metal polarization or decreased temperature-dependent relaxation. We conclude that the most likely explanation for the improvement in P He is increased alkali-metal polarization. We have observed P He of between 0.80 and 0.85 in several large cells, which marks a new precedent for the polarization achievable by SEOP.

Polarization analysis will be needed on modern neutron scattering instrumentation designed to measure wide dynamic Q-ranges. These instruments will often use large area detectors and potentially multiple neutron wavelength bands or pulsed sources. This will place high demands on the method used for the polarization analysis. Two methods, super mirrors and 3He neutron spin filters, are often considered as the only solutions. In this paper we will discuss the basic differences in these two methods for applications measuring a wide dynamic Q-range via the use of large area detectors. First we will present the simplified theory for conceptual understanding of how both wide angle SM and wide angle 3He analyzer devices perform. Then we discuss how the properties of each method will effect neutron performance taking into account practical considerations. Such a conceptual understanding of the basics of design, performance and limitations of the two main options for such wide angle polarization analysis is timely...

Prior studies revealed neutron beam-induced alkali-metal spin relaxation in 3He cells polarized in-situ by spin-exchange optical pumping. These effects are minor for neutron beams of low to moderate intensity, but become important at the highest neutron flux levels available in the full spectrum beams of high flux neutron sources. It was found that the relaxation consisted of a fast and a slow component, but the origin of neither is understood. This work further explored the mechanisms of this effect by measuring the magnitude and time dependence of alkali-metal spin-relaxation rates as a function of N2 and 3He composition. The experiments were performed on a thermal neutron beam line at the Institut Laue-Langevin with a maximum neutron flux of 2.4 × 109 cm−2 s−1.

The Julich Centre for Neutron Science is developing spin-exchange optical pumping systems capable of polarizing the 3He gas for use as neutron spin filters with developments focused on individually optimized solutions for each application. When possible steady polarization achieved with in-situ optical pumping will provide high time averaged neutron performance and time-stability, however some applications are foreseen to use a "local filling station" approach. In-situ polarizers are being developed for polarization analysis on reflectometry and small angle neutron scattering instruments. This overview of the current status of our SEOP program describes the motivation of in-situ polarization, the design and first results from the polarizer for analysis on reflectometry, and discusses the designs for a SANS analyzer and plans for wide angle analysis.

Polarized neutron scattering techniques are an indispensable and highly requested tool for studying magnetic phenomena in condensed matter. The different coherent and incoherent scattering of isotopes such as protons and deuterons also allows applications of polarized neutrons in soft matter and biological studies of molecular and macromolecular dynamics. One method to polarize neutrons is to use polarized 3He gas which absorbs, or filters, one spin state of the neutron beam as it passes through it. Only about ten years ago, early polarized neutron scattering experiments using such 3He neutron spin filters (3He NSF) were being conducted using starting 3He polarizations of 55%. Currently there are two different commonly used methods to polarize high quantities of 3He. These methods both collisionally transfer spin polarization to ground state 3He nucleuses; one method uses optical pumping of an excited metastable state of 3He atoms, and the other uses optical pumping of the ground state of an alkali-metal vapour. Within the last decade immense progress in both methods has resulted in 3He polarizations of up to 80% being reported in atmosphere-pressure 3He cells by the world's leading labs. This progress in optical pumped 3He promises to give rise to much more efficient and novel polarized neutron scattering experiments as and also impacts other areas of science. Polarized 3He is additionally applied in research fields such as particle physics, fundamental studies and medicine. Thus not only the techniques and methods of polarization, but the research groups themselves exploring polarized 3He, have a large breadth and diversity spanning different fields of science and locations in the world. Given this diversity, it is rare for this community to meet as a group at any one meeting or conference. Because it is crucial to discuss new developments in 3He polarization in a multi-disciplinary international setting, an international workshop on "Modern Trends in Production and Applications of Polarized 3He" was held from 11–13 July 2010 in Ismaning, Germany. This workshop was organized by the Julich Centre for Neutron Science (JCNS) as part of our ongoing series of topic-oriented JCNS workshops relating to specific activities of the JCNS. In particular this JCNS workshop discussed the techniques of polarization of 3He, 3He containers, magnetic holding systems, 3He spin manipulations and applications in neutron scattering, medicine and physics. The workshop was very well attended with intense discussions and inspiring presentations. In many ways the current workshop was a conceptual descendent of the HELION workshop in 2002 in Mainz, Germany. It is the hope of both us and many of the participants that such a workshop will be held again, perhaps 3 to 4 years in the future. The current proceedings is a collection of papers written within the spirit of the workshop to provide a documentation of the current status and perspectives in the polarization of 3He and its applications. Alexander IoffeEarl BabcockThomas GutberletEditors

We describe a method to frequency narrow multielement high-power diode bars. Using a commercial 60-W, 49-element, 1-cm-long diode array bar at 795 nm running at 45 W, we narrow the linewidth from 1000 to 64 GHz with only a loss of 33% in output power. The resulting laser light is well suited for spin-exchange optical pumping of noble gas nuclei.