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A general theory is presented describing the photo-excitation dynamics of transient, paramagnetic triplet states of aromatic molecules including their absorption properties in a molecular host crystal when irradiated by a pulsed laser beam. It is applied to the system of a pentacene doped naphthalene single crystal, where the photo-excitation of pentacene results in a highly non-equilibrium population of intermediate electronic triplet states. These paramagnetic states can be addressed to align the proton spins of the naphthalene host at moderate experimental conditions using dynamic nuclear polarisation (DNP). The photo-excitation profile and the resulting triplet state distribution, which is determined by the material and the laser parameters, leads to a corresponding proton polarisation profile. Measurements of the resulting polarisation inhomogeneity by spatially resolved neutron transmission confirm the theory. The theoretical model then allows the extraction of crucial parameters that enable quantitative investigations of the dynamics of spin systems. For applications of triplet DNP with pentacene-doped naphthalene crystals, polarisation maximum, homogeneity and build-up rate are key factors, and the theory allows the identification of optimal experimental parameters depending on the priorities placed on these factors.

This paper presents a theory describing the dynamic nuclear polarization (DNP) process associated with an arbitrary frequency swept microwave pulse. The theory is utilized to explain the integrated solid effect (ISE) as well as the newly discovered stretched solid effect (SSE) and adiabatic solid effect (ASE). It is verified with experiments performed at 9.4 GHz (0.34 T) on single crystals of naphthalene doped with pentacene-d(14). It is shown that the SSE and ASE can be more efficient than the ISE. Furthermore, the theory predicts that the efficiency of the SSE improves at high magnetic fields, where the EPR line width is small compared to the nuclear Larmor frequency. In addition, we show that the ISE, SSE, and ASE are based on similar physical principles and we suggest definitions to distinguish among them.

Hyperpolarization of nuclear spins enhances nuclear magnetic resonance signals, which play a key role for imaging and spectroscopy in the natural and life sciences. This signal amplification unlocks previously inaccessible techniques, such as metabolic imaging of cancer cells. In this work, electron spins from the photoexcited triplet state of pentacene-doped naphthalene crystals are used to polarize surrounding protons. As existing strategies are rendered less effective by experimental constraints, they are replaced with optimal control pulses designed with RedCRAB. In contrast to previous optimal control approaches, which consider an average single nucleus, this closed-loop optimization is macroscopic. A 28% improvement in signal and 15% faster polarization rate is observed. Additionally, a strategy called Autonomously-optimized Repeated Linear Sweep (ARISE) is introduced to efficiently tailor existing hyperpolarization sequences in the presence of experimental uncertainty to enhance their performance. ARISE is expected to be broadly applicable in many experimental settings., 15 pages, 9 figures

Nuclear spin hyperpolarization provides a promising route to overcome the challenges imposed by the limited sensitivity of nuclear magnetic resonance. Here we demonstrate that dissolution of spin-polarized pentacene-doped naphthalene crystals enables transfer of polarization to target molecules via intermolecular cross relaxation at room temperature and moderate magnetic fields (1.45$\,$T). This makes it possible to exploit the high spin polarization of optically polarized crystals while mitigating the challenges of its transfer to external nuclei, particularly of the large distances and prohibitively weak coupling between source and target nuclei across solid-solid or solid-liquid interfaces. With this method, here we inject the highly polarized mixture into a benchtop NMR spectrometer and observe the polarization dynamics for target $^1$H nuclei. Although the spectra are radiation damped due to the high naphthalene magnetization, we describe a procedure to process the data in order to obtain more conventional NMR spectra, and extract the target nuclei polarization. With the entire process occurring on a timescale of one minute, we observe NMR signals enhanced by factors between -200 and -1730 at 1.45$\,$T for a range of small molecules., 8 pages, 4 figures

We report a transportable neutron spin filter based on the strong spin dependence of neutron proton scattering . The necessary high proton polarization is created by dynamic nuclear polarization (DNP) that uses short-lived optically excited triplet states instead of stable radicals, which eliminates the main path of nuclear spin lattice relaxation . The polarization can be preserved for many days under moderate experimental conditions and allows to realize a transportable spin filter which is conveniently polarized in the laboratory and then operated on a neutron beam line with practically frozen polarization maintained with a minimum of equipment. Using triplet DNP bulk proton spins in a pentacene doped single crystal of naphthalene have been polarized to a record value of 80% at a field of 0.36 T using a simple helium flow cryostat for cooling. This highly polarized sample can be transported in the compact cryostat without loss of polarization to a neutron beam line where it serves as a spin filter for polarization analysis in a neutron scattering experiment. Relaxation times of T 1 ∼ 800 h are achieved at a field of 20 mT and the polarization can be reversed by adiabatic fast passage with an efficiency of above 99%.

The Dzyaloshinskii-Moriya interaction (DMI) is believed to be operative in low-symmetry crystal structures lacking space-inversion symmetry. However, already in 1963, Arrott pointed out that even in a high-symmetry lattice, where the DMI would normally vanish, this interaction is present in the vicinity of any lattice defect. Based on these considerations and recent theoretical work, first experimental studies of the impact of the DMI on the spin-polarized magnetic small-angle neutron scattering (SANS) of polycrystalline magnets exhibiting a large density of microstructural defects have been performed. They demonstrated that an asymmetry in the difference between the two polarized SANS cross sections is induced by the DMI in nanocrystalline terbium and holmium as well as in mechanically-deformed microcrystalline cobalt. Here, we present a more complicated case, the nanocrystalline magnetically-textured soft magnet Vitroperm (Fe73Si16B7Nb3Cu1), where the interface between the FeSi nanoparticles and the amorphous magnetic matrix serves as the defect. The SANS cross section exhibits the polarization-dependent asymmetric term originating from the DMI. The effect has a magnetic field dependence and is less pronounced at higher fields until it eventually vanishes at full saturation. The result supports the generic relevance of the DMI for the magnetic structure of defect-rich ferromagnets. Furthermore, it shows that polarized SANS is a particularly powerful tool for investigating defect-induced DMI, which is a consequence of the unique dependence of the SANS cross section on the chiral interactions.

Under typical conditions for dynamic nuclear polarization (DNP)—temperature about 1 K or below and magnetic field about 3 T or higher—the polarization agent causes nuclear dipolar order to relax up to four orders of magnitude faster than nuclear polarization. However, as far as we know, this ultra-fast dipolar relaxation has thus far not been explained in a satisfactory way. We report similar ultra-fast dipolar relaxation of proton spins in naphthalene due to the photo-excited triplet spin of pentacene and propose a three-step mechanism that explains such ultra-fast dipolar relaxation by ground state electron spins as well as by photo-excited triplet spins: nuclear spin diffusion transfers nuclear dipolar order—that is nuclear dipolar energy—spatially to near the electron spins. Flip-flop transitions between nuclear spins near the electron spins convert this dipolar energy into electron-nuclear interaction energy. Finally electron spin–lattice relaxation or decay of the triplet spin transfers the latter type of energy to the lattice. We will show that this mechanism quantitatively explains the observed dipolar relaxation rate. The proposed mechanism is expected to contribute to dipolar relaxation in any spin system containing more than one spin species. It tends to create a stationary state, in which all dipolar interactions are combined in a single energy reservoir described by a single spin temperature. As an example we suggest that the addition of a relaxation agent in samples used for DNP may significantly accelerate the relaxation of the dipolar energy of the polarization agent, and as a result could possibly reduce the contribution of thermal mixing (TM) to DNP.

The antisymmetric Dzyaloshinskii-Moriya interaction (DMI) plays a decisive role for the stabilization and control of chirality of skyrmion textures in various magnetic systems exhibiting a noncentrosymmetric crystal structure. A less studied aspect of the DMI is that this interaction is believed to be operative in the vicinity of lattice imperfections in crystalline magnetic materials, due to the local structural inversion symmetry breaking. If this scenario leads to an effect of sizable magnitude, it implies that the DMI introduces chirality into a very large class of magnetic materials---defect-rich systems such as polycrystalline magnets. Here, we show experimentally that the microstructural-defect-induced DMI gives rise to a polarization-dependent asymmetric term in the small-angle neutron scattering (SANS) cross section of polycrystalline ferromagnets with a centrosymmetric crystal structure. The results are supported by theoretical predictions using the continuum theory of micromagnetics. This effect, conjectured already by Arrott in 1963, is demonstrated for nanocrystalline terbium and holmium (with a large grain-boundary density), and for mechanically-deformed microcrystalline cobalt (with a large dislocation density). Analysis of the scattering asymmetry allows one to determine the defect-induced DMI constant, $D = 0.45 \pm 0.07 \, \mathrm{mJ/m^2}$ for Tb at $100 \, \mathrm{K}$. Our study proves the generic relevance of the DMI for the magnetic microstructure of defect-rich ferromagnets with vanishing intrinsic DMI. Polarized SANS is decisive for disclosing the signature of the defect-induced DMI, which is related to the unique dependence of the polarized SANS cross section on the chiral interactions. The findings open up the way to study defect-induced skyrmionic magnetization textures in disordered materials.

We report the results of a small-angle neutron scattering (SANS) study on the magnetic microstructure of a textured Nd–Fe–B-based sintered permanent magnet. By combining unpolarized and polarized SANS (SANSPOL), we demonstrate that a number of important conclusions regarding the microscopic spin structure can be made. Specifically, the applied-field dependence of the unpolarized neutron data is in agreement with the existence of long-range spin-misalignment fluctuations, i.e., deviations of the magnetization from the mean direction on a real-space length-scale up to the micron range. In addition, measurements with polarized neutrons provide evidence for the presence of coupled nanometer-scale fluctuations in the nuclear and longitudinal magnetic scattering-length density.

A novel neutron spin filter whose principle is based on the strong spin dependence of the neutron scattering on protons has been developed. The dimensions of this filter are small, and it works very efficiently and is stable even in inhomogeneous fields. The protons in the naphthalene spin filter crystal are polarized by a recently developed method of dynamic nuclear polarization using photoexcited triplet states. This technique allows the design of a very compact apparatus that can be placed at a close distance to the sample under investigation. The application of this filter as a polarization analyzer is demonstrated in a magnetic small-angle neutron scattering experiment with the measurement of the spin-dependent scattering signals of a CuFeNi alloy. This sample has a pronounced textured structure factor of ferromagnetic precipitates in a paramagnetic matrix. The performance of the spin filter as an analyzer is illustrated by the excellent agreement of the experimental data with simulations based on a model of homogeneously magnetized spherical particles which are ordered in a simple cubic paracrystalline lattice.

A Drabkin-type spin resonator was designed and successfully implemented at the multi-purpose beam line BOA at the spallation neutron source SINQ at the Paul Scherrer Institute. The device selectively acts on the magnetic moment of neutrons within an adjustable velocity band and hence can be utilized as a tunable neutron beam monochromator. Several neutron time-of-flight (TOF) spectra have been recorded employing various settings in order to characterize its performance. In a first test application the velocity dependent transmission of a beryllium filter was determined. In addition, we demonstrate that using an exponential current distribution in the spin resonator coil the side-maxima in the TOF spectra usually associated with a Drabkin setup can be strongly suppressed.

A possibility of new type experimental searches for new physics beyond the standard model is being introduced in the symmetry tests in neutron-induced compound states according to the successful operation of intense pulsed neutron sources. The basis of experiment design is discussed.

We present the status of development of a novel neutron spin filter based on the strong spin dependence of the neutron scattering on protons. Using photo-excited triplet states for the dynamic nuclear polarization (DNP) process, proton polarization values of 80% can now be achieved in pentacene doped single crystals of naphthalene at a field of 0.36 T in a simple helium flow cryostat. Careful sample preparation lead to extremely long polarization decay times under moderate conditions that allowed us to develop a transportable device. The filter is polarized in the lab under well controlled conditions and is then transferred to the neutron beam line where it can be operated during several days with almost constant polarization while requiring only a minimum of equipment. We describe briefly the main features of the spin filter and its use as a spin analyzer in a small-angle neutron scattering (SANS) experiment probing the magnetic structure of a nanocrystalline soft magnetic material. Furthermore the procedure for performing the background and spin leakage corrections of the neutron data is outlined in detail.

yperpolarized magnetic resonance via dissolution dynamic nuclear polarization necessitates the transfer of thehyperpolarized molecules from the polarizer to the imager prior to in vivo measurements. This process leads to unavoid-able losses in nuclear polarization, which are difficult to evaluate once the solution has been injected into an animal. Wepropose a method to measure the polarization of the hyperpolarized molecules inside the imager bore, 3 s following dis-solution, at the time of the injection, using a precise quantification of the infusate concentration. This in situ quantifica-tion allows for distinguishing between signal modulations related to variations in the nuclear polarization at the time ofthe injection and signal modulations related to physiological processes such as tissue perfusion. In addition, our methodincludes a radical scavenging process that leads to a minor reduction in sample concentration and takes place within acouple of seconds following the dissolution in order to minimize the losses due to the presence of paramagnetic polar-izing agent in the infusate. We showed that proton exchange between vitamin C, the scavenging molecule and the deu-terated solvent shortens the long carboxyl13C longitudinal relaxation time in [1-13C]acetate. This additional source ofdipolar relaxation can be avoided by using deuterated ascorbate. Overall, the method allows for a substantial gain inpolarization and also leads to an extension of the time window available for in vivo measurements.

A polarized neutron Laue diffraction experiment on a single crystal of neodymium-doped lanthanum magnesium nitrate hydrate containing polarized proton spins is reported. By using dynamic nuclear polarization to polarize the proton spins, it is demonstrated that the intensities of the Bragg peaks can be enhanced or diminished significantly, whilst the incoherent background, due to proton spin disorder, is reduced. It follows that the method offers unique possibilities to tune continuously the contrast of the Bragg reflections and thereby represents a new tool for increasing substantially the signal-to-noise ratio in neutron diffraction patterns of hydrogenous matter.

The proton spins in a large naphthalene single crystal have been very efficiently polarized using optically excited triplet states of fully deuterated pentacene (C22D14) guest molecules. In a field of 0.3 T a proton polarization of 0.50 has been achieved. As technique for dynamic nuclear polarization (DNP) the integrated solid effect (ISE) scheme was employed to transfer the large electron polarization of the triplet states directly to the proton spins on naphthalene. © 2012 Elsevier B.V. All rights reserved.

A novel neutron spin resonance technique is presented based on the well-known neutron spin echo method. In a first proof-of-principle measurement using a monochromatic neutron beam, it is demonstrated that relative velocity changes of down to a precision of $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ can be resolved, corresponding to an energy resolution of better than 3 neV. Currently, the sensitivity is only limited by counting statistics and not by systematic effects. An improvement by another two orders of magnitude can be achieved with a dedicated setup, allowing energy resolutions in the 10 peV regime. The new technique is ideally suited for investigations in the field of precision fundamental neutron physics, but will also be beneficial in scattering applications.

In a test of principle a neutron spin filter has been built, which is based on dynamic nuclear polarization (DNP) using photo-excited triplet states. This DNP method has advantages over classical concepts as the requirements for cryogenic equipment and magnets are much relaxed: the spin filter is operated in a field of 0.3 Tat a temperature of about 100 K and has performed reliably over periods of several weeks. The neutron beam was also used to analyze the polarization of the target employed as a spin filter. We obtained an independent measurement of the proton spin polarization of similar to 0.13 in good agreement with the value determined with NMR. Moreover, the neutron beam was used to measure the proton spin polarization as a function of position in the naphthalene sample. The polarization was found to be homogeneous, even at low laser power, in contradiction to existing models describing the photo-excitation process. (C) 2012 Elsevier B.V. All rights reserved.

The use of polarized protons as a broad-band neutron spin filter is an attractive alternative to the well-established neutron polarization techniques, namely polarized 3He gas and super mirrors, since the spin-dependent neutron proton scattering cross-section is large in a broad wavelength range. We have developed a novel neutron spin filter where we create the necessary large proton polarization in a solid with a recent method of dynamic nuclear polarization (DNP) that uses photo-excited triplet states. This requires only moderate experimental means and allows a compact design. In order to quantify the efficiency of the spin filter, we have measured the relevant spin-dependent and spin-independent terms of the neutron scattering cross-section of a naphthalene single crystal. The data allows to estimate the triplet spin filter performance over a broad wavelength range. With the recently achieved proton polarization of 80% the triplet filter compares well with a state of the art 3He filter.

A new type of ultra-cold neutron (UCN) source based on the spallation process is under construction at PSI. The essential elements are a pulsed proton beam with highest intensity ( I p ≥ 2 mA ) and a low duty cycle (1%), a lead spallation target, a large D 2 O moderator and a solid deuterium ( sD 2 ) converter system. Spallation neutrons are thermalized in the D 2 O , further cooled and partially downscattered into the ultra-cold neutron range in the sD 2 . The expected UCN density is higher than 1000 UCN / cm 3 in typical experiments, an increase of almost two orders of magnitude over the best source currently available (at ILL). The new UCN source is expected to come into operation in 2009.

We have investigated the properties of the ultracold neutron converter materials deuterium D 2 , oxygen O 2 and heavy methane CD 4 in the temperature range between 8 K and room temperature. The experimental program was performed at the FUNSPIN beamline of the Swiss Spallation Neutron Source (SINQ) at Paul Scherrer Institut (PSI). In this paper the measured cold neutron total cross-sections for D 2 , O 2 and CD 4 are presented.

A compact apparatus to perform polarised neutron radiography on macroscopic objects is presented. Its working principle, based on Ramsey's resonance technique, allows to observe interactions between neutron spins and magnetic fields. Despite its shortness of only 480 mm, the magnetic field homogeneity allows for large beam cross-sections of up to 20×20 mm 2 . The applied magnetic field at the sample position is variable and can be tuned from about 4 to almost 32 mT without violating the Ramsey resonance condition. The performance of the apparatus is demonstrated in systematic tests, which show a phase stability of 1 degree and a sensitivity of about 7.5×10 −8 Tm.

Lithium is widely used in psychotherapy. The (6)Li isotope has a long intrinsic longitudinal relaxation time T(1) on the order of minutes, making it an ideal candidate for hyperpolarization experiments. In the present study we demonstrated that lithium-6 can be readily hyperpolarized within 30 min, while retaining a long polarization decay time on the order of a minute. We used the intrinsically long relaxation time for the detection of 500 nM contrast agent in vitro. Hyperpolarized lithium-6 was administered to the rat and its signal retained a decay time on the order of 70 sec in vivo. Localization experiments imply that the lithium signal originated from within the brain and that it was detectable up to 5 min after administration. We conclude that the detection of submicromolar contrast agents using hyperpolarized NMR nuclei such as (6)Li may provide a novel avenue for molecular imaging.

New low-temperature inserts compatible with an existing hyperpolarizer were developed to dynamically polarize nuclei in large samples. The performance of the system was tested on 8 ml glassy frozen solutions containing 13C-labeled molecules and doped with nitroxyl free radicals. The obtained 13C low-temperature polarization was comparable to the one measured on 20 times smaller sample volume with only 3–4 times higher microwave power. By using a dissolution insert that fits to the new design, it was possible to obtain about 120 ml of room-temperature hyperpolarized solution. The polarization as well as the molecule concentration was comparable to the values obtained in standard size hyperpolarized samples. Such large samples are interesting for future studies on larger animals and possibly for potential clinical applications.

Until recently the main application of dynamic nuclear polarization techniques has been in nuclear and particle physics, where they are used to polarize nuclei in bulk matter to be employed as polarized solid targets for particle beams probing the spin dependence of nuclear interactions. These techniques have now become most promising for applications in biomedical magnetic resonance and the knowledge gained in forty years of target development becomes of immediate interest.

A Ramsey apparatus for cold, polarised neutrons is described, which enables us to measure neutron precession angles with an absolute accuracy of about 1 ∘ . This is necessary to perform a planned high-accuracy measurement of the incoherent neutron scattering length b i , d of the deuteron. The performance of the apparatus is demonstrated in systematic stability measurements as well as in two selected examples using samples containing polarised nuclear spins.

A transmission neutron polariser (Fe/Si supermirror) has been successfully implemented in the small angle neutron scattering instrument SANS-I at the SINQ neutron source. The polariser is needed for investigations of magnetic nanostructures as well as for spin contrast variation techniques relying on the spin-dependent neutron scattering length of polarised nuclei. The V-shaped polariser is installed in the first section of the collimator system of the SANS instrument and its performance is optimised for neutrons with a wavelength between 0.5 and 1.0 nm. For a precise polarisation analysis of a beam with selectable incident divergence, such as in SANS experiments, an opaque spin filter is ideal. We used a solid polarised proton target exploiting the strong spin-dependent neutron scattering cross-section of hydrogen and determined the neutron beam polarisation to a precision of δ p / p ∼ 0.5 % for different collimations in a broad wavelength band.

Polarization observables in nuclear reactions with stable beams have provided important information concerning structural properties of nuclei and reaction mechanisms and hold great promise in the context of exotic nuclei. We report on the development of a polarized target based on plastic foils of 20–200 μm thickness to be used with radioactive ion beams. The operation of such a target requires a moderately high magnetic field and very low temperatures. The plastic foil is placed inside a chamber attached to the mixing chamber of a 3He–4He dilution refrigerator. Cooling of the foil is achieved via a superfluid film of 4He that can be supplied through two capillaries. The chamber has two thin, highly uniform silicon nitride windows. An NMR coil is attached to the target to monitor the polarization. Results of a first test to characterize the target system, using the elastic scattering of 38 MeV 12C by protons in inverse kinematics are presented.

Low-resolution small-angle neutron scattering measurements can benefit from polarized protons to generate scattering contrast profiles. In a recently developed technique, time-resolved polarized SANS tries to make use of spatial polarization gradients created around paramagnetic centres at the onset of dynamic nuclear polarization. The time constants which describe the build-up of polarization around the paramagnetic centre and the subsequent diffusion of polarization in the solvent were determined by analysing the temporal evolution of the nuclear polarization. The possible use and the limitations of this technique as a spectroscopic tool are discussed.

International audience; The efficiency of dissolution dynamic nuclear polarization can be boosted by Hartmann-Hahn cross polarization at temperatures near 1.2 K. This enables high throughput of hyperpolarized solutions with substantial gains in buildup times and polarization levels. During dissolution and transport, the C-13 nuclear spin polarization P(C-13) merely decreases from 45 to 40%.

Spin polarized probes are used in a wide range of experiments in nuclear physics including the determination of spin structure functions and tests of fundamental symmetries. At low energies, light stable polarized beams have been used for spectroscopic purposes. We propose to extend these types of experiments to nuclei far from stability by using radioactive ion beams (RIBs) and polarized targets. Towards this goal we intend to develop a solid polarized proton and/or deuterium target in the thickness range between 20 μm and 100 μm based on a scintillating (active) polymeric foil. Such a target would be a useful tool in the determination of excitation functions in resonant reactions, in studies of one-nucleon transfer reactions using RIBs as well as in probing the matter density of atomic nuclei. If scintillating, it could also help remove the background associated with the scattering of the radioactive beam.

Solid deuterium (sD2) will be used for the production of ultra-cold neutrons (UCN) in a new generation of UCN sources. Scattering cross sections of UCN in sD2 determine the source yield but until now have not been investigated. We report first results from transmission and scattering experiments with cold, very cold and ultra-cold neutrons on sD2 along with light transmission and Raman scattering studies showing the influence of the sD2 crystal properties.

Solid deuterium (sD 2 ) is a favourite converter material for the production of ultra-cold neutrons (UCN) in the next generation of UCN sources. In order to investigate sD 2 properties relevant for this purpose, an apparatus for the preparation and characterization of ortho-D 2 crystals has been built. It will be used for measurements of neutron transmission and scattering cross-sections as well as irradiation experiments with simultaneous optical control of the target conditions. The present paper describes the main components of the apparatus, i.e. the cryogenic optical D 2 cell, the gas system, the optical photography system and the Raman spectroscopy system.

For a proposed high-accuracy measurement of the spin-dependent neutron scattering length of the deuteron, a precise relative knowledge of the polarization of the proton and deuteron spin systems in the target material is needed. A simulation of the Q-meter system has been performed to get a quantitative estimate of the influence of various causes on the determination of the signal integral. Experimental and theoretical line shapes have been used as input to the model circuit. The response, i.e. the signal output, has been treated in a realistic way (e.g. integral determination, residual baseline fitting) and the effect of circuit parameter drifts has been analyzed. Several Q-meter system setups and measurement modes have been investigated with respect to inherent limitations and sensitivity to parameter drifts.

The understanding of few-nucleon systems at low energies is essential, e.g. for accurate predictions of element abundances in big-bang and stellar fusion. Novel effective field theories, taking only nucleons, or nucleons and pions as explicit degrees of freedom, provide a systematic approach, permitting an estimate of theoretical uncertainties. Basic constants parameterising the short range physics are derived from only a handful of experimental values. The doublet neutron scattering length a_2 of the deuteron is particularly sensitive to a three-nucleon contact interaction, but experimentally known with only 6% accuracy. It can be deduced from the two experimentally accessible parameters of the nd scattering length. We plan to measure the poorly known "incoherent" nd scattering length a_{i,d} with 10^{-3} accuracy, using a Ramsey apparatus for pseudomagnetic precession with a cold polarised neutron beam at PSI. A polarised target containing both deuterons and protons will permit a measurement relative to the incoherent np scattering length, which is know experimentally with an accuracy of 2.4\times 10^{-4}., 5 pages LaTeX2e, 1 .eps figure. To be published in Nucl. Inst. Methods A as part of the Proceedings of the 9th International Workshop on Polarized Solid Targets and Techniques in Bad Honnef (Germany), 27th - 29th October 2003

Analyzing powers of pion-proton elastic scattering have been measured at PSI with the Low Energy Pion Spectrometer LEPS as well as a novel polarized scintillator target. Angular distributions between 40 and 120 deg (c.m.) were taken at 45.2, 51.2, 57.2, 68.5, 77.2, and 87.2 MeV incoming pion kinetic energy for pi+ p scattering, and at 67.3 and 87.2 MeV for pi- p scattering. These new measurements constitute a substantial extension of the polarization data base at low energies. Predictions from phase shift analyses are compared with the experimental results, and deviations are observed at low energies., 15 pages, 4 figures

Polarized scintillating targets are now routinely available: protons, deuterons or other nuclei in blocks of scintillating organic polymer, doped with the free radical TEMPO, have been polarized dynamically in a field of 2.5 T in a vertical 3He−4He dilution refrigerator. A 19 mm diameter plastic lightguide carries the scintillation light from the sample in the mixing chamber to a photomultiplier outside the cryostat.

We report on a novel application of the Neutron Spin Phase Imaging technique, by performing polarised neutron radiography on dia- and paramagnetic samples. In order to achieve the necessary sensitivity we employed a 2.5 T Ramsey apparatus which was used in a previous experiment to measure the spin-dependent neutron scattering length of the deuteron. First successful results on aluminium, lead, titanium and heavy water (D 2 O) samples are presented. They are in good quantitative agreement with expected values deduced from susceptibility measurements.

The hydrogen nuclei in an organic scintillator have been polarized to more than 80% and the deuterons in its fully deuterated version to 24%. The scintillator, doped with TEMPO, has been polarized dynamically in a field of 2.5 T in a vertical dilution refrigerator in which a plastic lightguide transports the scintillation light from the sample in the mixing chamber to a photomultiplier outside the cryostat. Sizeable solid samples with acceptable optical properties and light output have been prepared and successfully operated as “live” polarized targets in nuclear physics experiments.

The study of the radiative neutron capture by protons, n+p→d+γ, provides valuable information about the nucleon–nucleon interaction. So far, no experimental value has existed for the γ-anisotropy which may appear if neutrons and protons both are polarised. A non-vanishing γ-anisotropy η is a clear-cut signal for the existence of transitions 3S1→3d1 from the triplet initial state to the ground state of the deuteron. We report the first measurement of this observable. The result is η=(1.0±2.5)×10−4 at 50.5% polarisation of neutrons and protons.

Dynamic nuclear polarization (DNP) has been performed in a magnetic field of 2.35 T at a temperature below 0.3 K in crystals of Nd 3+ : LaAlO 3 . A Q-meter NMR-system was used to measure the polarization of the 27Al and 139La nuclei and allowed to characterize the quality of the crystals. The 139La polarizations of +47.5% and −56.5% achieved represent an important step in the development of a polarized 139La target for a test of time reversal invariance in low-energy neutron reactions.

The precise knowledge of the neutron polarisation is needed in tests of the electroweak Standard Model using angular correlations in polarised neutron beta decay. We performed an experimental comparison study of two different methods of polarisation analysis of a cold neutron beam which are based on spin-dependent reflection, respectively, transmission. The compared devices are a supermirror analyser used in prior neutron decay studies and an opaque transmission spin filter of either polarised 3 He or polarised protons. The results of the neutron polarisation measured with the supermirror analyser and with the spin filter coincided in three different experiments within 0.1–0.2%.

Further progress in testing the structure of the electroweak interaction and in the precise determination of the weak coupling constants gA and gV by studying the decay of free polarized neutrons is presently limited by the accuracy to which the polarization of cold neutron beams can be measured. Current techniques of polarization analysis are based on neutron optical mirror reflection, and are systematically restricted to a precision of ≥0.25%. In this letter we introduce a new technique whereby systematic effects are strongly suppressed. The basic idea is to use an opaque spin filter, i.e., with analysing efficiency close to 100%, in analogy to an efficient polarizing foil in light optics. The method was successfully tested at the Institut Laue-Langevin in Grenoble in a comparison study, in which a well-defined neutron beam was analysed with two very different kinds of spin filters: a solid-state polarized proton target, using spin-dependent neutron scattering, and a spin filter of polarized 3 He gas, where spin-dependent neutron absorption is exploited. A difference in the neutron polarization of only 0.026(55)% was obtained, which demonstrates the power of the method.