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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%.

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.

We report on the development of a versatile cryogen-free laboratory cryostat based upon a commercial pulse tube cryocooler. It provides enough cooling power for continuous recondensation of circulating 4 He gas at a condensation pressure of approximately 250 mbar. Moreover, the cryostat allows for exchange of different cryostat-inserts as well as fast and easy “wet” top-loading of samples directly into the 1 K pot with a turn-over time of less than 75 min. Starting from room temperature and using a 4 He cryostat-insert, a base temperature of 1.0 K is reached within approximately seven hours and a cooling power of 250 mW is established at 1.24 K.

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.

In standard Dynamic Nuclear Polarization (DNP) electron spins are polarized at low temperatures in a strong magnetic field and this polarization is transferred to the nuclear spins by means of a microwave field. To obtain high nuclear polarizations cryogenic equipment reaching temperatures of 1 K or below and superconducting magnets delivering several Tesla are required. This equipment strongly limits applications in nuclear and particle physics where beams of particles interact with the polarized nuclei, as well as in neutron scattering science. The problem can be solved using short-lived optically excited triplet states delivering the electron spin. The spin is polarized in the optical excitation process and both the cryogenic equipment and magnet can be simplified significantly. A versatile apparatus is described that allows to perform pulsed dynamic nuclear polarization experiments at X-band using short-lived optically excited triplet sates. The efficient He-4 flow cryostat that cools the sample to temperatures between 4 K and 300 K has an optical access with a coupling stage for a fiber transporting the light from a dedicated laser system. It is further designed to be operated on a neutron beam. A combined pulse ESR/DNP spectrometer has been developed to observe and characterize the triplet states and to perform pulse DNP experiments. The ESR probe is based on a dielectric ring resonator of 7 mm inner diameter that can accommodate cubic samples of 5 mm length needed for neutron experiments. NMR measurements can be performed during DNP with a coil integrated in the cavity. With the presented apparatus a proton polarization of 0.5 has been achieved at 0.3 T. (C) 2013 Elsevier Inc. All rights reserved.

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.

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.

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.

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.

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.

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

The low-temperature magnetic properties of the rare-earth intermetallic compound system R3Pd20Si6(R = rare earth) were studied by elastic and inelastic neutron scattering. The compounds show due to the two rare-earth sublattices built from the 4a and 8c sites in the cubic crystal structure (space group Fm-3m) successive magnetic ordering with two different propagation vectors. In this report, we give an overview of the results obtained for the magnetic structures and the crystalline electric fields in the 3-20-6-system.

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 use of polarized protons as neutron spin filter is an attractive alternative to the well established neutron polarization techniques. The spin-dependent neutron scattering cross section of protons is usefully large up to the sub-Mev region. Employing optically excited triplet states for the dynamic nuclear polarization (DNP) of the protons, low temperatures and strong magnetic fields are not required and the apparatus can be simplified. The triplet DNP method can be used to build a reliably working neutron spin filter that is operated in 0.3T and about 100 K. The high proton polarization of 0.5 obtained is presently still limited by the cooling of the sample. The corresponding analyzing power of A ~ 0.5, obtained with the 5 mm thick sample, can be further increased using a longer sample. Interesting possibilities for a triplet spin filter are opened by the use of neutron optics elements that allow to adapt the beam to the filter cross section.

At the temperatures T N1 ≈2.4 K and T N2 ≈0.7 K, the cubic intermetallic compound Nd 3 Pd 20 Si 6 undergoes second order magnetic phase transitions. Here we report on the magnetic structures obtained from low-temperature neutron diffraction data by using a He dilution refrigerator, and on the crystalline electric field splitting of the Nd 3+ ground state multiplet 4 I 9/2 obtained from inelastic neutron scattering data.

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.

We are developing small arrays of microcalorimeters based on transition edge sensors made with Mo/Au bilayers deposited on silicon nitride membranes and Au absorbers. The superconducting transition of the bilayers is adjusted to be around 130 mK with a transition width better than a millikelvin by use of the proximity e!ect between the Au and Mo "lms. We built a dilution refrigerator and wired it for 2 channel operation in order to study thermal coupling issues between thermometers within the array. The device fabrication procedure as well as preliminary results are presented. ( 2000 Elsevier Science B.V. All rights reserved.

The new nucleon area (NA) at PSI is designed as a multi-purpose facility with nucleon beams. The area can be used for experiments with polarized or unpolarized protons or neutrons. For both kinds of nucleons the available energy ranges from about 100 MeV up to a maximum of about 590 MeV.

Polarization transfer measurements in π+ elastic scattering have been performed at two incident pion energies, one below and one at the Δ(3, 3)-resonance. Using a vector polarized deuteron target four polarization transfer observables are determined. The results are compared to predictions from Faddeev calculations.

An intensive program of n-p measurement of spin observables in elastic and pion production reactions has been performed at the Paul Scherrer Institute taking advantage of the high intensity polarized neutron beam. In the elastic reaction 16 different spin observables have been measured for kinetic energies from 210 to 590 MeV with the centre of mass angular range from 60 to 180 degrees. This will allow to perform direct reconstruction in the model independent way of the isospin I=0 scattering amplitudes in elastic NN interaction. Three body final state process \(\vec np - pp\pi ^ - \) with polarized neutrons in exclusive experiment has been investigated.

A new neutron imaging technique is proposed, which is based on the position sensitive measurement of the phase shift of neutron spin precession. This phase shift, caused either by magnetic or pseudomagnetic fields produced by the investigated object, is measured using a Ramsey-setup for polarised, cold neutrons combined with a ccd-camera commonly used for neutron radiography. The feasibility of the method has been demonstrated in preliminary tests performed at the cold neutron beamline FUNSPIN at Paul Scherrer Institute.

The kinetic energy spectrum and the polarization of the PSI neutron beam produced in the reaction 12C(p,n)X at 0° with 590 MeV polarized protons were investigated. A strong energy dependence of the neutron beam polarization is observed which was not expected at the time the neutron beam was built.

The analyzing power, $A_{oono}$ , and the polarization transfer observables $K_{onno}$ , $K_{os''so}$ and $K_{os''ko}$ have been measured in neutron-proton elastic scattering at 260, 318, 386, 472 and 538 MeV for c.m. scattering angles between 64° and 160°. The data were obtained at PSI with a polarized neutron beam and a polarimeter analyzing the transverse polarization of the outgoing proton. They make a significant impact on the knowledge of the Isospin I = 0 nucleon-nucleon scattering.

Polarization transfer observables in π + d elastic scattering have been measured for the first time. Four polarization transfer parameters were determined at pion energies T π =134 MeV and 180 MeV at scattering angles θ π ,C.M. between 100° and 140° using a deuteron target polarized perpendicular to the scattering plane and a deuteron tensor polarimeter. The data are compared to different predictions from the SAID phase shift analysis and Faddeev calculations.

Polarization transfer measurements in π+ elastic scattering have been performed at two incident pion energies, one below and one at the Δ(3, 3)-resonance. Using a vector polarized deuteron target four polarization transfer observables are determined. The results are compared to predictions from Faddeev calculations.

Polarized neutron scattering from dynamically polarized targets has been used for the study of hydrogenous materials in several laboratories. A new variant, which is less dependent on specific deuteration, is proposed. This is based on the observation that a radio frequency (RF) field swept over a selected part of an NMR line depolarizes the spins depending on their spatial distribution in and around paramagnetic molecules. An RF field swept over a narrow frequency interval has little effect on polarized nuclear spins in the paramagnetic centers, whereas remote nuclear spins can be depolarized. When applying the sweep over a much larger frequency range, all spins are depolarized. This was observed both by NMR and by polarized neutron scattering after selective depolarization of the proton spins in a solid solution of protonated EHBA–CrV, Na(C12H20O7CrV).D2O, in a mixture of deuterated glycerol and water. The decay time of proton spin polarization in domains associated with the paramagnetic centers varies between 5 h in a deuterated solvent and less than 1 min in a protonated solvent. The size of such a domain is barely larger than 1 nm. The same observation is also made when the nuclear polarization is reversed by adiabatic fast passage. If the RF sweep is limited to frequencies close to the central peak of the proton NMR line, the proton spins far away from the paramagnetic centers are reversed, whereas those of EHBA–CrV and close to the centers maintain their original polarization. This method may become a useful tool in neutron scattering once the paramagnetic centers can be fixed as spin labels to well defined sites in a macromolecule, preferably in a crystal lattice.

In this article we report the results of an experiment performed in 1993 at PSI. The goal was to determine the absolute rate of nuclear muon capture by3He. In the experiment we used a new technique recently developed at Gatchina. As a preliminary result from this experiment we obtainedλ c=(1496±3(stat)-3(syst)) s−1.

The triton energy spectrum of the muon capture reaction mu(3)He --> t + v(mu), where mu(3)He is the ground state of muonic He-3, has been measured by means of a high-pressure ionization chamber in order to investigate a possible heavy v admixture into the mu flavor with high sensitivity. The upper limit of the mu-heavy v(i) mixing matrix element squared was obtained to be U-mu i((2) less than or equal to 10(-3) for heavy neutrino masses in the range 25 less than or equal to E(ov) less than or equal to 75 MeV.

The results of measurements performed to assess the potential of deuterated TEMPO and deuterated oxo-TEMPO for DNP are presented. These free radicals became available only recently. Polarization and relaxation processes of protons and deuterons in various deuterated alcohols and deuterated polymers have been investigated. More than 40% deuteron polarization has been obtained in samples of fully deuterated polystyrene.

This work is part of an ongoing project to develop a Superheated Superconducting Granule (SSG) detector for cold dark matter and neutrinos. The response of SSG devices to nuclear recoils has been explored irradiating SSG detectors with a 70MeV neutron beam. The aim of the experiment was to test the sensitivity of Sn, Al and Zn SSG detectors to nuclear recoil energies down to a few keV. The detector consisted of a hollow teflon cylinder (0.1cm$^3$ inner volume) filled with tiny superconducting metastable granules embedded in a dielectric medium. The nuclear recoil energies deposited in the SSG were determined measuring the neutron scattering angles with a neutron hodoscope. Coincidences in time between the SSG and the hodoscope signals have been clearly established. In this paper the results of the neutron irradiation experiments at different SSG intrinsic thresholds are discussed and compared to Monte Carlo simulations. The results show that SSG are sensitive to recoil energies down to $\sim$1keV. The limited angular resolution of the neutron hodoscope prevented us from measuring the SSG sensitivity to even lower recoil energies., 14 pages in pure LaTeX, 17 figures available on request from schmiemann@lhep.unibe.ch, submitted to Phys. Rev. D, August 1994

The vector analyzing power [ital iT][sub 11] and the tensor analyzing power [tau][sub 22]=[ital T][sub 22]+[ital T][sub 20]/ [radical]6 have been measured for [pi][sup +][r arrow][sup 6]L[rvec i] elastic and inelastic scattering (to the 3[sup +]0, 2.19 MeV state) at incident pion energies of 120, 150, 180, and 194 MeV. These data and earlier ones from our group are compared with new coupled channels calculations. Within the coupled channels model, the influence of different nuclear wave functions, the strength of the coupling of the ground and first excited states, and the effects of the phenomenological second-order potential were investigated. It was found that the calculated vector analyzing power [ital iT][sub 11] depends strongly on the transverse form factor whichever nuclear wave function is chosen. In the angular region where the [ital iT][sub 11] data were taken the coupling of the ground to the first excited state has a minor effect on the theoretical predictions. Reasonable agreement with the data can be obtained for a large energy and angular region with the first-order potential only.

The inclusive vector analyzing power [ital iT][sub 11] of [pi][sup +][r arrow][sup 7]Li elastic scattering and inelastic scattering to the 0.47 MeV excited state was measured at several angles for [ital T][sub [pi]]=134, 164, and 194 MeV. The polarization effects were found to be small but nonzero, the trend of the data is well described by a coupled channels calculation. The results of the calculation are more sensitive to variations of the nuclear structure input than to variations of the reaction mechanism.

The ordering of the Ce3+ magnetic moments in the heavy-fermion compound CePdAl was investigated by means of neutron powder diffraction measurements of high-quality polycrystalline samples at temperatures down to 180 mK. The triangular coordination symmetry of the magnetic ions gives rise to geometrical frustration and leads to an incommensurate antiferromagnetic structure, exhibiting a coexistence of ordered and frustrated disordered Ce moments. The magnetic propagation vector shows a pronounced temperature dependence below TN and locks in to k= \(\frac\Box1\Box\Box2\Box\),0,τ , τ=0.351, below 1.9 K. The magnetic structure at 180 mK could unambiguously be determined and the coexistence of ordered and disordered Ce moments is observed even at the lowest temperatures. A second magnetic phase transition can be excluded.

The ORPHEUS dark matter experiment is completed at our shallow depth laboratory in Bern (70 m.w.e.). The detector relies on measuring the magnetic flux variation produced by weakly interacting massive particles (WIMPs) as they heat 30 μm diameter superheated superconducting tin granules (SSG) and induce superconducting-to-normal phase transitions. In an initial phase, 0.45 kg of tin granules in a segmented detector volume have been used. Preliminary results of the experiment will be reported.