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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%.

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.

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.

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.

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 (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

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.

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.

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.

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.

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 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.

We present results of an irradiation of a Superheated Superconducting Granule (SSG) detector with a 70 MeV neutron beam. The aim of the experiment was to measure the sensitivity of the detector to nuclear recoil energies produced by elastically scattered neutrons. The detector consists of a small readout coil (diameter 5 mm, length 10 mm) filled with aluminum granules of average diameter 23 μm embedded in an Al2O3 granulate with a 6% volume filling factor. The neutron scattering angles were determined using a scintillator hodoscope. Coincidences in time between the SSG and the hodoscope signals have been clearly established. Data were taken at an operating temperature of 120 mK for different SSG intrinsic thresholds. The results prove the sensitivity of the detector to nuclear recoils in the energy range of a few keV. The data show good agreement with the global heating mechanism.

We have measured the spin-dependent total cross-section difference Δσ L in neutron-proton scattering at 66 MeV which is highly sensitive to the 3 S 1 - 3 D 1 mixing parameter e 1 . The result Δσ L = −(26.5 ± 1.2 ± 1.6) mb is in good agreement with recent phase-shift analyses that require a large e 1 (a stronger tensor force).

A polarized neutron beam at PSI has been used to measure the spin-dependent neutron-proton total cross sections Δσ L and Δσ T from 140 to 590 MeV. The results are compared with recent phase-shift calculations.

The design and characteristics of a compact versatile 3 He evaporation/ 3 He 4 He dilution refrigerator with central access to the mixing chamber are described. The sample holding device and /or the refrigerator unit can be removed from or inserted into the cryostat at 4 K. The apparatus is reliable and service-friendly. The version with a continuous heat exchanger reaches 50 mK, and at 100 mK its cooling power is 1 mW. A version with two sintered silver heat exchangers reaches around 30 mK.

At PSI a polarized neutron beam facility has been set up and was used to measure neutron-proton total cross section differences ΔσL and ΔσT in the energy range from 140 to 590 MeV.

A progress report of the ORPHEUS dark matter experiment in the Bern Underground Laboratory is presented. A description of the ORPHEUS detector and its sensitivity to WIMPs is given. The detector will consist of 1 to 2 kg Sn granules operating in a magnetic field of approximately 320 G and at a temperature of 50 mK. In the first phase, the detector will be read out by conventional pickup coils, followed by a second phase with SQUID loops. Preliminary results on background and radioactivity measurements are shown.

A SSG detector has been tested in a first long-lasting experiment. It consisted of 13 g of tin granules with diameters of 29±0.5 μm embedded in Teflon powder with a volume filling factor of 11%. The detector has been exposed to cosmic rays and radioactive sources and has been kept for seven weeks at a constant temperature of 70 mK followed by shorter periods at 545 mK and 1.04 K. The detector performance as well as results of rate measurements are presented. These tests were made in preparation of the ORPHEUS dark matter experiment.

Spin-polarization reversal by the use of the adiabatic fast passage mechanism has been investigated in a variety of polarized target materials. The high efficiencies achieved open the way to the application of the AFP method in operational polarized solid targets.

First results of DNP at 2.5 T and below 0.3 K in thin polymer foils and tubes with the chemical composition (CX2)n, [ X = 1 H, 2 D, 19 F ], doped with TEMPO, are presented. Appreciable polarization of protons, deuterons, and 19F-nuclei were obtained. The samples can be handled at room temperature for several hours, and therefore they are suitable for new applications.

For measurements of the 2-spin and 3-spin transfer parameters in the n-p system in the 300–600 MeV range, a large (100 cm 3 ) frozen spin polarized target has been built and put into operation at PSI. The holding coil system allows a virtually arbitrary polarization direction, quick polarization reversal and large opening angles.

Elastic and inelastic neutron scattering has been employed to study the quadrupolar and dipolar ordering phenomena in DyPd 3 S 4 . At T Q =3.4 K the Dy quadrupole moments undergo a phase transition to an ordered lattice, reflected by a distinct change of the crystal-field level scheme observed by neutron spectroscopy. At T N1 ≈1 K a phase transition of the Dy dipole moments to a long-range canted antiferromagnetic state is observed, followed by a second magnetic phase transition at T N2 ≈0.75 K characterized by a change of the canting angle.

Polarized neutron scattering from dynamic polarized targets is a new tool of macromolecular structure research. In frozen nuclear spin targets the polarization of isotopes can be eliminated selectively one by one till only a single isotope is left polarized. This technique has been applied successfully in biological structure research. It is extended to discriminate between nuclear spins of the same isotope.

First results of DNP at 2.5 T and below 0.3 K in F-dimethylcyclohexane (C 8 F 16 ), doped with F-2,4-dimethyl-3-ethyl-3-pentyl (C 9 F 19 ), are presented. A polarization of the 19 F-nuclei of up to 54% was obtained.

The resistance of some Si:P samples has been measured as a function of the temperature in the range 0.4–1 K in view of their possible use as cryogenic calorimeters. The comparison with the theoretical predictions have been extended to the range 0.4–5.0 K using the results of previous unpublished measurements.

Full angular distributions of the differential cross-section dσ/dμ and of the analysing power Ay in p p elastic scattering have been measured at 697 MeV/c. The results of Ay are compared with the predictions of various theoretical models.

This paper deals with a special Pomeranchuk cooling device which is used in combination with a He 4 -cycling He 3 -He 4 dilution refrigerator at high pressures. The lowest temperature obtained was 1.1 mK.

Droplets of diluted 3He are observed to fall from the upper inlet superleak of a glass, 4He-cycling dilution refrigerator [1]. Their diameter and velocity are measured. Droplets of concentrated 3He are observed to ascend from the lower outlet superleak to the phase separation surface.

Measurements are presented of liquid-solid phase transitions in 3He-4He mixtures contained in a cell with flexible walls. From adiabatic compressibility measurements between 50 mK and 300 mK we determined the pressures at which a three-phase equilibrium exists between almost pure solid 4He (hcp), diluted liquid 3He (L1) and almost pure liquid 3He (L2). At T = 0 the L1 phase appeared to exist up to a pressure of 2.577 MPa, well above the melting pressure of 4He (2.53 MPa). At higher pressures we found that a decrease of the volume of a hcp-L2 mixture results in selfcooling, apparently due to conversion of L2 into solid bcc2 mixture along the hcp-bcc2-L2 univariant. This compressional cooling effect was observed in the temperature range from 340 mK to 24 mK at pressures between 2.8 MPa and 3.4 MPa.

Differential susceptibility measurements were performed on a single crystal of RbCoCl3 · 2H2O. An anti-ferromagnetic ordering was found at 2.975 K.