Maier-Leibnitz Zentrum Research Articles

Instrument developments and recent scientific highlights at the J-NSE

The J-NSE neutron spin echo spectrometer faces now 10 years of successful user operation at the FRM II research reactor at the Heinz Maier-Leibnitz Zentrum (MLZ). We present scientific highlights and instrumental developments of the last decade, for example the development of grazing incidence neutron spin echo spectroscopy (GINSES) at the J-NSE and investigations of the dynamics at solid-liquid interfaces with this new option. Polymers in confinement have been a prominent topic, as well as the internal dynamics of proteins. The scientific questions also triggered instrumental developments such as a new polarizer and a new neutron guide concept. Finally, the future of the J-NSE will be addressed with a short presentation of the current upgrade program with superconducting main coils with reduced intrinsic field integral inhomogeneity.

The Thermal Neutron Beam Option for NECTAR at MLZ

The beam port SR10 at the neutron source FRM II of Heinz Maier-Leibnitz Zentrum (MLZ) is equipped with a moveable assembly of two uranium plates, which can be placed in front of the entrance window of the beam tube via remote control. With these plates placed in their operating position the thermal neutron spectrum produced by the neutron source FRM II is converted to fission neutrons with 1.9 MeV of mean energy. This fission neutron spectrum is routinely used for medical applications at the irradiation facility MEDAPP, for neutron radiography and tomography experiments at the facility NECTAR and for materials testing. If, however, the uranium plates are in their stand-by position far off the tip of the beam tube and the so-called permanent filter for thermal neutrons is removed, thermal neutrons originating from the moderator tank enter the beam tube and a thermal spectrum becomes available for irradiation or activation of samples. By installing a temporary flight tube the beam may be used for thermal neutron radiography and tomography experiments at NECTAR. The thermal neutron beam option not only adds a pure thermal neutron spectrum to the energy ranges available for neutron imaging at MLZ instruments but it also is an unique possibility to combine two quite different neutron energy ranges at a single instrument including their respective advantages.The thermal neutron beam option for NECTAR is funded by BMBF in frame of research project 05K16VK3.

Implementation of a new Cryopad on the diffractometer POLI at MLZ.

A new polarized neutron single crystal diffractometer POLI (Polarization Investigator) has been developed at the Maier-Leibnitz Zentrum, Garching, Germany. After reviewing existing devices, spherical neutron polarimetry has been implemented on POLI as a main experimental technique using a third-generation cryogenic polarization analysis device (Cryopad) built in cooperation between RWTH University and Institut Laue-Langevin. In this report we describe the realization and present the performance of the new Cryopad on POLI. Some improvements in the construction as well as details regarding calibrations of Cryopad and its practical use are discussed. The reliable operation of the new Cryopad on POLI is also demonstrated.

Evaluation of the dark signal performance of different SiPM-technologies under irradiation with cold neutrons

In this paper we report the results of the assessment of changes in the dark signal delivered by three silicon photomultiplier (SiPM) detector arrays, fabricated by three different manufacturers, when irradiated with cold neutrons (wavelength λn=5Å or neutron energy of En=3.27meV) up to a neutron dose of 6×1012n/cm2. The dark signals as well as the breakdown voltages (Vbr) of the SiPM detectors were monitored during the irradiation. The system was characterized at room temperature. The analog SiPM detectors, with and without a 1mm thick Cerium doped 6Li-glass scintillator material located in front of them, were operated using a bias voltage recommended by the respective manufacturer for a proper detector performance. Iout-Vbias measurements, used to determine the breakdown voltage of the devices, were repeated every 30s during the first hour and every 300s during the rest of the irradiation time. The digital SiPM detectors were held at the advised bias voltage between the respective breakdown voltage and dark count mappings repeated every 4min. The measurements were performed on the KWS-1 instrument of the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching, Germany. The two analog and one digital SiPM detector modules under investigation were respectively fabricated by SensL (Ireland), Hamamatsu Photonics (Japan), and Philips Digital Photon Counting (Germany).

Characterization of the NEPOMUC primary and remoderated positron beams at different energies

We report on the characterization of the positron beam provided at the open beam port of the NEPOMUC facility at the Heinz Maier-Leibnitz Zentrum (MLZ) Garching. The absolute positron flux of the primary beam at 400eV and 1keV kinetic energy and of the remoderated beam at 5, 12 and 22eV were determined. Energy-dependent intensities in the range of (1–5)·108e+/s and (2–6)·107e+/s have been observed for the primary and remoderated beam, respectively. We attribute the significant losses for the primary beam, in comparison with the expected value, to the non-adiabatic positron guiding in the beam line. We also measured the longitudinal energy distribution of the remoderated beam, yielding an energy spread below 3.3eV. The mean transverse energy of the remoderated beam, determined from measurements in different final magnetic fields, was found to be below 1.3eV. These results are likely to apply to the NEPOMUC beam delivered to other user stations.

DNS: Diffuse scattering neutron time-of-flight spectrometer

DNS is a versatile diffuse scattering instrument with polarisation analysis operated by the Jülich Centre for Neutron Science (JCNS), Forschungszentrum Jülich GmbH, outstation at the Heinz Maier-Leibnitz Zentrum (MLZ). Compact design, a large double-focusing PG monochromator and a highly efficient supermirror-based polarizer provide a polarized neutron flux of about 107 n cm-2 s-1. DNS is used for the studies of highly frustrated spin systems, strongly correlated electrons, emergent functional materials and soft condensed matter.

J-NSE: Neutron spin echo spectrometer

Neutron Spin-Echo (NSE) spectroscopy is well known as the only neutron scattering technique that achieves energy resolution of several neV. By using the spin precession of polarized neutrons in magnetic field one can measure tiny velocity changes of the individual neutron during the scattering process. Contrary to other inelastic neutron scattering techniques, NSE measures the intermediate scattering function S(Q,t) in reciprocal space and time directly. The Neutron Spin-Echo spectrometer J-NSE, operated by JCNS, Forschungszentrum Jülich at the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching, covers a time range (2 ps to 200 ns) on length scales accessible by small angle scattering technique. Along with conventional NSE spectroscopy that allows bulk measurements in transmission mode, J-NSE offers a new possibility - gracing incidence spin echo spectroscopy (GINSENS), developed to be used as "push-button" option in order to resolve the depth dependent near surface dynamics.

Development and Test of a Neutron Imaging Setup at the PGAA Instrument at FRM II

We report on the developments of a neutron tomography setup at the instrument for prompt gamma-ray activation analysis (PGAA) at the Maier-Leibnitz Zentrum(MLZ). The recent developments are driven by the idea of combining the spatial information obtained with neutron tomography with the elemental information determined with PGAA, i.e. to further combine both techniques to an investigative technique called prompt gamma activation imaging (PGAI).At the PGAA instrument, a cold neutron flux of up to 6 x 1010 cm-2 s-1 (thermal equivalent) is available in the focus of an elliptically tapered neutron guide. In the reported experiments, the divergence of the neutron beam was investigated, the resolution of the installed detector system tested, and a proof-of-principle tomography experiment performed.In our study a formerly used camera box was upgraded with a better camera and an optical resolution of 8 line pairs/mm was achieved. The divergence of the neutron beam was measured by a systematic scan along the beam axis. Based on the acquired data, a neutron imaging setup with a L/D ratio of 200 was installed. The resolution of the setup was testedin combination with a gadolinium test target and different scintillator screens. The test target was irradiated at two positions to determine the maximum resolution and the resolution at the actual sample position. The performance of the installed tomography setup was demonstrated bya tomography experiment of an electric amplifier tube.

High-flux PGAA for milligram-weight samples

With the high-intensity cold neutron flux available at the Prompt Gamma Activation Analysis (PGAA) instrument of the research reactor FRM II at the Heinz Maier-Leibnitz Zentrum (MLZ), samples with a weight of 1 mg or even less can be investigated for their elemental compositions using the (n,γ) capture reaction. In such cases, the typical sample packing material for PGAA experiments made of 25 μm thick PTFE foil (ca. 80 mg) can be orders of magnitude more massive than the sample weight itself. Proper choice of the packing material and measuring conditions are then of the highest importance [1].

In Operando Small-Angle Neutron Scattering (SANS) on Li-Ion Batteries

Small-angle neutron scattering is a tool providing information on nanostructures of objects in the order of 1-300 nm. In this experiment a pouch bag lithium ion battery cell was investigated with SANS ex situ, in situ and in operando during charging and discharging. LiNi0.33Mn0.33Co0.33O2 was used as cathode and graphite as anode material. The small-angle neutron scattering measurements were performed on the SANS-1 instrument at the FRM II neutron source of the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching, Germany. Ex situ measurements of components of the cell as well as static in situ and dynamic in operando SANS experiments were performed with a complete Li-ion pouch bag cell. The cell was charged and discharged twice with C/3 and small-angle neutron scattering data were collected during the measurements. The observed intensity data were then evaluated and changes of the total scattering in the measured Q-range are correlated to the lithiation processes occurring inside the cell. Thus we can show that SANS can be used as a tool to monitor kinetic processes in Li-ion batteries in operando and non-destructively.

Neutron crystal structure of human FPPS complexed with risedronate

Nitrogen-containing bisphosphonates (N-BPs), such as risedronate and zoledronate, are currently used as clinical drug for bone-resorption diseases and are potent inhibitor of farnesyl pyrophosphate synthase (FPPS). The potential of N-BPs as antitumor agents has also been suggested by the several in vitro and in vivo preclinical studies. However, BP drugs limit their therapeutic use to bone-related diseases, because BPs are highly charged and water soluble molecules. X-ray crystallographic analyses of FPPS with N-BPs have revealed that N-BPs bind to FPPS with three magnesium ions and several water molecules. In order to develop a novel FPPS inhibitor, the hydrogen-bond networks formed by FPPS, BPs and water molecules are necessary to be elucidated. To understand the structural characteristics of N-BPs bound to FPPS, including hydrogen atoms and hydration by water, neutron diffraction studies were initiated using BIODIFF at the Heinz Maier-Leibnitz Zentrum (MLZ). FPPS-risedronate complex crystals of approximate dimensions 2.8 × 2.5 × 1.5 mm (~ 3.5 mm3) were obtained by repeated macro-seeding. Monochromatic neutron diffraction data were collected to 2.4 Å resolution with 98.4% overall completeness and 10.7% Rmerge. As a result of X-ray/neutron joint refinment, R and Rfree values for the neutron data were 19.6 and 23.3%, respectively. This neutron structure clearly reveals the protonation state of risedronate, hydration in the inhibitor-binding region. Furthermore, the amide H/D exchange analysis showed that there is a highly rigid region which regulate the structural change upon the binding of the ligands. Here we will discuss the detailed hydrogen-bond network and the protonation state of FPPS and risedronate.

Application of Small Angle Neutron Scattering for In Situ Measurements of Li-Ion Batteries

Small-angle scattering is a commonly used to gain informations about the nanostructure of the investigated materials (i.e. size, volume and shape of particles). Also, neutrons are a powerful tool for in-situ investigations because of their high material penetration depths. Therefore SANS is well suited for studying any changes of these parameters inside closed battery cells under operation. Up to now only a few publications exist dealing with the SANS method for batteries and battery materials. This is mainly caused by the fact that only new developed batteries provide a reasonable thickness for transmission measurements necessary for the applied method.In 2012 Bridges et al. used a Li||Graphite coin cell for an in-situ SANS experiment, observing the growth of the anodic SEI-layer [1], while for example Nagao et al. used the method to investigate the Li-intercalation mechanism in carbon host materials [2].However, one major drawback in these experiments is that only cells with Li-metal as counter electrode were used.In our approach we assemble experimental cells consisting of the same anode and cathode materials as used in commercial cells and perform in-situ SANS experiment during charging/discharging. The cells are assembled as pouch bag or coffee bag cells.We report on our measurements with the SANS-1 instrument at Heinz Maier-Leibnitz Zentrum (MLZ), Garching. In-situ small-angle neutron scattering data of NMC||Separator||Graphite cells was collected during a complete charging and discharging cycle. In addition single battery components were measured separately to distinguish the various component signals. The in-situ data shows a variation of the integrated total scattering intensity in dependence of the state of charge. The quite noticeable step in the curve can be associated with the volume changes of the cathode or anode materials caused by the Li-intercalation process. Combining the different data sets a feasible interpretation of the charging/discharging process will be presented.Our future aim is to further develop the in-situ small-angle neutron scattering technique to be able to monitor aging and electrode deterioration processes without the need to open the cells.[1] Bridges, C. A., X.-G. Sun, J. Zhao, M. P. Paranthaman and S. Dai. "In Situ Observation of Solid Electrolyte Interphase Formation in Ordered Mesoporous Hard Carbon by Small-Angle Neutron Scattering." The Journal of Physical Chemistry C, 2012, 116(14), 7701-7711.[2] Nagao, M., C. Pitteloud, T. Kamiyama, T. Otomo, K. Itoh, T. Fukunaga, K. Tatsumi and R. Kanno. "Structure Characterization and Lithiation Mechanism of Nongraphitized Carbon for Lithium Secondary Batteries." Journal of The Electrochemical Society, 2006, 153(5), A914-A919.

Investigations of early stage precipitation in a tungsten-rich nickel-base superalloy using SAXS and SANS

Characterization of the early stage precipitation is an important issue as it controls the emerging microstructure developed on Ni-based superalloys which are used as single crystal blades in gas turbines. The difficulty is that the gamma prime precipitation occurs at high temperatures and the reaction kinetic is very fast. Therefore, experimental methods with high time resolution are needed to monitor γ′ precipitation. By using the high flux synchrotron instrument HARWI-II set up of the Helmholtz–Zentrum Geesthacht with a fast data collection detector, it was possible to observe the creation of fine precipitates and their early growth in a tungsten-rich Ni-base superalloy. The cooling down of the superalloy from the single-phase region to lower temperatures already leads to the formation of precipitates in the size range of a few nm. The formation and growth of the precipitates at this early stage is described in detail. In addition, SANS measurements were performed at the new SANS-1 instrument at Maier–Leibnitz Zentrum (MLZ) in Garching to extend the results to larger precipitate sizes. DSC experiments were used to determine the critical temperatures of the formation of these fine precipitates, as well as the temperature at which they dissolve during heating (γ′ solvus temperature).

Crystallization and preliminary neutron diffraction experiment of human farnesyl pyrophosphate synthase complexed with risedronate

Nitrogen-containing bisphosphonates (N-BPs), such as risedronate and zoledronate, are currently used as a clinical drug for bone-resorption diseases and are potent inhibitors of farnesyl pyrophosphate synthase (FPPS). X-ray crystallographic analyses of FPPS with N-BPs have revealed that N-BPs bind to FPPS with three magnesium ions and several water molecules. To understand the structural characteristics of N-BPs bound to FPPS, including H atoms and hydration by water, neutron diffraction studies were initiated using BIODIFF at the Heinz Maier-Leibnitz Zentrum (MLZ). FPPS-risedronate complex crystals of approximate dimensions 2.8 × 2.5 × 1.5 mm (∼3.5 mm(3)) were obtained by repeated macro-seeding. Monochromatic neutron diffraction data were collected to 2.4 Å resolution with 98.4% overall completeness. Here, the first successful neutron data collection from FPPS in complex with N-BPs is reported.

Neutron diffraction studies towards deciphering the protonation state of catalytic residues in the bacterial KDN9P phosphatase.

The enzyme 2-keto-3-deoxy-9-O-phosphonononic acid phosphatase (KDN9P phosphatase) functions in the pathway for the production of 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid, a sialic acid that is important for the survival of commensal bacteria in the human intestine. The enzyme is a member of the haloalkanoate dehalogenase superfamily and represents a good model for the active-site protonation state of family members. Crystals of approximate dimensions 1.5 × 1.0 × 1.0 mm were obtained in space group P2(1)2(1)2, with unit-cell parameters a = 83.1, b = 108.9, c = 75.7 Å. A complete neutron data set was collected from a medium-sized H/D-exchanged crystal at BIODIFF at the Heinz Maier-Leibnitz Zentrum (MLZ), Garching, Germany in 18 d. Initial refinement to 2.3 Å resolution using only neutron data showed significant density for catalytically important residues.