Maier-Leibnitz Zentrum Research Articles

Prompt gamma rays of lanthanum and praseodymium produced by inelastic scattering of fission neutrons

AbstractEmission of prompt gamma rays in lanthanum and praseodymium nuclei triggered by (n,n’γ) inelastic scattering reactions of fission neutrons was investigated with the instrument FaNGaS (Fast Neutron-induced Gamma-ray Spectrometry) at Heinz Maier-Leibnitz Zentrum (MLZ). We identified 125 gamma lines (54 for lanthanum and 71 for praseodymium), for which we give the relative intensities and production cross sections. Presence of oxygen and chlorine in the samples was exploited to verify previous measurements. Our results are consistent with available literature data but also enhance it as we detect new lines and recognize a few false assignments. In addition, for a counting time of 12 h we estimated the detection limits of lanthanum and praseodymium as 0.6 and 0.4 mg, respectively.

Prompt gamma rays from fast neutron induced reactions on cerium and chlorine

Prompt gamma rays of cerium and chlorine were investigated with the FaNGaS (Fast Neutron-induced Gamma-ray Spectrometry) instrument operated at the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching. The gamma radiation was emitted from (n,n’), (n,p) and (n,α) reactions induced by the irradiation of a cerium(III) chloride (CeCl3) sample with a beam of fission neutrons. Additionally, a polyvinylchloride (PVC, (C2H3Cl)n) sample was irradiated to verify possible interferences between gamma lines of cerium and chlorine. We identified 87 prompt gamma lines of cerium and chlorine. From these, we assigned 58 lines to the (n,n’) reaction in cerium (one for 136Ce, 41 for 140Ce and 16 for 142Ce), 23 to the (n,n’) reaction in chlorine (15 for 35Cl and 8 for 37Cl), 5 lines to the 35Cl(n,p)35S reaction and 1 line to the 35Cl(n,α)32P reaction. We present relative intensities and fast-neutron spectrum-averaged partial cross sections of the aforementioned gamma lines and compare them with available literature data. Identification of new lines and discussion of possible errors adds important value to the literature data found to be consistent with our results. In addition, for a counting time of 12 h we estimate the detection limits for cerium and chlorine as 1 and 2 mg, respectively.

Fast neutron induced gamma rays from (n,n’), (n,p) and (n,α) reactions on CaCO3

Emission of prompt gamma rays following (n,n’), (n,p) and (n,α) reactions induced by irradiation of a calcium carbonate (CaCO3) sample with a beam of fission neutrons was investigated with a modified version of the FaNGaS (Fast Neutron-induced Gamma-ray Spectrometry) instrument operated at the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching. The neutron spectrum has an average energy of 2.30 MeV and at sample position the fast neutron flux was (1.13 ± 0.04) × 108 cm−2 s−1. The measurement was performed at an angle of 90° between neutron beam and detector. In total, we claim the identification of 38 prompt gamma lines, from which we have assigned 12 to the (n,n’) reaction in calcium (7 for 40Ca, 1 for 42Ca and 4 for 44Ca), 1 to the 12C(n,n’)12C reaction, and 2 to the (n,n’) reaction in oxygen (1 for 16O and 1 for 18O). The other observed gamma lines are attributed to the 40Ca(n,p)40K reaction (20 lines) and to the 40Ca(n,α)37Ar reaction (3 lines). Relative intensities and fast neutron spectrum averaged partial cross sections of the gamma lines are presented and compared with available literature data. Our results were found to be in good agreement with available literature data but also improved and complemented it, as we have pointed out possible errors and identified new lines. Additionally, for a counting time of 12 h the detection limits of calcium, carbon and oxygen were determined as 5, 13 and 64 mg, respectively.

Stable Metal–Halide Perovskite Colloids in Protic Ionic Liquid

Stable Metal–Halide Perovskite Colloids in Protic Ionic Liquid

Detection of hydrate plugs inside submarine pipelines using neutrons

ABSTRACT The objective of this study was to demonstrate the feasibility of localising and detecting hydrate plugs inside submarine pipelines, in situ and contactless, using neutron-induced analytical techniques. Cold and fast neutron-beam instruments at Heinz Maier-Leibnitz Zentrum (MLZ) were used to show that neutrons penetrate through the thick wall and the insulation of such pipes and even the induced gamma radiation can be detected outside to perform a non-destructive chemical analysis within the pipe. It was found that the change in the hydrogen concentration caused by a possible hydrate plug can be detected in seconds; while with a detailed analysis at a given spot lasting for a few hours, it is possible to unambiguously identify the hydrate phase inside the hydrocarbon phase.

Flexible Sample Environment for the Investigation of Soft Matter at the European Spallation Source: Part II—The GISANS Setup

The FlexiProb project is a joint effort of three soft matter groups at the Universities of Bielefeld, Darmstadt, and Munich with scientific support from the European Spallation Source (ESS), the small-K advanced diffractometer (SKADI) beamline development group of the Jülich Centre for Neutron Science (JCNS), and the Heinz Maier-Leibnitz Zentrum (MLZ). Within this framework, a flexible and quickly interchangeable sample carrier system for small-angle neutron scattering (SANS) at the ESS was developed. In the present contribution, the development of a sample environment for the investigation of soft matter thin films with grazing-incidence small-angle neutron scattering (GISANS) is introduced. Therefore, components were assembled on an optical breadboard for the measurement of thin film samples under controlled ambient conditions, with adjustable temperature and humidity, as well as the optional in situ recording of the film thickness via spectral reflectance. Samples were placed in a 3D-printed spherical humidity metal chamber, which enabled the accurate control of experimental conditions via water-heated channels within its walls. A separately heated gas flow stream supplied an adjustable flow of dry or saturated solvent vapor. First test experiments proved the concept of the setup and respective component functionality.

Flexible Sample Environment for the Investigation of Soft Matter at the European Spallation Source: Part II—The GISANS Setup

The FlexiProb project is a joint effort of three soft matter groups at the Universities of Bielefeld, Darmstadt, and Munich with scientific support from the European Spallation Source (ESS), the small-K advanced diffractometer (SKADI) beamline development group of the Julich Centre for Neutron Science (JCNS), and the Heinz Maier-Leibnitz Zentrum (MLZ).Within this framework, a flexible and quickly interchangeable sample carrier system for small-angle neutron scattering (SANS) at the ESS was developed. In the present contribution, the development of a sample environment for the investigation of soft matter thin films with grazing-incidence small-angle neutron scattering (GISANS) is introduced. Therefore, components were assembled on an optical breadboard for the measurement of thin film samples under controlled ambient conditions, with adjustable temperature and humidity, as well as the optional in situ recording of the film thickness via spectral reflectance. Samples were placed in a 3D-printed spherical humidity metal chamber, which enabled the accurate control of experimental conditions via water-heated channels within its walls. A separately heated gas flow stream supplied an adjustable flow of dry or saturated solvent vapor. First test experiments proved the concept of the setup and respective component functionality.

Prompt gamma rays induced by inelastic scattering of fission neutrons on iron

Prompt gamma rays induced by (n,n′γ) reactions on iron were measured with the instrument FanGaS (Fast Neutron induced Gamma-Ray Spectrometry) operated at the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching. The measurement was performed at an angle of 90° between neutron beam and detector. The fast neutron flux at the sample position was determined to be 1.40 × 108 cm−2 s−1 by using the foil activation method. Energies, relative intensities and fast neutron spectrum averaged isotopic cross section for production of 81 prompt gamma lines are presented. The results obtained are found in good agreement with literature data. The new set of gamma lines is recommended to replace the old dataset with several new lines also recognizing a few false identifications. This work is an important step towards the future chemical analysis of large samples at FanGaS employing highly penetrating fission neutrons.

Performance of a Position-Sensitive Neutron Scintillation Detector Based on Silicon Photomultipliers

In recent years, the price increase of 3He has triggered the search for alternative neutron detectors. One of the viable options is a scintillation-based neutron detector. Usually, photomultiplier tubes (PMTs) are used in these detectors for photodetection. However, the increase in performance requirements such as the operability in magnetic field and spatial resolution necessitates an advanced neutron detector. Therefore, we developed a detector prototype with an active area of 13 cm $\times\,13$ cm using silicon photomultipliers (SiPMs). As compared to PMTs, SiPMs offer more compactness, more robustness, and a lower sensitivity to magnetic field. The final detector is aimed to be used in the future at the TREFF instrument of the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching, Germany, for neutron reflectometry (NR). First measurements were carried out at TREFF and at the dedicated detector test instrument V17 at BER-II of HZB in Berlin, Germany. In this study, we report the results for detection efficiency, gamma discrimination, 2-D position resolution, count rate, and detection linearity.

Timing resolution of SiPM technologies before and after neutron irradiation

In recent years, silicon photomultiplier (SiPM) technology has been getting attention from various applications due to its low cost, immunity to magnetic field, compactness and ruggedness. However, its applicability in experiments with harsh radiation environments is still limited due to lack of corresponding radiation damage studies. A 10-year lifetime operation in a typical Small Angle Neutron Scattering (SANS) experiment with an acceptable degradation in photon detection efficiency has already been reported. In this article, we discuss the feasibility study of SiPM technology in neutron time of flight experiments. For this purpose, two analog SiPMs, developed by SensL and Hamamatsu, have been irradiated with cold neutrons (5 Å ) up to a dose of 6⋅1012 n/cm2 at the KWS-1 instrument of the Heinz Maier-Leibnitz Zentrum (MLZ) in Germany. After irradiation, the timing resolutions of the SiPMs have been measured under pulsed laser beam with a few hundred photons (405 nm) per pulse, and a degradation of up to 6 ps has been observed. The degradation might be a result of noise increase, introduced by surface defects caused by neutron exposure damage. Additionally, variation of the excess voltage helped to reveal the difference in the timing resolutions between irradiated and non-irradiated SiPMs, which remained almost constant.

Neutron MIEZE spectroscopy with focal length tuning

We report on a method to tune the focal length of high resolution neutron MIEZE spectrometers. The MIEZE technique relies on a fast sinusoidal neutron intensity modulation up to the MHz range, generated by the rotation of the neutron spin in radio-frequency spin flippers, and subsequent conversion to an intensity modulation by a spin analyzer. This intensity modulation is washed out due to the neutron velocity dispersion, but by proper choice of the spin rotation frequencies as well as the distances between sample, detector and spin flippers, a focal point in space appears (echo point), where the neutron detector is placed. In this work, we describe how to extend the dynamic range of the MIEZE technique by several orders of magnitude by introducing a field subtraction coil (NSE coil), such that at low energy resolution a good overlap with conventional spectroscopy techniques is achieved. All formulas for calculating the tuning parameters and an experimental example from the RESEDA spectrometer at the Heinz Maier–Leibnitz Zentrum (MLZ) are discussed.

Setup for polarized neutron diffraction using a high-Tc superconducting magnet on the instrument POLI at MLZ and its applications

A new polarized neutron diffraction setup has been developed for the hot neutron single crystal diffractometer POLI at the Maier-Leibnitz Zentrum (MLZ) in Germany. This setup consists of a 3He spin filter cell for polarization, a Mezei type double coil flipper optimized for short-wavelength neutrons, and a new high-Tc superconducting magnet producing fields up to 2.2 T. Because the magnet provides a symmetric field configuration, a dedicated guide field system was designed in order to avoid neutron depolarization in the zero-field node. The polarization transport efficiency of the whole setup was numerically simulated and optimized using COMSOL Multiphysics®. The polarization losses between the polarizer and the sample were confirmed to be smaller than 1.5% over the total field range of the magnet and the stray fields of the magnet did not affect the relaxation time T1 of the 3He spin filter polarizer. First experiments with antiferromagnetic and paramagnetic samples using the new setup have been successfully performed. Using the CCSL software, a reconstruction of the field induced spin density distribution in the weak ferromagnet MnCO3 was performed in the paramagnetic state. Our results show the high performance and good resolution of the new setup.

Study of gamma ray transitions and level scheme of [formula omitted] using the [formula omitted](nth,2γ) reaction

This work provides new data about the level scheme of Mn2556 studied by the Mn2555(nth,2γ) reaction. The spectroscopic information were collected using the gamma-gamma coincidence spectrometer at the Technische Universität München, Heinz Maier-Leibnitz Zentrum (MLZ), Garching, Germany. The intensities, energies of primary and secondary transitions of 71 energy-resolved cascades, as well as intermediate cascade levels were determined. The updated level scheme of Mn2556 was obtained from analyzing the intensity spectra of the strongest cascades. The comparison with the existing data in the ENSDF database shows that 23 primary transitions, 24 intermediate cascades levels as well as 32 secondary transitions determinated in this work can be recommended as new nuclear data.

The longitudinal neutron resonant spin echo spectrometer RESEDA

The instrumental layout and technical realisation of the neutron resonant spin echo (NRSE) spectrometer RESEDA at the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching, Germany, is presented. RESEDA is based on a longitudinal field configuration, boosting both dynamic range and maximum resolution of the spectrometer compared to the conventional transverse layout. The resonant neutron spin echo technique enables the realisation of two complementary implementations: A longitudinal NRSE (LNRSE) option comparable to the classical neutron spin echo (NSE) method for highest energy resolution and large momentum transfers as well as a Modulation of Intensity with Zero Effort (MIEZE) option for depolarising samples or sample environments such as high magnetic fields, and strong incoherent scattering samples. With their outstanding dynamic range, exceeding nominally seven orders of magnitude, both options cover new fields for ultra-high resolution neutron spectroscopy in hard and soft condensed matter systems. In this paper the concept of RESEDA as well as the technical realisation along with reference measurements are reported.

J-NSE-Phoenix, a neutron spin-echo spectrometer with optimized superconducting precession coils at the MLZ in Garching.

A novel set of superconducting main precession coils has been built and installed in the Jülich-neutron spin-echo (J-NSE) spectrometer at the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching. These unique new coils comprise a field-integral optimizing field shape, fringe field compensation, and high stability. They yield an enhancement of a factor of 2.5 in the intrinsic field-integral homogeneity, i.e., the resolution. The coil concept has been developed for the ESSENSE instrument proposal for the European Spallation Source. We report on the construction of and on the first results from the new superconducting neutron spin-echo spectrometer at the MLZ in Garching where the coils are the main part of a refurbishment of the J-NSE spectrometer after twenty years of operation.

Neutron and X-ray crystal structures of Lactobacillus brevis alcohol dehydrogenase reveal new insights into hydrogen-bonding pathways.

Lactobacillus brevis alcohol dehydrogenase (LbADH) is a well studied homotetrameric enzyme which catalyzes the enantioselective reduction of prochiral ketones to the corresponding secondary alcohols. LbADH is stable and enzymatically active at elevated temperatures and accepts a broad range of substrates, making it a valuable tool in industrial biocatalysis. Here, the expression, purification and crystallization of LbADH to generate large, single crystals with a volume of up to 1 mm3 suitable for neutron diffraction studies are described. Neutron diffraction data were collected from an H/D-exchanged LbADH crystal using the BIODIFF instrument at the Heinz Maier-Leibnitz Zentrum (MLZ), Garching, Germany to a resolution dmin of 2.15 Å in 16 days. This allowed the first neutron crystal structure of LbADH to be determined. The neutron structure revealed new details of the hydrogen-bonding network originating from the ion-binding site of LbADH and provided new insights into the reasons why divalent magnesium (Mg2+) or manganese (Mn2+) ions are necessary for its activity. X-ray diffraction data were obtained from the same crystal at the European Synchrotron Radiation Facility (ESRF), Grenoble, France to a resolution dmin of 1.48 Å. The high-resolution X-ray structure suggested partial occupancy of Mn2+ and Mg2+ at the ion-binding site. This is supported by the different binding affinity of Mn2+ and Mg2+ to the tetrameric structure calculated via free-energy molecular-dynamics simulations.

The new neutron depth profiling instrument N4DP at the Heinz Maier-Leibnitz Zentrum

The cold neutron guide of the Prompt Gamma Activation Analysis (PGAA) instrument (Revay et al. 2015) at the Heinz Maier-Leibnitz Zentrum (MLZ) provides an excellent opportunity for neutron depth profiling (NDP) due to its high collimated neutron flux. We present the concept, layout and first measurements with the new N4DP facility set-up at this beamline. A special focus is put on background analysis and instrument characterization. We present measurements of a NIST reference sample and of boron-containing float glasses which are used for neutron optical waveguides. We give an outlook concerning the ongoing development of position-resolved NDP using silicon microstrip detectors.

Energy research with neutrons (ErwiN) and installation of a fast neutron powder diffraction option at the MLZ, Germany.

The need for rapid data collection and studies of small sample volumes in the range of cubic millimetres are the main driving forces for the concept of a new high-throughput monochromatic diffraction instrument at the Heinz Maier-Leibnitz Zentrum (MLZ), Germany. A large region of reciprocal space will be accessed by a detector with sufficient dynamic range and microsecond time resolution, while allowing for a variety of complementary sample environments. The medium-resolution neutron powder diffraction option for 'energy research with neutrons' (ErwiN) at the high-flux FRM II neutron source at the MLZ is foreseen to meet future demand. ErwiN will address studies of energy-related systems and materials with respect to their structure and uniformity by means of bulk and spatially resolved neutron powder diffraction. A set of experimental options will be implemented, enabling time-resolved studies, rapid parametric measurements as a function of external parameters and studies of small samples using an adapted radial collimator. The proposed powder diffraction option ErwiN will bridge the gap in functionality between the high-resolution powder diffractometer SPODI and the time-of-flight diffractometers POWTEX and SAPHiR at the MLZ.

Photodetection Characterization of SiPM Technologies for their Application in Scintillator based Neutron Detectors

Small-angle neutron scattering (SANS) experiments have become one of the most important techniques in the investigation of the properties of material on the atomic scale. Until 2001, nearly exclusively 3He-based detectors were used for neutron detection in these experiments, but due to the scarcity of 3He and its steeply rising price, researchers started to look for suitable alternatives. Scintillation based solid state detectors appeared as a prominent alternative. Silicon photomultipliers (SiPM), having single photon resolution, lower bias voltages compared to photomultiplier tubes (PMT), insensitivity to magnetic fields, low cost, possibility of modular design and higher readout rates, have the potential of becoming a photon detector of choice in scintillator based neutron detectors. The major concerns for utilizing the SiPM technology in this kind of applications are the increase in their noise performance and the decrease in their photon detection efficiency (PDE) due to direct exposure to neutrons. Here, a detailed comparative analysis of the PDE performance in the range between UV and NIR parts of the spectra for three different SiPM technologies, before and after irradiation with cold neutrons, has been carried out. For this investigation, one digital and two analog SiPM arrays were irradiated with 5Å wavelength cold neutrons and up to a dose of 6×1012 n/cm2 at the KWS-1 instrument of the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching, Germany.

Neutron imaging with fission and thermal neutrons at NECTAR at MLZ

The instrument NECTAR is located at beam port SR10 of the neutron source FRM II at the Heinz Maier-Leibnitz Zentrum (MLZ). With a pair of moveable uranium plates placed in front of the entrance window of the beam tube, a fission neutron spectrum with a mean energy of 1.9 MeV can be used for neutron imaging applications. Via remote control these plates can be removed and a thermal neutron spectrum (mean energy at 28 meV) gets available for experiments. While the fission neutron spectrum is regularly used, some upgrades of the instrument are necessary to make the thermal neutron spectrum routinely available for user experiments. This includes additional equipment like a new sample stage and a second detector system foreseen to extend the capabilities of NECTAR. The current state of the instrumentation and necessary changes for the future thermal beam option and its usage for standard user experiments will be presented. First measurements were carried out with a temporary flight tube installed and a compact detector (510 mm × 180 mm x 180 mm) for thermal neutrons with a spatial resolution in the range of 100 μm. The feasibility of the thermal beam option could already be verified at an L/D ratio of 240 and a thermal neutron flux of 7.92·106 cm−2 s−1. The thermal neutron beam option adds a pure thermal neutron spectrum – Maxwell spectrum originating from the moderator without alteration by a secondary source or converter – to the energy ranges available for neutron imaging at MLZ instruments. It also offers a unique possibility to combine two quite different neutron energy ranges at a single instrument including their respective advantages. The thermal neutron beam option is funded by BMBF in the frame of research project 05K16VK3.