Berlin Neutron Scattering Center Research Articles

Rotational effect of fissile nucleus in binary fission of 235U induced by cold polarized neutrons

We have found a small inclination of the symmetry axis of the prompt fission gamma-quanta angular distribution relative to the “fission axis” in binary fission of 235U induced by cold polarized neutrons using the neutron beam line V13 at Berlin Neutron Scattering Center (BENSC). The sign of the shift depends on the direction of the cold neutron beam polarization and it can only be explained by the quasi-classical rotation of the fissile nucleus at the scission point.

Upgrade Program for the Cold Neutron Instrumentation of the Helmholtz-Zentrum Berlin

The Helmholtz-Zentrum Berlin (HZB, former Hahn-Meitner-Institut) operates more than 20 instruments at the medium-flux research reactor BER II, a modern neutron source which was completely renewed during the years 1985–1992. The creation of the Berlin Neutron Scattering Center (BENSC) in 1993 marked the beginning of an extended user program, offering access to a great variety of new instruments with some unique features suited for research in many fields of science. In the course of time the Helmholtz-Zentrum Berlin has established itself as a major neutron science facility with an exceptionally high demand from international, in particular European users.

New high field magnet for neutron scattering at Hahn-Meitner Institute

The Berlin Neutron Scattering Center BENSC at the Hahn-Meitner-Institute (HMI) is a user facility for the study of structure and dynamics of condensed matter with neutrons and synchrotron radiation with special emphasis on experiments under extreme conditions. Neutron scattering is uniquely suited to study magnetic properties on a microscopic length scale, because neutrons have comparable wavelengths and, due to their magnetic moment, they interact with the atomic magnetic moments. Magnetic interactions and magnetic phenomena depend on thermodynamic parameters like magnetic field, temperature and pressure. At HMI special efforts are being made to offer outstanding sample environments such as very low temperatures or high magnetic fields or combination of both. For the future a dedicated instrument for neutron scattering at extreme fields is under construction, the Extreme Environment Diffractometer ExED. For this instrument the existing superconducting magnets as well as a future hybrid system can be used. The highest fields, above 30 T will be produced by the planned series-connected hybrid magnet system, designed and constructed in collaboration with the National High Magnetic Field Laboratory, Tallahassee, FL.

Benefits of polarized small-angle neutron scattering on magnetic nanometer scale structure modeling

Recent use of polarized neutron technique in small-angle scattering (SANS) have led to impressive results in the case of magnetic nanometer-scale structure analysis. In some particular cases this method offers the possibility to survey structure models with the necessary accuracy for the first time. The different cross sections for spin-up and spin-down neutron scattering on magnetic precipitates can be combined with the method of chemical contrast variation. All data fitting using structure models will benefit of that kind of constraints. The analysis of the interference term of nuclear and magnetic scattering respectively enables the extraction of additional information about the composition and magnetization profiles of the samples. Here we place emphasis on the difference of spin-up and spin-down neutron scattering intensities to obtain this information. This technique profits by the clear distinction between magnetic and nonmagnetic scattering contributions and the strong auxiliary conditions for model fitting procedures. Depending on the relative orientations of the external magnetic field, the local magnetization of the precipitates and the scattering vector, significant scattering patterns can be scrutinized. Beside general formulas for some special cases of present experimental interest we exercise the approach to a nontrivial case of data obtained from polarised SANS experiments at the Berlin Neutron Scattering Center (BENSC).

Single-crystal neutron diffractometry — Recent developments and trends

Abstract An overview is given over recent developments and trends in single-crystal neutron diffractometry. Special emphasis is put on instrumental developments which have considerably enhanced the efficiency of neutron scattering experiments over the last years by improving monochromator and/or detector systems. Not discussed are developments in the field of polarised neutrons. Examples from the Berlin Neutron Scattering Center (BENSC) are given for the measurement of short-range magnetic order using the flat-cone diffractometer E2 of BENSC and of the study of long-range magnetic order making use of a high-field cryomagnet at BENSC. The perspectives of neutron diffractometry within the next 5 to 10 years are discussed with view on the new powerful spallation sources SNS (under construction in the United States), JSNS (under construction in Japan) and ESS, the European Spallation Source, planned to be constructed in Europe.

Peak shape at the axially focusing E9 powder diffractometer - theoretical and experimental description

The high-resolution neutron powder diffractometer E9 at the Berlin Neutron Scattering Center, HMI, uses an axially focusing monochromator in combination with a wide detector opening in order to optimize the intensity. Common descriptions of the asymmetry for this type of instrument consider the effects of the heights of sample and detector only. However, with an axial convergence angle of about 7° from the monochromator the effects caused by the high inclination of parts of the incoming beam have to be considered. An improved peak-shape model was tested taking into account these and additional minor effects.

HMI hosts second workshop on high magnetic fields for neutrons

Magnetic fields represent one of the three fundamental thermodynamic variables, besides temperature and pressure. To probe electronic and magnetic states in materials, among others, it is important to investigate a wide range of thermodynamic stability. This requirement challenges sample environments, which have evolved to be technologically sophisticated and expensive. The Berlin Neutron Scattering Center (BENSC) at the Hahn-Meitner-Institute (HMI) is well known among neutron scattering centers due to its availability of complex sample environment conditions that include the highest DC magnetic field for neutron scattering of 17 T.

E9: The New High-Resolution Neutron Powder Diffractometer at the Berlin Neutron Scattering Center

E9: The New High-Resolution Neutron Powder Diffractometer at the Berlin Neutron Scattering Center

Quasielastic neutron scattering from trehalose aqueous solutions

The work reports quasielastic neutron scattering (QENS) results on aqueous solutions of trehalose, a biologically and biomedically important disaccharide. We collected data at the Berlin Neutron Scattering Center (BENSC) on α,α-trehalose deuterated (C12H14O11D8) samples in D2O and on α,α-trehalose hydrogenated (C12H22O11) samples in H2O at different water content. The employment of selectively deuterated samples allows the separation of the diffusive dynamics of water from that of trehalose. The aim of the work is to furnish new results on the molecular dynamics of trehalose and to investigate the effect of this disaccharide on the neighboring water. This study is part of a comprehensive research effort to understand the molecular processes underlying the bio-protectant effectiveness of the disaccharide using plenty of physical techniques [light scattering, nuclear magnetic resonance (NMR), neutron scattering, thermodynamic measurements]. The data analysis furnishes a microscopic whole-molecule diffusion coefficient in good agreement with NMR results. Furthermore it results that the dynamics of the neighboring water is strongly affected by the presence of trehalose.

The berlin neutron scattering center (BENSC) at the Hahn-Meitner-Institut Berlin-a European facility

The upgraded Berlin Research Reactor BER2 of the Hahn-Meimer-Institut Berlin (HMI) started operation late in 1992. The neutron scattering instruments at the cold and thermal beam lines of thissource are available to internal and external users in the framework of BENSC. In January 2000, the step-by-step conversion (started in 1997) of BER2 from high enriched uranium fuel elements (HEU)to low enriched uranium elements (LEU) was completed.

Neutron time-of-flight measurement techniques: new possibilities of TOF spectroscopy with NEAT at BENSC

A series of experiments performed on the TOF spectrometer NEAT at the Berlin Neutron Scattering Center is reported to demonstrate the versatility and some of the original possibilities offered by this instrument: continuous variation of the energy resolution over four decades, TOF diffraction using single detectors and a large range of incident neutron wavelengths, high-resolution studies in (Q, ω) -space of single crystals with a multidetector at large scattering angle, or elastic and inelastic small-angle scattering with the multidetector at zero angle.

TOF diffraction experiments with NEAT at BENSC

We report on a series of experiments performed on the very flexible TOF spectrometer NEAT at the Berlin Neutron Scattering Center, which demonstrates one of the unusual possibilities offered by this instrument: TOF diffraction with incident neutron wavelengths up to at least 20 Å. This is especially suitable for studies of complex systems with large unit cells, as the structural characterization and inelastic scattering measurements can be carried out consecutively, without changing geometry and sample environment.

First QINS results from the TOF-spectrometer NEAT

First QINS results from the new high-resolution multichopper time-of-flight spectrometer NEAT at the Berlin Neutron Scattering Center (BENSC) are reported, together with a brief description of the instrument. The spectrometer performance is demonstrated with the aid of spectra from two different examples concerning 1. (i) the nature of the reorientational motion of molecules in plastic adamantane, and 2. (ii) a fast local diffusive motion apparently connected with the proton diffusion mechanism required for proton conduction in anhydrous zirconium phosphate.

NEAT experiments at BENSC

Abstract NEAT is a multichopper time-of-flight spectrometer for inelastic neutron scattering at medium and very low energy and momentum transfers, including inelastic small-angle scattering (e.g. quasielastic or Brillouin scattering). NEAT was commissioned early in 1995 and is in continuous operation for experiments at the Hahn-Meitner-Institut (HMI) since May 1995. Its basic conception is derived from that of the INS spectrometer at the Institut Laue-Langevin (ILL), Grenoble. The further development at the Berlin Neutron Scattering Center (BENSC) has, however, led to a number of modifications yielding a significant improvement of this type of instrument. As a result, the duration of an experiment with given energy resolution carried out with NEAT is quite comparable to that of a similar INS-experiment, in spite of the fact that the thermal neutron flux of the BER-II reactor at HMI is inferior to that of the Grenoble high-flux reactor by an order of magnitude.

Low temperature record for neutron scattering studies

Abstract At the Hahn-Meitner-Institut in Berlin, Germany, the first Bragg reflections from a nuclear antiferromagnetic state in silver have recently been observed. The results were obtained by an international research team, in an EC-supported collaboration between the Helsinki University of Technology, Finland, Ris⊘ National Laboratory, Denmark, and the Berlin Neutron Scattering Center at the Hahn-Meitner-Institut Berlin.