Showing papers in "Neutron News in 2005"
TL;DR: In this article, the authors consider the problem of small-angle neutron scattering (SANS) experiments and show that the dynamic range of SANS instruments is usually determined by the size of the detector, which is limited mainly by technical reasons and the wavelength range of available thermal neutrons in the neutron beam.
Abstract: Most of the objects of small-angle neutron scattering (SANS) experiments require the measurements of a studied sample in a wide range of momentum transfer (Q-range). Larger Q-range means more reliable determination of a model of the investigated material as well as higher accuracy of its calculated structural parameters. The dynamic range of SANS instruments is normally determined by the size of the detector, which is limited mainly by technical reasons and by the wavelength range of available thermal neutrons in the neutron beam. Even in the case of the largest detector (1 m2) at one of the best beam lines—the D22 instrument at ILL—the dynamic range is about 50. Usually the problem of the Qrange is solved by a sequence of measurements with the detector at different positions. However, it leads to considerable increase in the data acquisition time. Moreover, the problem becomes critical when it is necessary to study processes in real time, especially irreversible processes.
149 citations
TL;DR: In this article, the authors used a counter-rotating pair of fast disc choppers for short-pulse spallation neutron sources (SPS) to shorten the pulse width.
Abstract: High-resolution time-of-flight (TOF) diffractometers at short-pulse spallation neutron sources (SPS)—the most well-known example is HRPD at ISIS—have proved themselves to be extremely good for various applications. The resolution, R = Δd/d, close to 0.001 or even a bit better, can be easily obtained if a flight path amounts to 50-100 meters. But at so-called “long pulse sources” (LPS), with the pulse width Δt 0 equal to hundreds of microseconds, the flight path would need to be too long if a 0.001 resolution level is required. In this case, effective shortening of the neutron pulse should be done by employing a counter-rotating pair of fast disc choppers (see, for instance, Ref. [1]) or the correlation Fourier technique.
102 citations
TL;DR: In spite of competing non-nuclear analytical techniques (AAS, ICP-ES and ICPMS), NAA continues to be the most powerful multi-element analytical technique used in geosciences, life sciences, and materials science as discussed by the authors.
Abstract: In spite of competing non-nuclear analytical techniques (AAS, ICP-ES, ICP-MS, etc.), reactor neutron activation analysis (NAA) continues to be the most powerful multi-element analytical technique used in geosciences, life sciences, and materials science. Non-destructive NAA, being a technique based on a physical principle different from those of other trace element techniques, should always be used, if feasible, when the need for better quantification of trace elements at ultra-low levels is desirable. In the certification of reference material, NAA as an accurate technique has played and is still playing a key role, even for elements where other techniques have replaced NAA in practical work.
34 citations
TL;DR: In this article, Bonse-Hart cameras (double crystal diffractometers) are used for U-SANS experiments, whereas the standard SANS experiment is performed using a pinhole camera.
Abstract: Ultra-small angle (U-SANS) and small angle neutron scattering (SANS) experiments are performed by two different types of instruments to cover a combined Q-range from ≈10−5A−1 up to ≈1A−1. Bonse-Hart cameras (double crystal diffractometers) are used for U-SANS experiments, whereas the “standard” SANS experiment is performed using a pinhole camera. In principle, the Q-range of both instrument classes overlaps. Typical U-SANS instruments like S18 (ILL), PCD (NIST), or DKD (FZJ) may reach maximum Q-vectors of ≈5 × 10−3. The disadvantage of these instruments is that they do not allow taking a full area image on a 2D position sensitive detector. On the other hand, the well-known pinhole instrument D11 at Institut Laue-Langevin (France) reaches a minimum Q-vector of 5 × 10−4A−1 by use of large wavelengths and sample-to-detector distances (≈40m).
19 citations
TL;DR: The J-PARC project has been in progress concerning the construction of experimental facilities along with high intensity proton accelerators, aimed at scientific breakthroughs in materials and life sciences, nuclear and elementary physics research, and the technological development of an accelerator-driven transmutation system as discussed by the authors.
Abstract: The J-PARC project has been in progress concerning the construction of experimental facilities along with high intensity proton accelerators, aimed at scientific breakthroughs in materials and life sciences, nuclear and elementary physics research, and the technological development of an accelerator-driven transmutation system [1]. Most of the 3–GeV protons are extracted to be injected into a facility called the Materials and Life Science Experimental Facility (MLF), in which a 1-MW pulse neutron source (JSNS) and a muon production target are located, sharing the beam in tandem fashion [2]. A neutron beam with high performance of time resolution, along with high intensity in the 1-MW regime, will open realistic technological breakthroughs in the sciences of microscopic molecular dynamics; surface physics, magnetism; polymer; biology; structure and its functions; precise methods for analysis; dynamic visualization techniques; many industrial applications; and even evolution in cosmology and astrophysics.
16 citations
TL;DR: In this article, the authors describe the use of Microstrip Gas Counters (MSGCs) as an acceptable compromise between performance and cost, explaining why the demand for the MSGC has remained rather low in a majority of applications.
Abstract: Multiwire Proportional Chambers (MWPC) and scintillators coupled to photo-multiplier tubes are the two main techniques currently used for accurate position-sensitive detectors in thermal neutron instrumentation. They fulfill the instrumental requirements for most applications and are accessible to many neutron institutes in terms of the manpower and equipment required for maintenance and technical development. Microstrip Gas Counters (MSGC), introduced in 1988 [1], work on the same principle as MWPCs, with the intrinsic advantage of a higher counting rate and better spatial resolution. Approximately ten instruments at the ILL are using MSGCs, the largest one being operational on the D20 powder diffractometer since September 2000 [2]. Two other European neutron institutes, PSI and RISO, have also used MSGCs [3]. In many situations, the Multiwire Proportional Chamber offers an acceptable compromise between performance and cost, explaining why the demand for the MSGC has remained rather low in a majority of ...
12 citations
TL;DR: In this paper, the first successful experiments performed using diamond anvil cells in the 0-31GPa range were performed using inelastic neutron scattering in the presence of high pressure.
Abstract: High-pressure research plays an important role in modern condensed matter physics and is attracting the growing interest of researchers. Pressure-induced changes of interatomic and magnetic interactions in materials often lead to structural and magnetic phase transitions and consequent drastic changes in their macroscopic properties. Neutron diffraction and inelastic neutron scattering investigations provide an invaluable insight into the nature of the different pressure-induced phenomena in materials. Due to a relatively small intensity of neutron sources, typical sample volumes required for a neutron scattering experiment are about cm3 and the attainable pressure range has been restricted to only about 03 GPa for a long time. Since the first successful experiments performed using diamond anvil cells in the 0-31GPa range
9 citations
TL;DR: In this paper, the first neutron reflectometry experiments were carried out at FLNP JINR (Dubna, Russia), where the authors measured the magnetic field penetration depth into a superconducting film on the polarized neutron spectrometer SPN at the IBR-2 fast-pulsed reactor of periodic operation.
Abstract: At FLNP JINR (Dubna, Russia), the first neutron reflectometry experiments were carried out to measure the magnetic field penetration depth into a superconducting film on the polarized neutron spectrometer SPN at the IBR-2 fast-pulsed reactor of periodic operation by D.A. Korneev and colleagues, in 1988, after the reactor was put in operation [1]. Later on, SPN-aided investigations were conducted on thin films (2), including superconducting ones (3), on magnetic multilayers (4), and on interfaces in the structure Fe/V at room temperature (5) and at temperatures below the superconducting transition temperature of vanadium (6).
9 citations
TL;DR: The normal component in gas-filled neutron detectors was for many years boron trifluoride, BF3, but in recent years 3He has become the converter gas of choice.
Abstract: The normal component in gas-filled neutron detectors was for many years boron trifluoride, BF3, but in recent years 3He has become the converter gas of choice. Although 3He is expensive (about €90 per liter), it is a better proportional counter gas, particularly with respect to electron multiplication, and has a higher conversion efficiency per molecule than BF3
6 citations
TL;DR: The DNS instrument as mentioned in this paper is a time-of-flight instrument with a multi-detector system similar to the D7 instrument at the ILL, which is particularly devoted to elastic and inelastic diffuse scattering that may arise from shortrange correlations and disorder in materials.
Abstract: The neutron’s magnetic moment is an ideal probe to study magnetic structures and excitations in condensed matter physics. Polarization analysis gives valuable additional information and such vector properties. Of course, one should not forget interesting applications to soft matter physics by separating coherent and spin-incoherent scattering, particularly from the large cross-section of hydrogen, and applications in combination with H/D isotope labeling and contrast variation. Figure 1 shows an example of such an experiment done at the DNS instrument at Julich. This type of instrument with medium resolution is particularly devoted to elastic and inelastic diffuse scattering that may arise from short-range correlations and disorder in materials. A layout of the instrument is shown in Figure 2. DNS is a time-of-flight instrument [2] with a multi-detector system similar to the D7 Instrument at the ILL [3]. The monochromatic incident beam is polarized with a focusing supermirror bender, the guide field aroun...
4 citations
TL;DR: In this article, two detector types, i.e., silicon microstrip (Si-MSD) and hybrid microstrip gas chamber (MSGC) detectors, are described, both using thin 157Gd converters and aiming at two-dimensional position resolutions of 50-100 μm FWHM, pulse-height readout for centerof-gravity calculation and background suppression, time-of-flight (TOF) resolution <<1 μs, and counting rate capacity of 108 events/s per detector module with single event counting.
Abstract: In the current (2004-2008) Joint Research Activity DETNI (Detectors for Neutron Instrumentation) in the EU Integrated Infrastructure Initiative for Neutron Scattering and Muon Spectroscopy (NMI3), three detector types and a common ASIC and data acquisition board family are being developed. Two of these detector types, i.e., silicon microstrip (Si-MSD) and hybrid microstrip gas chamber (MSGC) detectors, are described in this article, both using thin 157Gd converters and aiming at two-dimensional position resolutions of 50-100 μm FWHM, pulse-height readout for center-of-gravity calculation and background suppression, time-of-flight (TOF) resolution <<1 μs, and a counting rate capacity of 108 events/s per detector module with single event counting. The third detector type is the CASCADE detector discussed in the another article.
TL;DR: The Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research in Dubna (located about 130 km north of Moscow) was created in 1956 and the first IBR facility was put into operation in 1960 as discussed by the authors.
Abstract: The Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research in Dubna (located about 130 km north of Moscow) was created in 1956. The laboratory got its name after the late Professor I.M. Frank, Nobel Prize Laureate and first director of the laboratory. To develop scientific activity in neutron physics, it was decided to construct a pulsed reactor with periodic operation. This idea was realized in 1960, when the first IBR facility was put into operation. The average power of this reactor was just 1 kW, but the power in the pulse reached 5 MW.
TL;DR: The Frank Laboratory of Neutron Physics (FLNP) of the Joint Institute for Nuclear Research in Dubna, Russia as mentioned in this paper has developed ingenious instrumentations such as the Fourier diffractometer, the twodetector system for SANS-experiments, an instrument dedicated to high-pressure studies, and a polarized reflectometer, whose descriptions can be found in the present issue.
Abstract: The current issue of Neutron News features the Frank Laboratory of Neutron Physics (FLNP) of the Joint Institute for Nuclear Research in Dubna, Russia. Since we recently had presentations of both steady-state reactors and pulsed spallation sources, I decided that it was time to describe the advances realized at the only running pulsed-reactor. Because of the peculiar time-structure of the neutron beam produced by such a source, scientists at FLNP had to develop ingenious instrumentations such as the Fourier diffractometer, the twodetector system for SANS-experiments, an instrument dedicated to high-pressure studies, and a polarized reflectometer, whose descriptions can be found in the present issue.
TL;DR: The J-PARC JSNS target station is a 1MW source and will receive 333μA of 3-GeV protons as discussed by the authors, which will have a width of 1μs and a repetition rate of 25-Hz.
Abstract: The J-PARC JSNS target station is a 1-MW source and will receive 333μA of 3-GeV protons. The proton pulse will have a width of 1μs and a repetition rate of 25-Hz. Those parameters for the accelerator have been well considered from neutron experimental points of view, and will provide a very high performance and uniqueness concerning the instrument suite at JSNS. The repetition rate of 25-Hz will give a wide dynamical range in one frame for time-of-flight measurements and a high impulse intensity for each neutron burst. The repetition rate of 25-Hz is a great compromise to satisfy both high-energy spectroscopy and slow-neutron experiments, and is also good for high-resolution instruments with long flight paths.
TL;DR: Laterally patterned magnetic structures are systems that are structured, in addition, along a second (nanostripes) or third (nanodots) dimension Fundamentally, novel properties analogous to the interlayer exchange coupling and the giant magnetoresistance effect in magnetic multilayers can be expected if the size of the structures become comparable to or smaller than certain characteristic length scales, such as the spin diffusion length, carrier mean free path, magnetic domain wall width.
Abstract: While magnetic multilayers can be regarded as systems that are artificially structured along one dimension, laterally patterned magnetic structures are systems that are structured, in addition, along a second (nanostripes) or third (nanodots) dimension Fundamentally, novel properties analogous to the interlayer exchange coupling and the giant magnetoresistance effect in magnetic multilayers can be expected if the size of the structures become comparable to or smaller than certain characteristic length scales, such as the spin diffusion length, carrier mean free path, magnetic domain wall width, etc [1] Typically, those length scales lie in the several-to-hundreds nm range
TL;DR: In this article, the authors define an interface layer between oil and water in a microemulsion, and the total area of this interface is basically given by the amount of surfactant, and for a given topology of the oil/water regions, it controls their dimensions.
Abstract: Microemulsions are thermodynamically stable dispersions of two otherwise non-miscible fluids—usually “oil” and “water”—that are mediated by a surfactant. The surfactant molecules have to be amphiphilic, i.e., one end of a molecule is soluble in oil and the other end in water. The surfactant forms an interface layer between oil and water in the microemulsion. The total area of this interface is basically given by the amount of surfactant, and for a given topology of the oil/water regions, it controls their dimensions.