31 research outputs found
Evaluation of a method for time-of-flight, wavelength and distance calibration for neutron scattering instruments by means of a mini-chopper and standard neutron monitors
Accurate conversion of neutron time-of-flight (TOF) to wavelength, and its
uncertainty, is of fundamental importance to neutron scattering measurements.
Especially in cases where instruments are highly configurable, the
determination of the absolute wavelength after any change must always be
performed. Inspired by the manner with which neutron spectrometers determine
the absolute wavelength, we evaluate for the first time, in the author's
knowledge, a commonly used method for converting TOF to neutron wavelength, the
distance of a monitor from the source of neutrons and we analytically calculate
the uncertainty contributions that limit the precision of the conversion. The
method was evaluated at the V20 test beamline at the Helmholtz Zentrum Berlin
(HZB), emulating the ESS source with a pulse of 2.86 ms length and 14 Hz
repetition rate, by using a mini-chopper operated at 140 Hz, beam monitors
(BMs) and data acquisition infrastructure. The mini-chopper created
well-defined neutron pulses and the BM was placed at two positions, enabling
the average wavelength of each of the pulses created to be determined. The used
experimental setup resulted in absolute wavelength determination at the monitor
positions with a of 1.8% for
\r{A}. With a modest increase of the distance between the
reference monitor positions a of below
0.5% can be achieved. Further improvements are possible by using a thinner
monitor, smaller chopper disc openings and a higher rotational speed chopper.
The method requires only two neutron measurements and doesn't necessitate the
use of crystals or complex fitting, and could constitute a suitable addition to
imaging, diffraction, reflectometers and small angle neutron scattering
instruments, at spallation sources, that do not normally utilise fast choppers
Effects of reactive oxygen species and neutrophils on endothelium-dependent relaxation of rat thoracic aorta
Reactive oxygen species (ROS) are produced in different metabolic processes including the respiratory burst of neutrophils accompanying local inflammation. The aim of this study was to analyze the effects of N-formyl-methionyl-leucyl-phenylalanine (FMLP)-activated neutrophils, isolated from the guinea pig peritoneal cavity, on isolated rings of a large (conduit) artery, the rat thoracic aorta. FMLP-activated neutrophils enhanced the basal tension increased by α1-adrenergic stimulation. In phenylephrine-precontracted aortae, they elicited marked contraction, while in noradrenaline-precontracted rat aortal rings they caused a biphasic response (contraction-relaxation). To eliminate interaction of activated neutrophils with catecholamines, in the subsequent experiments the basal tension was increased by KCl-induced depolarization. Activated neutrophils evoked a low-amplitude biphasic response (relaxation-contraction) on the KCl-induced contraction. Not only the acetylcholine- and A23187-induced relaxations but also the catalase sensitive hydrogen peroxide (H2O2) elicited contractions were endothelium-dependent. Even though the acetylcholine-induced relaxation was changed by activated neutrophils and by the ROS studied, their effects differed significantly, yet none of them did eliminate fully the endothelium-dependent acetylcholine relaxation. The effect of activated neutrophils resembled the effect of superoxide anion radical (O2
•–) produced by xanthine/xanthine oxidase (X/XO) and differed from the inhibitory effects of Fe2SO4/H2O2-produced hydroxyl radical (•OH) and H2O2. Thus O2
•– produced either by activated neutrophils or X/XO affected much less the endothelium-dependent acetylcholine-activated relaxation mechanisms than did •OH and H2O2. In the large (conduit) artery, the effects of activated neutrophils and various ROS (O2
•–, •OH and H2O2) seem to be more dependent on muscle tension than on endothelial mechanisms
Time- and energy-resolved effects in the boron-10 based Multi-Grid and helium-3 based thermal neutron detectors
The boron-10 based Multi-Grid detector is being developed as an alternative
to helium-3 based neutron detectors. At the European Spallation Source, the
detector will be used for time-of-flight neutron spectroscopy at cold to
thermal neutron energies. The objective of this work is to investigate fine
time- and energy-resolved effects of the Multi-Grid detector, down to a few
eV, while comparing it to the performance of a typical helium-3 tube.
Furthermore, it is to characterize differences between the detector
technologies in terms of internal scattering, as well as the time
reconstruction of ~ s short neutron pulses. The data were taken at the
Helmholtz Zentrum Berlin, where the Multi-Grid detector and a helium-3 tube
were installed at the ESS test beamline, V20. Using a Fermi-chopper, the
neutron beam of the reactor was chopped into a few tens of s wide pulses
before reaching the detector, located a few tens of cm downstream. The data of
the measurements show an agreement between the derived and calculated neutron
detection efficiency curve. The data also provide fine details on the effect of
internal scattering, and how it can be reduced. For the first time, the chopper
resolution was comparable to the timing resolution of the Multi-Grid detector.
This allowed a detailed study of time- and energy resolved effects, as well as
a comparison with a typical helium-3 tube.Comment: 37 pages, 21 figure
Neutron and X-Ray Diffraction of Ti-Ta and Co49Ni21Ga30 High-Temperature Shape-Memory-Alloys
Evolution of distance between omega particles in metastable beta Ti alloy determined from in situ small angle neutron scattering
The evolution of distance between omega particles in metastable beta Ti 15Mo alloy 8.1 in at. was determined from in situ small angle neutron scattering SANS . SANS data were recorded during heating of the material from room temperature to 600 C with the heating rate of 1 C min. The results agree with previously determined ordering of omega particles in a cubic three dimensional array with the axes along the cubic axes [100]beta of the host lattice. The distance between particles, which increases with temperature, was investigated in three orientations with the incident beam parallel to [100]beta, [110]beta and [111]bet