The response of a position-sensitive Li-glass scintillator detector being developed for thermal-neutron detection with 6 mm position resolution has been investigated using collimated beams of thermal ...neutrons. The detector was moved perpendicularly through the neutron beams in 0.5 to 1.0 mm horizontal and vertical steps. Scintillation was detected in an 8 × 8 pixel multi-anode photomultiplier tube on an event-by-event basis. In general, several pixels registered large signals at each neutron-beam location. The number of pixels registering signal above a set threshold was investigated, with the maximization of the single-hit efficiency over the largest possible area of the detector as the primary goal. At a threshold of ∼50% of the mean of the full-deposition peak, ∼80% of the events were registered in a single pixel, resulting in an effective position resolution of ∼5 mm in X and Y. Lower thresholds generally resulted in events demonstrating higher pixel multiplicities, but these events could also be localized with ∼5 mm position resolution.
Self-assembled structures having a regular hollow icosahedral form (such as those observed for proteins of virus capsids) can occur as a result of biomineralization processes, but are extremely rare ...in mineral crystallites. Compact icosahedra made from a boron oxide have been reported, but equivalent structures made of synthetic organic components such as surfactants have not hitherto been observed. It is, however, well known that lipids, as well as mixtures of anionic and cationic single chain surfactants, can readily form bilayers that can adopt a variety of distinct geometric forms: they can fold into soft vesicles or random bilayers (the so-called sponge phase) or form ordered stacks of flat or undulating membranes. Here we show that in salt-free mixtures of anionic and cationic surfactants, such bilayers can self-assemble into hollow aggregates with a regular icosahedral shape. These aggregates are stabilized by the presence of pores located at the vertices of the icosahedra. The resulting structures have a size of about one micrometre and mass of about 1010 daltons, making them larger than any known icosahedral protein assembly or virus capsid. We expect the combination of wall rigidity and holes at vertices of these icosahedral aggregates to be of practical value for controlled drug or DNA release.
Neutron focusing leads to significant gains in flux‐on‐sample in small‐angle neutron scattering and very small angle neutron scattering instruments. Understanding the out‐of‐focus condition is ...necessary for less than optimal conditions such as for short instruments and low neutron wavelengths. Neutron focusing is investigated using a three‐pronged approach. The three methods are analytical calculations, resolution measurements and computer simulations. A source aperture containing a single small‐size hole and a sample aperture containing multiple holes are used to produce multiple spots on the high‐resolution neutron detector. Lens focusing elongates off‐axis spots in the radial direction. The standard deviation for the size of each spot is estimated using these three approaches. Varying parameters include the neutron wavelength, the number of focusing lenses and the location of holes on the sample aperture. Enough agreement for the standard deviation of the individual neutron beams was found between the calculations and the measurements to give confidence in this approach. Good agreement was found between the standard deviations obtained from calculations and simulations as well. Excellent agreement was found for the mean location of these individual spots.
The instrument suite of the European Spallation Source Jackson, A.J.; Toft-Petersen, R.; Beran, P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2020, Letnik:
957, Številka:
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Journal Article
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An overview is provided of the 15 neutron beam instruments making up the initial instrument suite of the European Spallation Source (ESS), and being made available to the neutron user community. The ...ESS neutron source consists of a high-power accelerator and target station, providing a unique long-pulse time structure of slow neutrons. The design considerations behind the time structure, moderator geometry and instrument layout are presented.
The 15-instrument suite consists of two small-angle instruments, two reflectometers, an imaging beamline, two single-crystal diffractometers; one for macromolecular crystallography and one for magnetism, two powder diffractometers, and an engineering diffractometer, as well as an array of five inelastic instruments comprising two chopper spectrometers, an inverse-geometry single-crystal excitations spectrometer, an instrument for vibrational spectroscopy and a high-resolution backscattering spectrometer. The conceptual design, performance and scientific drivers of each of these instruments are described.
All of the instruments are designed to provide breakthrough new scientific capability, not currently available at existing facilities, building on the inherent strengths of the ESS long-pulse neutron source of high flux, flexible resolution and large bandwidth. Each of them is predicted to provide world-leading performance at an accelerator power of 2 MW. This technical capability translates into a very broad range of scientific capabilities. The composition of the instrument suite has been chosen to maximise the breadth and depth of the scientific impact of the early years of the ESS, and provide a solid base for completion and further expansion of the facility.
Small Angle Scattering techniques are now commonly used worldwide by scientists to characterize their samples. Collimator slit size opening is one among many parameters that the user can fine tune to ...fit his experiment in terms of the balance between intensity, resolution and transmitted beam size on the detector. Although every instrument in the world offer this possibility, surprisingly very few offer the possibility to change the beam stop size, located in front of the detector, to match with transmitted beam size. This article describes a device allowing changing beam stops remotely and reliably during an experiment, and its integration into an existing instrument.
The design and characteristics of the new very‐small‐angle neutron scattering spectrometer under construction at the Laboratoire Léon Brillouin are described. Its goal is to extend the range of ...scattering‐vector magnitudes towards 2 × 10−4 Å−1. The unique feature of this new spectrometer is a high‐resolution two‐dimensional image‐plate detector sensitive to neutrons. The wavelength selection is achieved by a double‐reflection supermirror monochromator and the collimator uses a novel multibeam design.
The response of a position-sensitive Li-glass based scintillation detector being developed for thermal-neutron detection with 6 mm position resolution has been investigated using focused beams of ...2.5MeV protons and deuterons. The beams were scanned across the detector in 0.5 mm horizontal and vertical steps perpendicular to the beams. Scintillation light was registered using an 8 × 8 pixel multi-anode photomultiplier tube. The signal amplitudes were recorded for each pixel on an event-by-event basis. Several pixels generally registered considerable signals at each beam location. To optimize planned detector operation at the European Spallation Source, the number of pixels above set thresholds was investigated, with the maximization of the single-hit efficiency over the largest possible area as the primary goal. For both beams, at a threshold of ∼50% of the mean of the full-deposition peak, ∼80% of the events were registered in a single pixel, resulting in an effective position resolution of ∼5 mm in X and Y. Lower thresholds resulted in higher pixel multiplicities. These events could also be localized with the same effective position resolution.
We present a summary description of the 8th annual international Design and Engineering of Neutron Instruments Meeting (DENIM) which was held in North Bethesda, MD, USA, September 17–19, 2019. DENIM ...VIII was organized by the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) in combination with the University of Maryland (UMD). DENIM specifically addresses the unique field of neutron instrument engineering, a subcategory of neutron scattering science. DENIM is organized by engineers for engineers who share openly about what works and what doesn’t work in the life cycle design of an instrument used to analyze materials with neutrons. DENIM is held under the patronage of the International Society of Neutron Instrument Engineers which was formed in 2017. At DENIM VIII, there were 3 keynote talks, 29 additional presentations and 13 posters (presented to the plenary in a poster slam session). Attendees toured the unique labs at NIST including the NCNR. Four parallel knowledge sharing sessions helped attendees explore mutual challenges and solutions in the areas of Instrument Installation Survey and Alignment, Electrical Grounding, Choppers and Velocity Selectors, and 3D Printing.
The response of a position-sensitive Li-glass scintillator detector to alpha-particles from a collimated Am-241 source scanned across the face of the detector has been measured. Scintillation light ...was read out by an 8 x 8 pixel multi-anode photomultiplier and the signal amplitude for each pixel has been recorded for every position on a scan. The pixel signal is strongly dependent on position and in general several pixels will register a signal (a hit) above a given threshold. The effect of this threshold on hit multiplicity is studied, with a view to optimize the single-hit efficiency of the detector.
The design and characteristics of a double‐supermirror monochromator for neutron instrumentation at the Laboratoire Léon Brillouin are described. The aim of this monochromator is to reduce the ...intense γ radiation produced by conventional velocity selectors and to avoid a direct view of the guide while keeping a comparable neutron transmission (70%). The monochromator offers a continuous choice of wavelength selection in the range 0.5–2 nm.
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