12 research outputs found
The new very small angle neutron scattering spectrometer at Laboratoire Leon Brillouin
The design and characteristics of the new very small angle neutron scattering
spectrometer under construction at the Laboratoire Leon Brillouin is described.
Its goal is to extend the range of scattering vectors magnitudes towards
2x10{-4} /A. 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
A double supermirror monochromator for neutron instrumentation at LLB
The design and characteristics of a double supermirror monochromator for
neutron instrumentation at the Laboratoire Leon Brillouin is described. The aim
of this monochromator is to reduce the intense gamma-radiation produced by
conventional velocity selectors and to avoid a direct view of the guide while
keeping a comparable neutron transmission (higher than 70%). The monochromator
offers a continuous choice of wavelength selection in the range 0.5 to 2 nm
Evidence for Environmental Changes in the Submillimeter Dust Opacity
The submillimeter opacity of dust in the diffuse Galactic interstellar medium
(ISM) has been quantified using a pixel-by-pixel correlation of images of
continuum emission with a proxy for column density. We used three BLAST bands
at 250, 350, and 500 \mu m and one IRAS at 100 \mu m. The proxy is the
near-infrared color excess, E(J-Ks), obtained from 2MASS. Based on observations
of stars, we show how well this color excess is correlated with the total
hydrogen column density for regions of moderate extinction. The ratio of
emission to column density, the emissivity, is then known from the
correlations, as a function of frequency. The spectral distribution of this
emissivity can be fit by a modified blackbody, whence the characteristic dust
temperature T and the desired opacity \sigma_e(1200) at 1200 GHz can be
obtained. We have analyzed 14 regions near the Galactic plane toward the Vela
molecular cloud, mostly selected to avoid regions of high column density (N_H >
10^{22} cm^-2) and small enough to ensure a uniform T. We find \sigma_e(1200)
is typically 2 to 4 x 10^{-25} cm^2/H and thus about 2 to 4 times larger than
the average value in the local high Galactic latitude diffuse atomic ISM. This
is strong evidence for grain evolution. There is a range in total power per H
nucleon absorbed (re-radiated) by the dust, reflecting changes in the
interstellar radiation field and/or the dust absorption opacity. These changes
affect the equilibrium T, which is typically 15 K, colder than at high
latitudes. Our analysis extends, to higher opacity and lower T, the trend of
increasing opacity with decreasing T that was found at high latitudes. The
recognition of changes in the emission opacity raises a cautionary flag because
all column densities deduced from dust emission maps, and the masses of compact
structures within them, depend inversely on the value adopted.Comment: Original version (22 Dec 2011): 14 pages, 8 figures. Revised version
(24 February 2012) accepted for publication in the Astrophysical Journal (14
March 2012): elaborated details of analysis, extended discussion including
new Appendix; abstract, results, conclusions unchanged. 16 pages, 9 figure
Neutron imaging and tomography: Applications in food science
Neutron imaging and tomography allow observing the structure of large objects (from few to hundred centimeters) at a resolution around 100 μm. This nondestructive method is based on the detection of the transmission of a neutron beam through an object in 2D (imaging) or 3D after rotating the sample (tomography). The components of the object attenuate the neutron beam differently, depending on their composition, and produce accurate pictures of objects which give information about their structure. Neutron imaging has been used for quality control purposes in industries (aircraft, motor engineering...), but also find application from materials sciences (fuel cells, lithium batteries) through earth science (petrology, geology) to cultural heritage. More recently studies have been performed on food science topics
Neutron imaging and tomography: Applications in food science
International audienceNeutron imaging and tomography allow observing the structure of large objects (from few to hundred centimeters) at a resolution around 100 μm. This non-destructive method is based on the detection of the transmission of a neutron beam through an object in 2D (imaging) or 3D after rotating the sample (tomography). The components of the object attenuate the neutron beam differently, depending on their composition, and produce accurate pictures of objects which give information about their structure. Neutron imaging has been used for quality control purposes in industries (aircraft, motor engineering...), but also find application from materials sciences (fuel cells, lithium batteries) through earth science (petrology, geology) to cultural heritage. More recently studies have been performed on food science topics
Ultrafine Selective Metal-Complexing Nanoparticles: Synthesis by Microemulsion Copolymerization, Binding Capacity, and Ligand Accessibility
Neutron Imaging of Meat during Cooking
International audienceNeutron imaging was used to follow the impact of cooking on beef meat. During online cooking, the cartography realised on image collected shows neutron attenuation per zone. Some data points were taken on the edge to highlight higher attenuation variations because of "microscopic" shrinkage of the meat at 70 degrees C. Some others points were taken in the centre of the sample, which first showed smaller decreases at 75 degrees C and then an increase around 80 degrees C. These smaller attenuation variations are possibly linked to denaturation of connective tissue which in turn influenced meat microstructure allowing the release of entrapped water and increase the thickness of the sample
Toward a new lower limit for the minimum scattering vector on the very small angle neutron scattering spectrometer at Laboratoire Leon Brillouin
International audienceThe main characteristics of the very small angle neutron scattering spectrometer (VSANS) under construction at the Laboratoire Leon Brillouin are a multibeam pinhole collimator converging onto an image plate detector. By combining tiny collimation (diaphragms of around I or 2 mm in diameter) with the small pixel size of the detector (0.15 x 0.15 mm), very high resolution measurements can be achieved. The resolution function of the instrument contains a contribution from gravity, which is reduced by the intermediate masks of the collimator. Owing to the relatively short length of the VSANS instrument (around 14 m), this effect remains weak, in good agreement with the predictions. With a prototype multibeam collimator, an incident wavelength of 0.9 nm and the detector located at 6 m from the sample, it is possible to access q values as low as 4 x 10(-3) nm(-1) with very high q resolution. Promising preliminary experiments with high q resolution are reported, which open up new fields to the SANS technique