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Login Investors Careers. Physical Science. Learning Centre Asset. Complementing X-ray imaging with Neutron Radiography Neutron Radiography NR is a useful non-destructive imaging system that uses thermal energy neutrons to probe the internal sections of various materials.
Neutron tomography A useful imaging technique used more and more is computed tomography, which applies to neutron as well as X-ray imaging. Neutron imaging applications Neutron radiography and tomography 3D radiographic imaging are highly useful techniques for examining the inside of metal castings to check for voids and weakness. Generating neutrons Most neutron radiography uses thermal neutrons, which are defined as neutrons with energy of about 0. Obtaining neutron-based images Detectors for Neutron Imaging NI are those able to measure the neutron field in two dimensions perpendicular to the beam direction.
The Zyla from Andor is a camera that delivers a low noise, a large target field of view and full frames per second and faster rates for smaller regions of interest If the application also requires single photon sensitivity, then an electron-multiplying charge coupled device EMCCD detector should be selected such as the iXon Ultra with its fast 30 MHz and 26 fps readout capability. Conclusion Although up to now neutron and X-ray imaging have been used as separate entities there are instances where they have been combined in a hybrid fashion for a new dual-modal contrast imaging technique.
References Pleinert et al. A, , volume , R. Imel et al. Grosse et al. Krzemnicki, C. Berger H. Advances in neutron radiographic techniques and applications: a method for non-destructive testing, Appl Radiat Isotopes ; Felix H. In the next three chapters, I consider spectra-both high- and low-resolution--of accretion-powered millisecond X-ray pulsars, a unique and relatively new class of objects. In addition to analysis of the pulsar XTE J, I compare a broader sample of pulsars with a sample of atoll sources in order to better understand why the latter class do not contain persistently pulsating neutron stars.
In particular, I test the hypothesis that pulsations in the atoll sources are suppressed by a high-optical- depth scattering region. Using X-ray color-color diagrams to define a selection criterion based on spectral state, I analyze Rossi X-ray Timing Explorer RXTE spectra from all the sources, and use a Comptonization model to obtain measurements of their optical depths. I then discuss efforts to spatially resolve X-ray jets from the accretion-powered millisecond pulsar SAX J Each was observed by the Chandra X-ray Observatory to produce a high-spatial-resolution image.
This work was motivated in part by my analysis of XTE J, which found an apparent excess of infrared flux which could be attributed to jet emission. Next, I discuss the measured temperatures of thermonuclear X-ray bursts. The detection of line features in these bursts, and hence from the surfaces of neutron stars, has been an important goal for high-resolution X-ray spectroscopy. A measurement of the wavelengths of identified line features would yield a measurement of the neutron star's gravitational redshift, which would help constrain current models for the neutron star equation of state.
Neutron and X-ray Spectroscopy : Françoise Hippert :
Help us improve our products. Sign up to take part. A Nature Research Journal. Some cultured and natural pearls can be reliably distinguished by visual inspection and by the use of lens and microscope. However, assessing the origin of the pearls could be not straightforward since many different production techniques can now be found in the pearl market, for example in salt or freshwater environments, with or without a rigid nucleus.
This wide range of products requires the use of new effective scientific techniques.
Indeed, X-ray radiography has been used by gemologists since last century as the only safe and non-destructive way to visually inspect the interior of a pearl, and recently, also X-ray computed micro-tomography was used to better visualize the inner parts of the gems. PCI and NI results will be combined for the first time, to better visualize the pearls internal morphology, thus giving relevant indications on the pearl formation process.
Natural pearls were considered precious and rare gems for many centuries. There is an important price gap between the two kinds of pearls: cultured pearls may cost a few hundreds of dollars while the natural pearls can be sold for millions of dollars. As the culturing techniques have improved, the distinction between natural and cultured pearls has become a challenging task and still an open question for gemologists 1 , 2 , 3 , 4. Apart from obvious cases of internal structures evidenced clearly by using the traditional methods, there are cases in which better resolution and sensitivity are needed to highlight the subtle characteristics necessary for pearl identification.
The biological mechanisms of molluscs responsible for pearl creation are the same of shell secretion. All pearls are very complex biogenetic structures 5 , consisting of inorganic matrix-mediated mineralization, mainly of calcium carbonate in calcite and aragonite phases, performed by living tissues.
The calcifying matrix is a mixture of proteins, glycoproteins and polysaccharides that precisely self-assemble and control the CaCO 3 polymorph, the size, the shapes of the crystals and their orientation 6. The complexity of these structures is proved also by the fact that not all the biochemical reactions involved during the pearl genesis are understood yet. For decades, the analysis of pearls was mainly based on the X-ray radiography 7 , 8 that allows to visualize slight variations in X-ray absorption. However, this technique is often inefficient to reveal small intrinsic structure variations of pearls.
Only recently, the X-ray computed micro-tomography was used to better reconstruct the inner parts of the gems 9 , 10 , Other techniques involving X-ray laboratory sources and based on the so called phase contrast mechanism were tested 12 , 13 and compared with neutron imaging techniques 14 , Recently, an energy resolved neutron imaging study on pearls was carried out to analyse the phase composition Yet, the newest pearl culturing techniques may require a combination of multiple test methods.
PCI basically takes advantage of the phase shift that occurs when an X-ray beam passes through an object This class of techniques has been shown to lead to a superior image contrast compared to the conventional X-ray attenuation-based imaging, especially for low atomic number samples, and therefore including biological samples. On the other hand, neutrons are strongly attenuated by hydrogen and easily transmitted through metals; as a consequence NI gives complementary results respect to X-ray imaging.
In this regard, neutrons could be a suitable probe to observe the various kind of pearl structures and differentiate organic tissues from inorganic carbonate phases and, possibly, also disclose the origin of pearls in uncertain cases. In this work we chose three different pearls as a case study: a natural pearl, a bead cultured pearl and a non-bead cultured pearl. Images of the samples are displayed in Fig. From left to right the natural pearl NP, the bead saltwater pearl CP and the non-bead freshwater cultured pearl CP NP is a vintage pearl with a negligible commercial value from a private collection and it has been sewed for didactical purposes.
The sewing process could have partially modified the core appearance, but this is a secondary aspect for our work purpose. Therefore, sewed NP represents a very suitable sample to test the imaging techniques due to its well visible complex structures. On the other hand, CP is a classic example of non-bead freshwater cultured pearl: this type of gemological material is very cheap and common on the market, but in some cases the classic gemological tests are not enough to distinguish between natural and this type of cultured pearls.
Finally, CP presents typical bead and therefore is easy to identify it as cultured pearl.
- X-ray and Neutron Scattering of Water | Chemical Reviews.
- Modern Aspects of X-ray and Neutron Scattering.
- M. Butterfly.
Neutron Tomography NT is a non-destructive technique that provides the three-dimensional map of the neutron attenuation coefficient within a sample 22 , It consists in collecting a set of transmission radiographs at different angular views of the sample by rotating it, generally with small uniform increments over or degrees. The three-dimensional map of the attenuation coefficient is computed from a set of radiographs by means of mathematical reconstruction algorithms 24 , NI has unique capabilities with respect to X-ray imaging, such as the high-sensitivity to hydrogenous materials, the penetration of thick metals and the differentiation of isotopes of the same element or neighbour elements in the periodic table.
The pearls were placed in a tube-like sample holder and aluminium foil was used as spacing between the pearls and to fix a good positioning that prevents accidental motions during the scan. The resolution achieved for this setup is Open beam and dark images were taken as well in order to fulfil the flat-field correction. The data pre-processing and reconstruction were performed by means of MuhRec 30 , a software developed to support the need of users at neutron imaging beamlines. Some pre-processing steps are necessary for the right evaluation of the reconstructed images: the normalization of the projection respect to dark and open beam images, the suppression of spots caused by gamma rays hitting the CCD sensor, the computation of the rotation axis position and the ring removal by means of a filter based on combined wavelet and Fourier analysis The tomographic reconstruction was performed by means of the Filtered Back Projection FBP algorithm for a parallel beam geometry However, the reconstructed images are affected by noise that must be suppressed for a straightforward segmentation and analysis.
Hence, an Inverse Scale Space filter 32 was applied to reconstructed images by using the image processing software KipTool PCI relies on the beam phase shift occurring when X-rays pass through a sample and resulting in intensity variations recorded by a detector. Phase sensitive imaging allows obtaining higher image contrast at a lower radiation dose with respect to conventional attenuation-based imaging. Several X-ray PCI techniques have been developed in the last decades and an exhaustive description can be found in 17 , A highly spatially coherent and quasi-monochromatic X-ray beam irradiates the object, placed at a suitable distance from the detection system, and, thanks to the Fresnel diffraction, the interfaces between the different materials are strongly highlighted by the generated interference fringes.
A pole wiggler was used together with a double Si Laue crystal monochromator. The imaging detector was a PCO edge 5. The samples were placed at the distance of 2. Each tomographic scan was performed using the half-acquisition CT mode that allows almost to double the width of the field of view FOV.
Due to the vertically limited FOV and beam size, in order to scan the entire cultured pearls that are bigger than the natural pearl, two tomographic measurements were acquired at two different vertical positions. The data processing and reconstruction were performed by using SYRMEP Tomo Project STP 39 , an open-source software tool conceived for post-beamtime, allowing the users to design custom reconstruction workflows of archived data. In the pre-processing stage, the data were normalized by using the dark and flat-field images and processed by a ring suppression filter Prior the CT reconstruction, each normalized projection must be processed to extract the phase information by means of a phase retrieval procedure Finally, also in this case, the tomographic reconstruction was performed by means of the FBP algorithm for parallel beam geometry.
The 3D rendering and the registration of the X-ray data respect to neutron data were performed using the Avizo 8 software In this section we present for each pearl the results and a detailed description of the visible structures disclosed by both techniques. We recall that each NI image represents a two-dimensional map of the attenuation coefficient, so brighter pixels represent a higher neutron attenuation.
The X-ray PC images depict the refractive index decrement distribution, which is proportional to the electron density. Hence, in this case, brighter zones correspond to a higher electron density. Both reconstructed images reveal the complex inner structure composed of calcium carbonate and organic matter organized in several layers.
The aragonite phase, identified by additional micro-Raman spectroscopy analyses performed on the sewed pearl surface 43 , are clearly visible in X-ray PC image as white zones, conversely in neutron images they appear as dark grey regions. The organic matter figures as white stain in neutron images and as dark grey in X-ray PC images.
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However, the X-ray PC offers the best results in terms of resolution and detects some details that cannot be disclosed by NT. In fact, Fig. The internal portion of pearl shows concentric growth arcs, in conjunction with several layers of organic matter. The resolution of few microns gives the possibility to visualize small fissures in the inner part of the pearl Fig. Both tomographic reconstructions allow to identify not just the nacre composed of aragonite, but also aragonite structures in the core of the pearl that cannot be disclosed with neutron or X-ray radiography.
These parts of the natural pearl NP were segmented by choosing the proper grey values thresholds for the calcium carbonate phase, after the application of a denoising filter. X-ray PC a and neutron b reconstructed image corresponding to the same slice of the natural pearl NP Aragonite phases figure as white and dark grey zones in the X-ray and neutron images, respectively. Organic matter is recognized as dark grey and white zones in the X-ray and neutron images, respectively. In the neutron image an elevate concentration of organic matter has been identified, visible as white zones due to hydrogen presence.
http://fensterstudio.ru/components/wesujesun/xiqyl-como-rastrear.php On the other hand, the X-Ray PC image shows with more details the concentric growth arcs and the layers of organic matter. Three orthogonal X-ray PC slices a — c and a detail d of the slice represented in a. Small fissures and pearl structures are clearly visible, as well as in light grey a carborundum contamination due to the sewing. The identification of the beaded saltwater pearl CP is straightforwardly performed with X-ray PC and neutron radiography.
In fact, an X-ray and a neutron radiograph of the pearl CP shown in Fig.