Amar Sinha

Laboratory-based X-ray phase-contrast imaging technique for material and medical science applications

In-line X-ray phase-contrast imaging technique is an emerging method for the study of materials such as carbon fibers, carbon composite materials, polymers, etc. Similarly this technique is also well suited for the imaging of soft materials such as tissues, distinguishing between tumor and normal tissue. These represent the class of materials for which X-ray attenuation cross-section is very small. Thus this method promises a far better contrast for low X-ray absorbing substances than the conventional radiography method. We have set up an experimental facility using a combination of X-ray CCD detector and a microfocus X-ray source. This facility is dedicated to micro-imaging experiments such as microtomography and high-resolution phase-contrast experiments. In this paper, the results of X-ray phase-contrast imaging experiments are described.

Laser induced shock pressure multiplication in multi layer thin foil targets

Theimpedancemismatchtechnique has been used for shock pressure amplification in two- and three-layer thin planar foil targets. Numerical simulation results using one-dimensional radiation hydrocode MULTI in two-layer targets consisting of Al–Au and Al–Cu and three-layer target consisting of plastic–Al–Au and foam–Al–Au, respectively, are presented. These results show a pressure enhancement up to 25 and 29 Mbar for plastic–Al–Au and foam– Al–Au targets, respectively, from an initial pressure of 7 Mbar in the reference material using laser intensity of 5 × 10 13 Wc m −2 at 1.064 µm. This enhancement is more as compared with 18 and 22 Mbar found in plastic–Au and foam–Au two-layer targets, respectively. Results of laser driven shock wave experiments for equation of state (EOS) studies of Au and Cu in two-layer target are also presented. A Nd : YAG laser chain (2 J, 1.06 µm wavelength, 200 ps pulse FWHM) is used for generating shocks in the planar Al foils and Al–Au (or Al–Cu) layered targets. The EOS of Au and Cu in the pressure range of 9–14 Mbar obtained shows remarkable agreement with the simulation results and with experimental data of other laboratories and SESAME data.

Design, development and first experiments on the X‐ray imaging beamline at Indus‐2 synchrotron source RRCAT, India

A full-field hard X-ray imaging beamline (BL-4) was designed, developed, installed and commissioned recently at the Indus-2 synchrotron radiation source at RRCAT, Indore, India. The bending-magnet beamline is operated in monochromatic and white beam mode. A variety of imaging techniques are implemented such as high-resolution radiography, propagation- and analyzer-based phase contrast imaging, real-time imaging, absorption and phase contrast tomography etc. First experiments on propagation-based phase contrast imaging and micro-tomography are reported.

Characterization of pyrocarbon coated materials using laboratory based x-ray phase contrast imaging technique

In-line x-ray phase contrast is an emerging x-ray imaging technique that promises to improve the contrast in x-ray imaging process. This technique is most suited for x-ray imaging of soft materials, low atomic number elements such as carbon composite fibers, very thin coatings, etc. We have used this new emerging technique for visualization and characterization of the pyrocarbon coated materials using a combination of microfocus x-ray source and x-ray charge coupled device detector. These studies are important for characterization of coating and optimization of various process parameters during deposition. These experiments will help us to exploit the potential of this technique for studies in other areas of material science such as characterization of carbon fibered structures and detection of cracks and flaws in materials. The characterization of the imaging system and optimization of some process parameters for carbon deposition are also described in detail.

Development and characterization of a neutron tomography system based on image intensifier/CCD system

A neutron tomography system has been developed using a low cost electronic imaging system which uses commercially available Image intensifier, CCD, Frame grabber. This setup has been used for a series of experiments on neutron tomography at the 400 kW swimming pool type reactor APSARA which has a neutron flux of 10 6 n/cm 2 /s at L/Da 90. The main feature of this tomography system is integrated computer controlled imaging and stepper motor control system with online data acquisition, analysis and display of images for each projection angle. The density profile of the projection images and ray sum calculation can be carried out in oCine or online manner at any slice and a series of reconstructed image for any slice can be obtained. An algorithm for reconstruction using Convolution Back Projection (CBP) technique has been developed and implemented on a Pentium system. The imaging system is modular in design. The reconstructed image has shown good quality and holes of less than 0.6 mm filled with wax can be revealed in a 60 mm aluminum matrix or 1 mm holes in 40 mm solid brass matrix have been resolved. ” 1998 Elsevier Science B.V. All rights reserved.

Accelerator-Driven Systems for Thorium Utilization in India

Research on accelerator-driven systems (ADSs) is being carried out around the world with the objectives of waste transmutation and power production. Over the last few years, the Bhabha Atomic Research Centre (BARC) has been pursuing research in the area of ADS with the primary objective of thorium utilization. ADSs can play an important role in augmenting India’s efforts for the development of nuclear power by way of the three-stage program utilizing indigenous resources. In this article, the research and development efforts in this area at BARC are outlined along with some schemes being studied for thorium utilization in ADSs.

Enhancement of laser induced shock pressure in multilayer solid targets

The impedance mismatch technique was used for shock pressure amplification in two layered planar foil targets. Numerical simulation results using one-dimensional (1D) radiation hydrocode MULTI in two layer target consisting of polyethylene (CH 2 ) n -aluminium (Al) and polyethylene (CH 2 ) n -gold (Au), show a pressure enhancement of 12 and 18 Mbar, respectively (or a pressure jump of 1.64 and 2.54, respectively), from initial pressure of 7 Mbar in the reference material (polyethylene) using laser intensity of 5 × 10 13 Watts/cm 2 at 1.064 μm. The simulation data was also corroborated by experiments in our laboratory. Results of laser driven shock wave experiments for pressure enhancement studies in CH 2 -Al and CH 2 -Au targets are also presented. A Nd:YAG laser chain (2 J, 1.064 μm wavelength, 200 ps pulse duration FWHM) is used for generating shocks in the planar CH 2 foils of thickness varying from 4 to10 μm, and in two layered CH 2 -Al (or CH 2 -Au) targets with 8 μm CH 2 and 1.5 μm Al or Au .

High sensitivity neutron imaging system for neutron radiography with a small neutron source

Abstract Although neutron radiography is a very useful NDT technique. its widespread use has been limited due to the lack of a mobile neutron radiography system. One of the major requirements in designing such a system is the development of a low fluence neutron imaging technique. In recent years several groups in France, Japan and the USA have been working on such an imaging system. We report in this paper the development of such a neutron imaging system based on a Li6F-ZnS scintillator screen using a pair of image intensifier tubes and a charge coupled device. This detector system has been employed to study the feasibility of neutron radiography using low neutron fluences. The main feature of this imaging system is its ability to detect individual neutron scintillation events with a ligh degree of spatial resolution. Details of this imaging system and the preliminary results obtained using a Pu-Be neutron source of strength ≈ 2 × 107 n/s are reported in this paper.

Quantitative studies of pyrocarbon-coated materials using synchrotron radiation.

Phase-contrast imaging provides enhanced image contrast and is important for non-destructive evaluation of structural materials. In this paper, experimental results on in-line phase-contrast imaging using a synchrotron source (ELETTRA, Italy) for objects required in material science applications are discussed. Experiments have been carried out on two types of samples, pyrocarbon-coated zirconia and pyrocarbon-coated alumina microspheres. These have applications in both reactor and industrial fields. The phase-contrast imaging technique is found to be very useful in visualizing and determining the coating thickness of pyrocarbon on zirconia and alumina microspheres. The experiments were carried out at X-ray energies of 16, 18 and 20 keV and different object-to-detector distances. The results describe the contrast values and signal-to-noise ratio for both samples. A comprehensive study was carried out to determine the thickness of the pyrocarbon coating on zirconia and alumina microspheres of diameter 500 microm. The advantages of phase-contrast images are discussed in terms of contrast and resolution, and a comparison is made with absorption images. The results show considerable improvement in contrast with phase-contrast imaging as compared with absorption radiography.

Development of three dimensional neutron tomography system and its applications

Though two dimensional (2D) neutron tomography has been used for a number of years for various industrial applications, its combination with volume visualization technique, which gives a three dimensional (3D) tomography image, has not received much attention. In order to exploit this powerful technique in the field of neutron imaging and highlight its potential applications, a 3D neutron computed tomography system has been developed for the visualization of the interior structure of the objects in their actual relative positions and orientations. The method involves first obtaining 2D neutron tomography images and then combining these images into a 3D volume data. Volume rendering techniques are used for visualization of such volume data. Industrial application of this technique in opening up an object layer by layer or cutting it at any particular angle without physical disassembly of the object is demonstrated with the help of some especially fabricated samples. Use of such a technique can overcome man...