Dr. Alexandru Dan Stoica Profile

Dr. Alexandru Dan Stoica

Associate Scientist at Oak Ridge National Lab

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Publications (8)

Proceedings Article | 21 October 2004 Paper

Multiple-stage tapered neutron guide as a broad band focusing system

Alexandru Stoica, Xun-Li Wang, Wai-Tung Lee, James Richardson

Proceedings Volume 5536, (2004) https://doi.org/10.1117/12.560007

KEYWORDS: Monte Carlo methods, Mirrors, Reflection, Spatial resolution, Scattering, Nickel, Diffraction, X-ray optics, Beam shaping, X-rays

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Proceedings Article | 18 November 2002 Paper

Silicon-based glancing incidence reflection superposition lens

Alexandru Stoica, Xun Li Wang

Proceedings Volume 4785, (2002) https://doi.org/10.1117/12.451685

KEYWORDS: Mirrors, Semiconducting wafers, Silicon, Reflectors, Scattering, Superposition, Reflectivity, Spatial resolution, Reflection, Laser scattering

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Proceedings Article | 18 November 2002 Paper

Neutron Guinier camera

Mihai Popovici, Alexandru Stoica, David Worcester

Proceedings Volume 4785, (2002) https://doi.org/10.1117/12.451679

KEYWORDS: Semiconducting wafers, Cameras, Sensors, Silicon, Crystals, X-rays, Scattering, Collimation, Spatial resolution, Laser scattering

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The feasibility of Guinier cameras for small angle neutron scattering (SANS) is analyzed theoretically and experimentally. Small angle X-ray scattering (SAXS) is commonly measured with Guinier cameras1 that use bent perfect crystals to focus to detector beams from point sources of characteristic X-rays. Neutron Guinier cameras do not exist yet, although focusing to detector has occasionally been tried. The philosophy of current SANS pinhole instruments is to gain intensity from broad wavelength bands at tight collimation. With characteristic X-rays, intensity gains can only come from broad angular divergences. Neutron focusing instruments represent a return, at a higher level, to the philosophy of characteristic X-rays. Such a return is advocated in this paper for SANS. The resolution of Guinier cameras is defined not by the collimation (which is relaxed), but by the beam size at focus and the spatial resolution of the position sensitive detector (which should match each other). Within the recent concept of neutron imaging2 multi-wafer monochromators can provide image sizes comparable to the thickness of one wafer in the bent packet. The imaging may be non-dispersive, at broad wavelength bands, like with mirrors in conventional optics. These are the right ingredients for convergent neutron beams in Guinier cameras. The paper addresses the question whether the increased angular divergence can compensate for the reduced size of the source that is imaged into a sharp spot at detector. A neutron Guinier camera at thermal neutron energies is evaluated. It turns to be quite feasible, providing moderate resolution at high intensity with detection systems in current use for high-resolution neutron diffraction. High-resolution SANS is also possible with detection by image plates or microchannel plate systems. Tests were performed using a single wafer and a packet of bent silicon wafers in both Bragg and Laue (transmission) geometry in non-dispersive imaging arrangements. Experiments have confirmed expectations. SANS data obtained in neutron Guinier camera conditions on samples of collagen and lipids are presented.

Proceedings Article | 8 November 2001 Paper

Multiwafer focusing neutron monochromators and applications

Mihai Popovici, Alexandru Stoica, Camden Hubbard, Stephen Spooner, Henry Prask, Thomas Gnaeupel-Herold, Peter Gehring, Ross Erwin

Proceedings Volume 4509, (2001) https://doi.org/10.1117/12.448073

KEYWORDS: Semiconducting wafers, Silicon, Monochromators, Reflectivity, Crystals, Sensors, Atrial fibrillation, Diffraction, Laser crystals, Scattering

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Proceedings Article | 8 November 2001 Paper

Neutron imaging with Bragg mirrors

Alexandru Stoica, Xun-Li Wang, Mihai Popovici, Camden Hubbard

Proceedings Volume 4509, (2001) https://doi.org/10.1117/12.448060

KEYWORDS: Crystals, Semiconducting wafers, Diffraction, Mirrors, Scattering, Spatial resolution, Silicon, Reflection, Laser scattering, Sensors

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Proceedings Article | 8 November 2001 Paper

Depth-graded multilayers as neutron Doppler converters at pulsed neutron source

Alexandru Stoica, Morris Crow, Jack Robertson

Proceedings Volume 4509, (2001) https://doi.org/10.1117/12.448061

KEYWORDS: Doppler effect, Crystals, Reflectors, Diffraction, Scattering, Reflectivity, Nickel, Metals, Control systems, Solid state physics

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Proceedings Article | 23 November 1999 Paper

Curved-crystal three-axis neutron spectrometry with position-sensitive detection

Mihai Popovici, Alexandru Stoica, William Yelon, Ronald Berliner

Proceedings Volume 3767, (1999) https://doi.org/10.1117/12.371130

KEYWORDS: Semiconducting wafers, Monochromators, Crystals, Energy transfer, Spatial resolution, Sensors, Scattering, Silicon, Spectroscopy, Spectrometers

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Proceedings Article | 23 November 1999 Paper

Matching bent crystals to high-brilliance sources

Mihai Popovici, Alexandru Stoica

Proceedings Volume 3767, (1999) https://doi.org/10.1117/12.371138

KEYWORDS: Crystals, Laser crystals, Reflectivity, Monochromators, Absorption, Diffraction, Silicon, Scattering, Reflection, Synchrotron radiation

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Showing 5 of 8 publications

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