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BT-6 Thermal Neutron Radiography and Tomography

BT-6 Thermal Neutron Radiography and Tomography. Build a high intensity neutron beam line that is dedicated to imaging. Neutron fluence rate should be 10 7 cm -2 sec -1 . Beam should be uniform so that it can be properly digitized within the dynamic range of the imaging system.

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BT-6 Thermal Neutron Radiography and Tomography

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  1. BT-6 Thermal Neutron Radiography and Tomography Build a high intensity neutron beam line that is dedicated to imaging. Neutron fluence rate should be 107 cm-2 sec-1. Beam should be uniform so that it can be properly digitized within the dynamic range of the imaging system. Dynamic range is typically 14 bit to 16 bit. Noise: Neutron shot noise is not so important. Photon shot noise is important Electronic digitization noise is important but can be subtracted off Most serious noise is that of thermal noise or dark current ’s and fast neutrons can overwhelm pixels and can destroy the CCD Ideal neutron source is a cold source; however, no positions are open. BT-6 good points: Brilliant source Large beam Up to 8 meters possible between source (source means aperture) and sample Area will be unused for several years

  2. Geometric sharpness Neutron images are essentially shadow images of the neutron beam due to attenuation of the neutrons that pass through an object. large uniform areas of illumination are produced by placing a sample a long distance away from a neutron point source. Point source is approximated by a circular aperture with a small diameter. Geometric sharpness is defined as the ratio of the distance from aperture to sample, L, to the diameter of the aperture, d, as shown in Figure 1. A greater ratio, L/d, or geometric sharpness results in higher resolution. Point source defined by pinhole aperture Image or Neutron shadow region rotated to be viewable Neutrons from a divergent source Neutron dark mask (Cd for example) L Un-sharp edges due to large aperture d

  3. Design Issues Need a good filter for ’s and fast neutrons 10 cm of uncooled bismuth seems to be a good choice. Shielding should remove as much of the penumbra region as possible early on.

  4. Main Entry: um·bra Pronunciation: '&m-br& Function: noun Inflected Form(s): plural umbras or um·brae /-(")brE, -"brI/ Etymology: Latin Date: 1638 1 : a shaded area 2 a : a conical shadow excluding all light from a given source; specifically : the conical part of the shadow of a celestial body excluding all light from the primary source b : the central dark part of a sunspot - um·bral /-br&l/ adjective Main Entry: pen·um·bra Pronunciation: p&-'n&m-br& Function: noun Inflected Form(s): plural pen·um·brae /-(")brE, -"brI/; or -bras Etymology: New Latin, from Latin paene almost + umbra shadow -- more at UMBRAGE Date: 1666 1 a : a space of partial illumination (as in an eclipse) between the perfect shadow on all sides and the full light b : a shaded region surrounding the dark central portion of a sunspot 2 : a surrounding or adjoining region in which something exists in a lesser degree : FRINGE 3 : a body of rights held to be guaranteed by implication in a civil constitution - pen·um·bral /-br&l/ adjective

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