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Neutronics
Published in Kenneth D. Kok, Nuclear Engineering Handbook, 2016
The fifth step of reactor analysis “burns” the reactor for a user-specified period of time to update the isotopic contents, then returns to Step 2. The reactor composition changes with time due to irradiation effects and radioactive decay. These effects must be taken into account in the design of the reactor, in fact may be the primary design consideration of the reactor itself (e.g., the high flux isotope reactor at the Oak Ridge National Laboratory).
Light Scattering by Polymer Solutions
Published in Timothy P. Lodge, Paul C. Hiemenz, Polymer Chemistry, 2020
Timothy P. Lodge, Paul C. Hiemenz
A detailed description of a SANS instrument is beyond our scope, but a generic configuration consists of a source, a wavelength selector, beam guides, sample environment, and a two-dimensional detector (see Figure 8.14). The neutrons can be created in a reactor (such as at the National Institute of Standards and Technology National Center for Neutron Research, the High Flux Isotope Reactor at Oak Ridge National Laboratory, or the Institute Laué-Langevin in Grenoble) or at a spallation source (Spallation Neutron Source at Oak Ridge or ISIS at Rutherford Laboratory, UK); we will focus on the former. The wavelength can be selected by Bragg diffraction from a crystal such as silicon, or by a velocity selector; the latter has the virtue of tunability and higher flux, but at the cost of larger wavelength spread (Δλ/λ ≈ 0.1 − 0.2). The beam guides shape the beam over a distance of several meters, but it is important to emphasize that the instrument components we take for granted in optical experiments (lenses, mirrors, fiber optics, polarizers, etc.) are much less refined for neutrons. The beam dimension at the sample is defined by an aperture, and is typically ≈ 1 cm in diameter. The area of the detector is about 1 m2, with either 64 × 64 or 128 × 128 pixels. Each neutron is detected after it collides with a 3He atom; this sets off an exothermic ionization cascade that is detected as a spatially and temporally resolved pulse of electrical current. Thus the detector records a very high fraction ε of all incident neutrons. The detector is mounted on a rail in a large evacuated chamber, and can be moved automatically from 1 − 15 m from the sample, in order to tune the accessible q range (see Problem 8.33). The largest accessible q is determined by the outermost pixels of the detector; the lowest usable q is set by the diameter of the beamstop, which prevents the unscattered beam from damaging the detector.
3D printing rises to the occasion
Published in Adedeji B. Badiru, Vhance V. Valencia, David Liu, Additive Manufacturing Handbook, 2017
Quality control is also an issue, one that is especially important in areas such as medical implants or aerospace manufacturing. In response, Duty’s group is working with ORNL neutron scientists at both the Spallation Neutron Source and the High Flux Isotope Reactor, using the unique ability of neutrons to look inside materials without damaging them.
Design Studies for the Optimization of 238Pu Production in NpO2 Targets Irradiated at the High Flux Isotope Reactor
Published in Nuclear Technology, 2020
Charles R. Daily, Joel L. McDuffee
The HFIR is a U.S. Department of Energy (DOE) user facility that was originally designed in the late 1950s and early 1960s for the sole purpose of producing transplutonium isotopes.8 Operations in support of this mission began in 1966. Today, the mission-space of the HFIR includes thermal neutron scattering experiments, numerous isotope production campaigns (including 238Pu), and materials irradiation and testing initiatives.