ADVANCED MATERIALS & PROCESSES | NOVEMBER/DECEMBER 2023 18 There is a broad range of nondestructive characterization techniques available to study structural, chemical, and behavioral properties of materials. Among the most popular techniques are x-ray or neutron radiography and computed tomography[1-7], x-ray or neutron diffraction[8-10], small angle x-ray or neutron scattering[11], acoustic emission[12], scanning electron microscopy[13], transmission electron microscopy[14], optical spectroscopy[15], and Raman spectroscopy[16]. Recently, a novel nondestructive capability called wavelength-dependent or hyperspectral imaging has emerged in the field of neutron radiography and computed tomography. Unlike reactor-based neutron imaging, this novel capability utilizes the ability to enhance contrast by discriminating the neutron wavelengths produced by the Spallation Neutron Source (SNS) of the Oak Ridge National Laboratory (ORNL). A dedicated facility named VENUS is currently being built to provide such unique characterization capabilities for academia, industry, and other national laboratories. This feature article describes the THE VENUS IMAGING BEAMLINE AT THE OAK RIDGE NATIONAL LABORATORY SPALLATION NEUTRON SOURCE With the VENUS beamline, hyperspectral neutron radiography measures crystalline properties (phases, lattice spacing) and elemental/isotopic content in materials. Hassina Z. Bilheux, R. Aaron Hanks, Jean-Christophe Bilheux, Harley Skorpenske, Mary-Ellen Donnelly, Jamie Molaison, and Amy Byrd Oak Ridge National Laboratory, Tennessee neutrons have energies above 1 eV (or wavelengths shorter than 0.28 Å). These energies are orders of magnitude less than needed for x-ray imaging. The VENUS beamline is designed to provide cold, thermal, and epithermal neutrons (see next section for more details). THE VENUS INSTRUMENT AND ITS CAPABILITIES The SNS is a pulsed neutron source that provides the ability to time-stamp neutrons based on their time of arrival, t, at the detector since the travel distance is known (and fixed). At VENUS, the detectors are located L = 25 m from the source. Presuming that a neutron travels the distance L in t = 7 ms, and knowing ν = L/t = 3.57 × 103 m·s-1, the neutron wavelength or energy can be calculated using Eqs. 1 and 2: λ = 1.11 Å and E = 0.06 eV. Hence, a neutron traveling 25 m in 7 ms has a wavelength of 1.11 Å or an energy of 0.06 eV. This method of determining the neutron characteristic is called the time-of-flight (TOF) technique. Similarly, a neutron that travels L in ~100 µs will VENUS capabilities for materials science and engineering, provides a quick overview of the modes of access of the facility, and illustrates the non- destructive measurements and interpretation of results. INTRODUCTION Neutrons interact with the nucleus of an atom and thus provide a complementary contrast to x-rays. The neutron wavelength, λ (in nm), is given by where h is Planck’s constant (h = 6.62 × 10-34 J·s), mn is the mass of the neutron (mn= 1.67 × 10-27 kg), and ν is the neutron velocity in m·s-1. For thermal and cold neutrons, the neutron wavelength is often the preferred characteristic designation used for neutrons. For more energetic neutrons (epithermal neutrons), the neutron energy, E, is preferably used and is given by In practice, thermal and cold neutrons have wavelengths ranging from approximately 1 to 10 Å, while epithermal
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