ADVANCED MATERIALS & PROCESSES | NOVEMBER/DECEMBER 2023 19 Fig. 1 – The VENUS beamline layout showing the VENUS shutter, front-end optics, cave, radiological materials area (RMA) and control hutch. The VENUS servers are placed behind the hutch. Neutrons are coming from the left. have a wavelength λ ~1.58 × 10-2 Å and an energy of E ~326 eV. The interaction of the neutron with a material (i.e., the contrast of a neutron radiograph) is sensitive to its incident wavelength or energy, thus the importance to choose/ determine the neutron characteristics. Neutron imaging detector technology was developed over the past 20+ years to be able to time-stamp neutrons with an accuracy on the order of ~100 ns. This enables the ability to perform TOF imaging experiments at pulsed sources instruments such as the SNS VENUS beamline. The VENUS construction project started in 2018 and will be completed in 2024. As shown in Fig. 1, VENUS is divided into three main areas: the front-end optics section, the VENUS cave, and the control hutch/radiological materials area. The front-end area incorporates the VENUS beam defining optical components such as the variable aperture system, the choppers (used to ensure there is no frame overlap between pulses of neutrons, and to reduce overall background in the cave), the collimators, the cadmium (Cd) filter, and the evacuated flight tubes. During routine operations, the frontend is covered with concrete and is consequently inaccessible. The instrument is built with flexibility in mind; hence the experimental area called the VENUS “cave” is large (approximately 740 sq. ft or 68.7 m2 of floor space) to accommodate large samples and their environments. The beam is at a height of 7.1 ft (or 2.16 m). There is a 1 m3 space available on the sample platform, which allows the ability to scan large samples, with a vertical scanning capability is 27.6-in. (or 70.1 cm). The 25-m source-to-detector distance is chosen based on the compromise between neutron wavelength resolution and beam intensity. Since neutrons in each pulse have different energies (i.e., velocities), they arrive at the detector at different times. Longer flight paths Fig. 2 – Schematic of the VENUS cave showing the detector suite and rail system, the platform, He-filled flight tubes. The 2-ton crane is partially visible. Neutrons are coming from the right.
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