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Development of a Large-Field Cold Neutron Source at the University of California, Davis, McClellan Nuclear Radiation Center (UCD/ MNRC)

  • Author(s): Flocchini, R.
  • Liu, H. B.
  • Boussoufi, M.
  • et al.
Abstract

The project is to investigate, study, and develop a large-field, beryllium filtered cold neutron source for use in performing neutron radiography for a wide variety of basic research activities at the UC Davis/ McClellan Nuclear Radiation Center (MNRC). The UCD/ MNRC’s 2-MW TRIGA reactor which went online in 1990, and is the youngest research reactor in U.S. is renowned for its world-class facilities for performing thermal neutron radiography. It provides support for non-destructive inspection of materials and technology in the automotive, aerospace, and material science areas. The proposed research intends to study, design, modify, and transform one of the existing four thermal neutron radiography beams into a large-field, beryllium filtered cold neutron radiographic beam. When added to the extensive experiences in thermal neutron radiography, this additional capability will further enhance the existing thermal neutron radiography to support basic research activities in the automotive, aerospace, material, chemical, and biological sciences. It will also make investigating crucial dynamic (real-time) engineering problems such as flow restrictions across valves or two-phase flow situations feasible. The project is dedicated to advancing our existing technology of implementing neutron radiography and development of fundamental nuclear science and technology. Thermal neutron radiography is a well-known powerful tool for non-destructive inspection of materials, especially industrial materials, as a complementary technique to X-ray radiography. The capability of neutron radiography, as compared with X-ray radiography, is determined by the features of the neutron-matter interactions. X-rays interact mainly with the electron shells of the atoms, therefore the cross sections for X-rays increase with the atomic number making it very difficult to image low atomic number elements (i.e. hydrogen, carbon, etc.). In contrast, neutrons interact with atomic nuclei, so that dependence on atomic number is not observed. This major difference enables thermal neutron radiography to significantly outperform X-ray radiography in detecting elements such as H, Li, O, N, B, Cd, Gd in structural metals such as Al, Fe, Zr, Sn, W, Pb. In comparison to thermal neutrons (Eavg = 0.0253 eV), beryllium filtered cold neutrons (energies < 0.005 eV) are attenuated to an even greater extent by the elements listed above and to a lesser extent by those structural metals listed above. As a consequence, imaging contrast and sensitivity are significantly enhanced for detecting minute quantities of hydrogen in thick layers of metal. On the other hand, all existing cold neutron sources are confined to < 6 cm in diameter in the U.S., which potential applications are thus limited. Based on the existing experiences and facilities of thermal neutron radiography at the UCD/ MNRC, we investigate and study such a large-field, beryllium filtered cold neutron source to expand our understanding of cold neutron nuclear characteristics and support basic research applications in other scientific fields.

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