Report of the Technical Meeting on Advances in Neutron Scattering and Imaging at Low and Medium Flux Accelerator- and Research Reactor-based Neutron Sources

Neutrons are used in scientific and technological research and development (R&D) in a very broad range of applications with significant contributions to education and training [1]. Indeed, neutrons have an array of unique properties that makes them well suited to the study of various phenomena in matter and components: neutrons are electrically neutral; they interact directly with the atomic nuclei; they are non-destructive and can penetrate deep into matter; they possess magnetic moments; and they have both wave and particle characteristics. These properties are particularly well aligned to provide efficient probes relevant to many scientific and societal challenges, including those in energy, industry, agriculture, safety and security, communications, and computing technologies, as well as the environment and healthcare. Neutron imaging (also known as neutron radiography and tomography) is a non-destructive technique that allows visualization and analysis of the inner structure of materials resolving micrometre structures in bulk samples. Neutrons exhibit a high attenuation coefficient for some light nuclei (e.g., hydrogen, boron, lithium, carbon) while penetrating through many heavier materials, such as aluminum, silicon, tantalum, and lead. Further developments extend neutron imaging beyond conventional neutron attenuation process including energy-selective imaging, interferometric imaging with phase gratings, and polarized-neutron imaging. The key properties of the slow (thermal) neutrons such as their wavelength (in the order of the inter-atomic distances) and energy (comparable to the energy of the bonding and thermal motion of the atoms) allow to study the structure and dynamics of matter that span spatial (atomic to mesoscale) and temporal (seconds to femtoseconds) scales applying neutron scattering methods. Neutron scattering is a powerful and versatile method for studying variety of phenomena encompassing many different experimental techniques to study the structure and dynamics of materials on the nanometer scale. Traditionally, for many decades research reactors were the main sources of neutrons and ionising radiation for research and other purposes. To date, some 226 research reactors in 54 countries continue to operate [2]. Of these, 45 report activity in neutron scattering, and 69 report activity in neutron imaging. In the last few decades, accelerator-based neutron sources [3] have emerged along with research reactors for neutron beam research. Depending on underlying technologies, both accelerator-based- and research reactor- neutron sources generate neutrons with wide range of intensities offering broad array of applications. The global landscape of neutron sources is constantly evolving with some facilities reaching end of their lifecycle and development of new advanced technologies and instrumentations. In addition to the IAEA's support to research reactor sustainable and safe operation as well as effective utilization, the Agency also supports new and complementary technology, namely Compact Accelerator based Neutron Sources (CANS) [4]. The state-of-the-art developments in this field provide neutron sources with intensities comparable to those of the low to medium neutron flux research reactors that are versatile, flexible, and very attractive when it comes to capital and operational costs. Neutron-based techniques play a significant role in socioeconomic development leading to a justified and ever-growing demand of neutron beam resources. That calls for cooperation and effective utilization of available resources. New methods and instrumentation have been developed that enable applying neutron imaging and scattering techniques at low and medium flux accelerator- and research reactor-based neutron sources and support to cutting-edge research and applications carried out at high flux neutron facilities. The International Atomic Energy Agency (IAEA) periodically reviews and reports the state of the art in the development of the neutron sources based on lower-energy accelerator technologies [4]. Up to date, technical information on neutron scattering techniques, instrumentation for neutron scattering, and main applications are provided in IAEA-TECDOC-1961 [5]. IAEA-TECDOC-1604 reports the results of the findings of a Coordinated Research Project on "Development of Improved Sources and Imaging Systems for Neutron Radiography" completed in 2006. In the intervening years, there has been signif-icant technical and methodological development in these subject areas. During a Technical Meeting, organizations that engage in similar activities presented their experiences, challenges, and best practices in designing and using neutron imaging and neutron scattering techniques with low or medium flux research reactor and accelerator-based neutron sources. This allowed for the exchange of information on research reactor and accelerator-based facilities, as well as relevant neutron beam instrumentation and techniques. The IAEA acknowledges the valuable contribution and support of the international experts who con-tributed to the drafting and review of this report, particularly J. Dawidowski (Argentina), F. Fernandez-Alonso (Spain), B. Gaulin (Canada), N. Kardjilov (Germany), Y. Otake (Japan), A. Venter (South Af-rica), Z.-S. Yamani (Canada). The IAEA Scientific Secretary of this meeting and follow up activities was V. Semkova of the Physics Section, Division of Physical and Chemical Sciences (NAPC).