Target and shielding design of accelerator-driven transportable neutron source

We have started a project, which is a prototyp of a portable neutron source aiming at on-site use for diagnosing deterioration of social infrastructure, such as concrete structures, by using a first neutron imaging technique. A project is named as RANS-2, and based on experimental results obtained at RIKEN Accelerator-driven compact Neutron Source (RANS). From the compactness point of view, along with accelerator, the target station design is important. We adopted the 7Li(p,n)7Be reaction to produce neutrons and the proton energy of 2.49 MeV from an efficient neutron production point of view. In this paper, firstly we report the target neutron characteristics, such as neutron yield, and angular distribution. Secondly, shielding performances of several commercially available candidate materials, in terms of attenuation of fast neutrons in concrete, were evaluated using a Monte Carlo calculation. It is suggested that the boron-added polyethylene is the most effective material for neutron shielding. The flexibility of boron-added rubber (80 wt%, B4C) is also attractive.