Conceptual design and optimization of a plastic scintillator array for 2D tomography using a compact D–D fast neutron generator Robert Adams a,n , Robert Zboray b , Marco Cortesi a,b , Horst-Michael Prasser a,b a Swiss Federal Institute of Technology, Department of Mechanical and Process Engineering, Sonneggstrasse 3, 8092 Zürich, Switzerland b Paul Scherrer Institut, Nuclear Energy and Safety Research Department, 5232 Villigen PSI, Switzerland HIGHLIGHTS  Conceptual design and optimization of a 2D fast neutron tomography system were performed.  Monte Carlo simulations were used to estimate 1.5 mm resolution and negligible scattering effects.  Geometry-based deterministic model was developed and used to verify the Monte Carlo results. article info Article history: Received 30 July 2013 Received in revised form 20 December 2013 Accepted 8 January 2014 Available online 18 January 2014 Keywords: Fast neutron tomography D–D neutron generator Plastic scintillator Fast neutron detector abstract A conceptual design optimization of a fast neutron tomography system was performed. The system is based on a compact deuterium–deuterium fast neutron generator and an arc-shaped array of individual neutron detectors. The array functions as a position sensitive one-dimensional detector allowing tomographic reconstruction of a two-dimensional cross section of an object up to 10 cm across. Each individual detector is to be optically isolated and consists of a plastic scintillator and a Silicon Photomultiplier for measuring light produced by recoil protons. A deterministic geometry-based model and a series of Monte Carlo simulations were used to optimize the design geometry parameters affecting the reconstructed image resolution. From this, it is expected that with an array of 100 detectors a reconstructed image resolution of 1.5 mm can be obtained. Other simulations were performed in order to optimize the scintillator depth (length along the neutron path) such that the best ratio of direct to scattered neutron counts is achieved. This resulted in a depth of 6–8 cm and an expected detection efficiency of 33–37%. Based on current operational capabilities of a prototype neutron generator being developed at the Paul Scherrer Institute, planned implementation of this detector array design should allow reconstructed tomograms to be obtained with exposure times on the order of a few hours. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction Neutron transmission imaging is a valuable tool that has been used for non-destructive testing in a variety of applications (Lehmann et al., 2004). Thermal and cold neutron attenuation has the advantage of strong isotopic dependence, including high sensitivity to hydrogen compared to many metals such as steel. Neutrons also generally have high interaction cross-sections in this energy range, meaning they are easily detected and a very good image resolution (often tens of μm) can be obtained. When a hydrogenous material is of interest, thermal or cold neutrons are often preferred over other transmission tomography techniques. However, for larger objects with a high hydrogen content, thermal and cold neutron beams can be so highly attenuated that beam starvation makes imaging difficult or impossible. For example, in Perfect et al. (2013) a water thickness of 1 cm was shown to severely attenuate both a cold and thermal neutron beam, likely making it unusable. For larger hydrogenous objects, X-ray and gamma transmission imaging can be very useful in many cases. However, attenuation of photons in this energy range increases with density and atomic number, meaning that if a significant amount of dense high-Z material (e.g., steel) is present along with some hydrogenous material, contrast in the latter will be very poor. In this case, fast neutrons are preferred because they are both highly penetrating and not attenuated dramatically by any one type of material. The tomography system outlined in this study is mainly aimed at this particular situation. Fast neutron imaging is most commonly performed using a plastic scintillator screen in which neutrons elastically scatter with hydrogen. The recoil proton induces scintillation light which is then collected by Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/apradiso Applied Radiation and Isotopes 0969-8043/$ - see front matter & 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apradiso.2014.01.001 n Corresponding author. Tel.: þ41 44 632 49 01. E-mail address: adams@lke.mavt.ethz.ch (R. Adams). Applied Radiation and Isotopes 86 (2014) 63–70