First neutron imaging experiments at the CROCUS zero-power reactor

The steady decline of neutron imaging (NI) facilities, exacerbated by the closure of several research reactors such as Orphée (LLB, France) and BER (HZB, Germany), has increased the importance of leveraging existing reactors for NI applications. Zero-power research reactors offer a low-cost and flexible platform for student training, materials research and development, and proof-of-principle studies that can support larger neutron facilities. Previously, no dedicated NI beamline was available at the EPFL zero-power reactor CROCUS. In this work, we demonstrate neutron imaging at the CROCUS reactor for the first time. To adapt the reactor, an air-filled aluminum channel was inserted into the water reflector to enhance neutron leakage, supplemented by aluminum flight tubes to minimize transport losses. Gold foil irradiations were performed for neutron flux measurements, and a 3 He position-sensitive detector was used to map the 2D flux distribution. The neutron energy spectrum at the imaging position was subsequently calculated. A NI detector, comprising a scintillator screen coupled to a CCD camera, was installed to conduct the first imaging experiments at CROCUS. These experiments confirmed the feasibility of neutron imaging at CROCUS by capturing neutron images of a Bon religious statuette, flowers, a pacemaker and a battery, several copper and polyethylene samples, a dynamic sequence of images showing water uptake in concrete. These results provide a foundation for establishing a permanent NI facility at EPFL to complement existing regional infrastructure.