Improvement of geometry and size of a neutron production target for a higher intensity electron accelerator-driven pulsed neutron source

At the pulsed neutron source facility based on an electron linear accelerator at Hokkaido University, HUNS (Hokkaido University Neutron Source), high wavelength-resolution time-of-flight (TOF) neutron imaging experiments are performed using a decoupled thermal neutron moderator system. However, the neutron intensity is lower than that of a coupled moderator system due to the narrow neutron pulse. To increase the neutron intensity, we considered increasing the neutron intensity provided from a neutron production target located at the most upstream of a neutron beamline. In this study, we improved the target geometry and size to realize a neutron source with not only narrower pulse but also higher intensity. By using particle transport simulation calculations, the target-moderator-in-line geometry was proposed, thereby enhancing the coupling between target and moderator in the in-line geometry. Additionally, enlarging the target size resulted in a reduction of photons entering the neutron beamline owing to the self-shielding effect of the target. In the performance evaluation experiment, the neutron intensity successfully increased by a factor of 2.25, and the spread of the neutron pulse width was suppressed, nevertheless a significant increase in the photon flux.