Neutron Spatial Distribution Measurement Using Activation Foils Fabricated by Printed Electronics Technique

Abstract

The neutron spatial distribution is an important parameter in the neutron utilization study. Therefore, the distirbution should be accurately determined before or during the experiment. Various detectors can be utilized to measure the neutron spatial distribution, including a position-sensitive He-3 detector and a CCD based on scintillation detector; however, there are difficulties in their uses for the evaluation of neutron fluence in very narrow spaces such as irradiation vials as well as for the evaluation of neutron energy. For this reason, an array-type threshold detector consisting of a combination of multiple two-dimensional (2D) foil arrays with the different elements are extensively utilized to determine the neutron field (energy, spatial distribution). The activation foils are inexpensive, also do not require detector calibration, and exclude background gamma-rays, all while enabling the reconstruction of the neutron energy information using the unfolding method. However, the activation foil method has a limitation in terms of dense arrangement and its precision while also requiring a time-consuming process in an arrangement. To address these problems, the two-dimensional arrangement of activation foils using a printed electronics technique was attempted in the present study. For the commercialization of the proposed technology in the near future, the study was conducted in five stages: manufacturing technology development for the activation foil, evaluation technique development for manufacturing quality, manufacturing quality evaluation, neutron irradiation testing and methodology verification. The first stage showed that the activation foil array was fabricated by using a dispenser and the screen printer. For the second stage, the manufacturing quality evaluation technique for the mass determination of each activation foil was developed. As the printed activation foils require non-contact mass evaluation, this study developed the mass evaluation technique based on the X-ray microscopy. In the third stage, the uniformity of the printed activation foils was evaluated by using the developed technique, verifying that the mass error of foils was within 3%. In the fourth stage, neutron irradiation experiments were performed, which demonstrated that the neutron spatial distribution can be evaluated by using the printed activation foil array. In the fifth stage, it was demonstrated that the activation foils of a three-dimensional array can measure the spatial distribution according to the neutron energy. In the present study, the spatial distribution of neutron fluence and energy at the MC-50 cyclotron facility was measured by the activation foils using the printed electronics technique. It was confirmed that the slope of the fast neutron distribution was 18.5% lower than that calculated by the Monte Carlo simulation and the ratio of thermal to the total fluence rate in the measured distribution was 40% to 70% higher than the calculated one. To correct those different, it is required to perform various measurement using printed activation foils