Development of a Sealed Li target as an accelerator-driven neutron source for Boron neutron capture therapy at Nagoya University

Nagoya University is developing a Sealed lithium (Li) target based on a new concept for an accelerator-driven neutron source for Boron neutron capture therapy. The Sealed Li target is a thick Li target with the new concept of sealing Li with Ti foil and stopping protons within Li. The incident proton beam on the target is generated by the Proton-dynamitron (IBA) accelerator and has a maximum energy of 2.8 MeV and a current of 15 mA (heat input of 6.6 MW/m²). In this paper, a test sample made with a small amount of Li was prepared to evaluate the performance of the Sealed Li target. We called the test target. When irradiated with a heat input of 4.6 MW/m², the Ti foil on the surface of the test target was not damaged, although some Li melted and a dent with the same shape as the beam diameter was formed. Furthermore, the heat removal performance of the test target was evaluated using simulation software and the finite element method. The maximum temperature of the target surface was 144.4 °C when a heat input of 5.0 MW/m² was calculated. Assuming that the bondability between Ti foil and Li is poor, the calculation was carried out by simulating the presence of cavities at the Ti foil–Li​ interface. As a result, we suggested that the presence of than 2 mm diameter cavity at the interface between Ti foil and Li would melt the Ti foil and damage the target. In order to obtain the ideal result, it was necessary to further improve the adhesion between Ti foil and Li, but we were able to confirm the performance of the sealed Li target with a new concept.