Completion of additional Gd introduction into Super-Kamiokande


The second introduction of gadolinium (Gd) into Super-Kamiokande, which started on June 1, 2022, proceeded smoothly and was completed on July 4, as scheduled.

In order to maintain a uniform Gd concentration in the Super-Kamiokande detector tank, water with a 0.01% concentration of Gd was returned to the circulation system from the top of the tank, and water with an increased Gd concentration of 0.03% was sent to the bottom of the tank as shown in Figure 1. During the introduction process, we regularly sampled the water at various points in the tank and confirmed that the “wavefront” of increased Gd concentration was gradually and smoothly rising within the tank as shown in Figure 2.

After a few months of trial operation, a full-scale search for supernova relic neutrinos will begin.

Fig1: The 0.01% concentration of gadolinium solution was sent from the top of the SK tank to the Gd-loading system, and 0.03% concentration of gadolinium solution was fed into the bottom of the tank.
Fig2: Regular water sampling from the tank confirmed that the Gd concentration was increasing to 0.03% from the bottom to the top
Fig.3: Installation completed on schedule