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.