Status and Prospect of SK-Gd Project
In 2020, a new phase of Super-Kamiokande experiment, SK-Gd, was started by loading gadolinium into the pure water. This led to a high neutron detection efficiency, which allows us to distinguish different neutrino reactions, enhance signals and remove backgrounds more efficiently. In the summer of 2022, an update of SK-Gd was done by adding additional Gd, and thus totally 39 tonnes of gadolinium sulfate octahydrate has been introduced in the water. The Gd concentration was estimated as 0.0332±0.0002% based on the dissolved weight of gadolinium sulfate octahydrate powder. It is consistent with the result of the direct sampling from the detector as 334 ± 4 ppm. The spallation neutron measurement and AmBe calibration confirms the shorter capture time constant and higher capture event rate due to the second loading. Therefore, we achieved 1.5 times higher than that of the first loaded phase as expected.
