About XMASS Detector
The XMASS detector is located at the Kamioka Observatory of the Institute for Cosmic Ray Research, the University of Tokyo, Japan. It is in the Kamioka mine 1000 m underneath the top of Mt. Ikenoyama (i.e. 2700 m water equivalent underground).
The XMASS detecotor consists of the liquid xenon detecor about 1m in diameter and the water shield tank 10m in height and diameter. The liquid xenon detector consists of 642 photomultiplier tubes surrounding the 800kg liquid xenon, and the detecor is installed inside the vacuum chamber. The liquid xenon is kept in a temperature of -100 degrees. The liquid xenon emits scintillation lights if a dark matter particle recoils a xenon nucleus. The photomultiplier tubes (PMTs) surrounding the liquid xenon target detect the emitted scintillation photons.
The water shield tank plays a role to reduce the radioactive backgroud.