The KAMIOKANDE-II water Cherenkov detector for the measurements of nucleon decay and/or solar neutrino has been operating in the underground laboratory at a depth of 2, 700m. w. e. (meter water equivalent) in Kamioka mine of Gifu Prefecture. Concentrations of 238U, 232Th, 226Ra and 222Rn as the major background sources have been measured for various kinds of rocks, mine water, mine air and high purity water used as a detector during the period from August 1986 to December 1987. The concentration levels of these radionuclides and their seasonal variration have become clear. Some of these results have provided useful informations for decreasing the background level of water Cherenkov detector.
Radioactive aerosol exposure system for small rodents was developed, and its basic characteristics were investigated from the viewpoint of aerosol engineering on inhalation toxicology. The system has three nebulizers which liquid is feeded with syringe pump. Aerosol concentration within the exposure chamber is controlled by changing the speed of liquid feeding, and it is automatically maintained by switching one of nebulizers on the base of aerosol monitoring data from a high sensitivity photometer. Correspondingly, the air pressure and the air flow rate are controlled for keeping constant exposure. For acute exposure, animals are hold in specially designed containers, and only their noses are exposed. During exposure, the container also works as whole-body plethysmograph box and is enable us to measure animal's respiratory function.