Mechanisms of false counting in monitoring plutonium contaminations

In plutonium facilities, false counting have been experienced frequently in monitoring plutonium contaminations on clothes, gloves, vinyl sheets and arches of shoes. Electric fields, alpha contaminations and Rn concentrations were measured in the rooms of the facilities, and the conditions and the mechanisms of the false countings were studied through the measurements. It was found that the false countings are caused by the negative electrification of the surface of the objects and/or high Rn concentrations in the room air due to inflow of underground air. (author)