Patent ID: 7151262

Claim:
A radioactive gas measurement apparatus for measuring radiation of radioactive gas, comprising: a main detector and a sub-detector that are arranged at positions diametrically opposed to each other with respect to a sampling chamber, into or out of which a radioactive gas flows, and a shield for shielding a background radiation surrounding the detectors, wherein said shield defines first and second collimators, said first collimator adapted to collimate radiation emitted from a gas in the sampling chamber toward the main detector, and said second collimator adapted to collimate radiation emitted from a gas in the sampling chamber toward the sub-detector, and said shield is made of a material that does not allow penetration of a characteristic X ray within a range of energy from 70 to 90 keV inclusive; wherein the main detector is a detector made from a plate-shaped semiconductor detector having a thickness of between 2 mm and 7 mm, the sub-detector is a scintillation detector, wherein a thickness of the scintillation detector is thicker than that of the semiconductor detector, and wherein the radiation of the radioactive gas is measured by processing both signal of the plate-shaped semiconductor detector and the scintillation detector.