A ZnS (Ag) scintillation detector comprises a ZnS (Ag) scintillators layer 22 which is excited by incident α-rays and emits a scintillator light, a photomultiplier tube 16 which converts the scintillator light into an electric pulse signal, and a counting rate meter 34 which counts the obtained pulse signal. The scintillator layer has a thickness which is not less than a range of α-rays from α-ray emitting nuclides (natural radioactive nuclides) to be separated, which enables energy absorption of α-rays from the α-ray emitting nuclides to be separated to entirely occur in the scintillator layer, and which enables light shielding of the scintillator light generated in the scintillator layer by the scintillator layer itself to be neglected. A pulse height discrimination circuit 32 is further provided in a preceding stage of the counting rate meter. Thereby, the effect of the natural radioactive nuclides can be reduced and the contamination control can be efficiently and smoothly performed.
展开▼
