PURPOSE: To detect the α rays radiated from adsorbed U, detect the gaseous UF6 in gases effectively and make reuse possible by covering the surface of a scintillator for detecting α radiations with an aluminum foil, and disposing an adsorbent for gaseous UF6 on the foil.

CONSTITUTION: A ZnS scintillator is coated on the surface of a light transmittable material, for example, a glass rod 21, and an aluminum foil is placed for surface protection. The light emitted by the ZnS scintillator is transmitted by optical guides 23 to a photoelectric multiplier 8. A prescribed number of the rods 21 are arranged in a detector cylinder 26 packed with NaF powder or granules. In order to eliminate the influence of the accumulation in NaF owing to a slight amt. of leaking gaseous UF6, NaF24 is packed in the front part of the detection surface. A filter 25 is provided to prevent scattering of the NaF and a heater 4 is provided for desorption purpose. Thereby, the leakage of the gaseous UF6 at the amt. larger than the permissible amt. to the discharge port part of gaseous UF6 handling facilities is detected.