Improvement of the minimum detectable activity of a free release monitor for small articles

Abstract

This paper presents results of the development of a small-sized free release monitor designed for the release of materials, various hand tools, equipment and instruments of nuclear enterprises and laboratories staff that weight up to 50 kg, from radiation control. To increase the registration sensitivity of controlled radionuclides, 12 scintillation units based on a 3"x3" sized NaI (Tl) crystal were used as gamma-radiation detectors. Volume of the measuring chamber of the monitor amounted to 200 L, the chosen thickness of the low-back ground shielding was 50 mm. The values of the minimum detect able activity of the designed monitor for the point sources 123I, 131I, 99mTc, 18F were better than 100 Bq with measurement time not exceeding 60 seconds.