Calibration of NaI(Tl) spectrometer for radiocesium volume-samples. Some results from Transylvania region

A four-channel NP-424 type gamma analyzer coupled with a large NaI(Tl) scin tillator was calibrated using a Cs-137 point source. The volume-samples wer e plexiglas cylindrical boxes (D = 76mm, H = 40mm) directly placed on the N aI(T1) detector. Measurements for 64 indoor positions at full-662 keV-peak were made. Sample selfabsorbtion was determined considering a linear attenu ation for gamma rays and measuring the absorption factor for maximum thickn ess of the volume sample (h(0) = 40mm). The obtained results for two types of environmental samples (soil and milk-powder) are compared with the data acquired from other Romanian laboratories, in the frame of the Environmenta l Radioactivity Action (ERA) which standardized such types of measurements. The same samples were measured with a calibrated GeLi detector (INAN - Lou vain la Neuve) and the results were in good agreement with our measurements . Using this NaI(TI) calibrated spectrometer some radiocesium deposits (56 localities) from Transylvanian region were measured. The results show that a large deposit exists in the direction NE-SW in connection with the radioa ctive cloud passing. For Alba region were measured more than 40 kBq/m(2) of cesium deposit.