Optimized Activity Concentration Monitoring System for Ventilation Duct at Positron Emitters Production Center

90Sr - 90Y is one of the main sources of internal exposure, and the common method used to estimate its uptake is by measuring urine samples. Based on international safety standards the derived reference level for 90Sr-90Y is 2.2 Bq/L. Since the MDA (Minimum Detectable Activity) for direct urine measurement is higher than this level, special treatment of the urine sample must be employed. It mostly includes steps of concentration, chemical treatment, and preparation for counting. The disadvantages of the common methods are elaborate work, use of expensive materials and possible limited accuracy due to usually direct beta counting. The possible contribution of 60Co, fission products as 137Cs, or the natural 40K in urine, may also be significant. Beta particles with energy in excess of 263 keV produce Cherenkov photons in aqueous solutions, which can be detected and quantified. Cherenkov radiation measurements can be performed by using the light detection features implemented in liquid scintillation counting systems. When measuring 90Sr-90Y activity in urine by Chrenkov counting, most of the Cherenkov radiation is produced by 90Y (about 98.6%, Emax=2280kev) due to the lower energy of the beta particles from 90Sr (Emax = 546 KeV). There is no chemical quenching when employing Cherenkov counting, however, the counting efficiency varies strongly with color quenching, at a greater extent than in standard liquid scintillation counting, and therefore proper quench correction techniques must be employed. In a previous publication it was shown that a quench correction method based on the external source of some Liquid Scintillation systems can be applied. The method (named ESAR- External Source Area Ratio) uses an indicative parameter based on the integral area of the spectra, and it was shown that it is superior to the common methods which use conventional indexes. In the present work, the application of the ESAR method for determination of 90Sr-90Y in human urine samples is described. The design of a system that monitors the total activity released should address two main requirements: adequate sensitivity accurate report about the emitted activity. The sensitivity should comply with detection of very low concentration level of PET isotopes. In addition the report should provide an accurate estimation of the released activity based on the detector's gross counts reading and the air volume flow. These two requirements are in a contradiction. The best sensitivity is achieved by installing the detector inside the ventilation duct. On the other hand, correct release identification and accurate activity calculation, require a distant and shielded measuring point, where the effect of the shining filters or radioactive sources movement at the hot-lab can be reduced and even eliminated