Mathematical Calculation and Software Simulation of Positron Emitters Activity Concentration in a Duct

The Positron Emission Tomography (PET) method utilizes short half life β+ radioisotopes that are produced in a cyclotron site special for this purpose. The local radioactivity handling regulations in Israel, based on the International Atomic Energy Agency regulations, limit the activity concentration of radioactive isotopes in released air from hot zones, such as cyclotron vaults and production labs. For each radioactive isotope a Derived Air Concentration (DAC) limit has been set. A typical cyclotron site includes two main ventilation systems that need to be monitored: One from the cyclotron vault and the other from the hot cells located at the hot lab. The manufactured isotopes are β+ emitters: 18F, 11C, 13S and 15O. These radioisotopes emit a positron which produces, by annihilation, a pair of y photons in opposite directions, with energy of 511 keV. The radioisotopes half life is between 2 and 110 minutes. The activity of a single production batch can reach a value of up to 2000 mCi. In this paper a simple method of calculating the conversion factor, from measured cps of a 2'' cubic NaI(Tl) scintillation detector to activity concentration value in [Bq/m3], will be shown. This method can substitute the full calculations using MCNP program