Design of a solid scintillation counter for tritium water measurement based on Ca2F(Eu) sheet using Monte Carlo simulation

Abstract

To measure the tritium concentration in water with an environmentally friendly way, a new detection method based on CaF2(Eu) sheet is being developed. The design of the detector is important in this method, and each basic unit of the detector consists of a pair of CaF2(Eu) sheets and a sample chamber for holding tritium water. The detector is coated with aluminum foil to avoid light and reflect scintillation photons which are received by a pair of photomultiplier tubes on both ends. The physical process of tritium water concentration detection was simulated by Monte Carlo simulation using the Geant4 tool kit. The energy deposition results in scintillator of electrons produced by tritium decay and the absorption probability of scintillation photons in sample chamber and scintillator were obtained in the simulation. The simulation results indicated that the thickness of the sample chamber had a major influence on detection efficiency, while the photon collection efficiency mainly depended on the thickness of the CaF2(Eu) sheet. The design of solid scintillation counter with multiple sample chambers can effectively improve the counting rate of the detection system. According to the simulation results, three types of detectors are designed, which have the characteristics of high detection efficiency, high counting rate and continuous real-time measurement capability respectively. Of the three types of detectors, type 2 detector has the lowest detection limit: 7.46 Bq/mL at a counting time of 10 min, and 2.95 Bq/mL at a counting time of 60 min.