Development of continuous measurement technology for low-concentration gaseous tritium based on solid scintillation fiber

Abstract The solid scintillation method has been employed to continuously measure low concentrations of gaseous tritium by simulating and validating the performance of unclad plastic scintillation fiber arrays. The Geant4 simulation software was utilized to model a fiber array with a fiber diameter of 0.5 mm, fiber length of 100 mm, and array diameter of 30 mm. The results demonstrated that with the spacing between fiber increased from 0.1 mm to 1 mm, the energy deposition probability of tritium decay electron decreased from 62.8% to 14% while effectively increasing detectable gas volume. Assuming a background count rate of 120 cpm for a 2 mm or 3 mm spacing, the array's lower detection limit was 4.1 Bq/L (100 min). The increased gas pressure leads to a decrease in the probability of electron energy deposition, but an expansion in detection volume continuously reduced the lower detection limit — reaching as low as 2.19 Bq/L at a 0.5 MPa pressure. By Increasing the array diameter to 125 mm, the lower detection limit with spacings of 0.2 mm and 0.5 mm reach values of 0.14 Bq/L and 0.23 Bq/L, respectively. Subsequently, a fiber array detector was designed with a fiber spacing of 0.5 mm, fiber length of 100 mm, and fiber array diameter of 50 mm. The measurement results demonstrated that the detection efficiency for gaseous tritium was about 9%, with an R 2 value of 0.9999 for the fitting response curve between counting rate and gaseous tritium concentration. The lower detection limit was 28 Bq/L (10 min). Considering that further optimization can be achieved by increasing the array diameter, it could be concluded that the detector based on unclad plastic scintillation fiber array holds significant potential for continuous measurement of low-concentration gaseous tritium.