This work was aimed at developing a software for radioactive-source-free calibration of LaBr3(Ce) scintillator to detect the γ-rays from gaseous β+ annihilation in a Marinelli beaker. Based on a Monte Carlo model, a feasible method of numerical calculation was developed to calculate the detector efficiency. The results of the numerical calculation agreed well with the data obtained using the MCNP code. This is of the first steps in our research efforts to calibrat...