Monte Carlo simulation of 203Pb cyclotron production

The decay characteristics of 203Pb render it highly suitable for single-photon emission computed tomography (SPECT), while its properties also enable it to form a theranostic radionuclide pair with 212Pb. This study employs the Monte Carlo simulation method to model the bombardment of natural thallium, enriched 203Tl, and enriched 205Tl targets by a proton cyclotron. It investigates the influence of critical factors such as proton energy, beam intensity, irradiation time, cooling time, target thickness, and energy deposition on the production of 203Pb.The results demonstrate that, based on simulations using the TALYS program for proton irradiation of natural and enriched thallium targets, nuclear reaction cross-sections were simulated and compared with data from multiple sources. The FLUKA simulation program was utilized to explore the process conditions for 203Pb production by irradiating natTl, 205Tl, and 203Tl with a cyclotron. The findings indicate that the optimal incident proton energies for natTl, 205Tl, and 203Tl are 25 MeV, 25 MeV, and 11 MeV, respectively. The yield of 203Pb is linearly positively correlated with beam intensity, exhibits a nonlinear positive correlation with irradiation time, and increases with target thickness, eventually stabilizing within a certain range. Furthermore, an appropriate cooling time can effectively reduce the content of short-lived impurity radionuclides, thereby enhancing the purity of 203Pb. Finally, simulations using the SRIM program allowed for the calculation of proton beam energy attenuation within the target, clarifying the attenuation characteristics of the proton beam inside the material.