From simulation to experiment: multi-code modelling and validation of carbon-11 production using natural boron targets

Abstract

Abstract Background Carbon-11 is an essential radioisotope used in positron emission tomography (PET) for various applications in neurology, oncology and cardiology. Although a method for cyclotron production, based on the 14 N(p,α) 11 C reaction and using gaseous targets, is well established, alternative production methods using high-power lasers are sought. The 11 B(p,n) 11 C reaction with laser-driven accelerated protons is considered within the “Dr. Laser” project at Extreme Light Infrastructure–Nuclear Physics (ELI-NP). This study prepares the laser-driven production route by evaluation of the production of 11 C on three types of target materials: amorphous metallic boron (purity 95%), crystalline metallic boron (purity 98%) and boron nitride (purity 98%). The proposed approach integrates modelling of the excitation functions using the TALYS code with the evaluation of experimental irradiations performed at the TR-19 cyclotron at Horia Hulubei National Institute for Physics and Nuclear Engineering (IFIN-HH). The goal of this study is to assess the optimal target material and to investigate the dependence of produced activity on the incident energy of the 11 B(p,n) 11 C reaction. Results At an extracted proton beam energy of 15 MeV from the cyclotron, an effective incident energy on the target surface of 14 MeV was determined by evaluation of the proton transport through the experimental components, i.e. an aluminium window, a helium cooling layer and a sealing foil, using the SRIM/TRIM (Stopping and Range of Ions in Matter/Transport of Ions in Matter) code. By correlating this value with the simulated effective cross-sections, it is demonstrated that the energy fits into the optimal region of the excitation function for obtaining the maximum reaction yield. The experimental activities, corrected to EOB (end of bombardment), were found to be 7.77 GBq, 10.87 GBq, and 12.37 GBq for targets of amorphous metallic boron with purity 95%, crystalline metallic boron with purity 98%, and boron nitride with purity 98%, respectively. Experimental yields of 3.11 GBq/µAh, 4.35 GBq/µAh and 4.95 GBq/µAh were obtained for the three different targets, respectively. Although the measured values were 11.90% to 14.54% lower than the theoretical predictions, they demonstrated a strong correlation with the mathematical model. Sample quality analysis by gamma spectrometry confirmed an excellent radionuclide purity of over 99.9% for all three targets. Conclusions The 11 B(p,n) 11 C nuclear reaction at a proton energy on target of 14 MeV is optimal for 11 C production using solid natural boron targets. The boron nitride target provided the highest activity and yield values, a performance attributed to its higher apparent density and the contribution of additional nuclear reactions induced on nitrogen atoms, also resulting in 11 C. The radionuclide purity of the 11 C isotope obtained complies with the requirements of the European Pharmacopoeia, while the small but expected differences between the experimental results and the theoretical model validate the efficiency of irradiation on solid targets for the synthesis of high-purity radiopharmaceuticals. These results are to be implemented in the laser-driven nuclear reaction simulations and experiments.