New results on proton-induced reactions on Vanadium for $^{47}$Sc production and the impact of level densities on theoretical cross sections

Abstract

New data for the nat V(p,x) reactions have been measured in the range 26-70 MeV, with production of the nuclides 47 Sc, 43 Sc, 44m Sc, 44g Sc, 46 Sc, 48 Sc, 42 K, 43 K, 48 V, 48 Cr, 49 Cr, and 51 Cr. The focus is on the production of 47 Sc, a β − -emitter suitable for innovative radiotheranostic applications in nuclear medicine. The measured cross sections for this radionuclide and its contaminants are compared with the theoretical excitation functions calculated with the TALYS code. In view of novel radiopharmaceutical applications, it is essential to accurately describe these cross-sections for the evaluation of yields, purities, and dose releases. Hence, we optimize the level-density parameters of the microscopic models in the TALYS code to obtain the best possible descriptions of the new data. We consider different irradiation conditions to estimate the production yields from the cross sections determined in this work. I. INTRODUCTIONThe theranostic radionuclide 47 Sc has gained the attention of the scientific community for its favourable decay characteristics (T 1/2 =3.35 days, E β − =162 keV, E γ =159 keV, I=68.4%)[1] that makes it one of the most attractive radionuclides for nuclear medicine applications [2]. In addition to its long half-life, suitable to follow the slow biodistribution of large molecules such as monoclonal antibodies, 47 Sc can be used for SPECT imaging, thanks to its γ-emission, and to treat small-size tumours, thanks to its high intensity low-range β − radiation. The stable coordination of Sc element with the chelating agent DOTA paves the way to new 47 Sc-radiopharmaceuticals, while the possibility to pair 47 Sc with its positron-emitter counterparts, 43 Sc and 44 Sc, permits also to perform low dose PET studies before, during, and after therapy [3][4][5]. Despite some promising preclinical results, the use of 47 Sc-labelled radiopharmaceuticals in nuclear medicine is curtailed by the lack of 47 Sc availability in sufficiently high yield and medically acceptable purity [6]. For this reason, all possible 47 Sc production routes are investigated worldwide, considering both accelerators (cyclotrons and LINACs) and nuclear reactors. The PASTA project (acronym for Production with Accelerator of Sc-47 for Theranostic Applications), aimed at measuring the most promising nuclear reactions to produce 47 Sc considering proton-beams [7,8]. The project was developed in the framework of the LARAMED program at the INFN-Legnaro National Laboratories (LNL), where a 70 MeV proton cyclotron was installed and the infrastructure for nuclear cross