The yield of ⁴⁷Sc at photonuclear production

⁴⁷Sc is considered as a promising beta-emitter for cancer radioimmunotherapy. Its practical application is hampered by the absence of a technology that could provide sufficient yield of the target isotope at a tolerant content of admixtures. A possible approach to settle this issue is a carrier-free ⁴⁷Sc production using a soft technology on the basis of the ⁴⁸Ti(gamma,p)⁴⁷Sc reaction in the field of high-energy bremsstrahlung radiation of an electron accelerator. In this work, the analysis of the key factors that determine the photonuclear yield of ⁴⁷Sc in a thick titanium production target is carried out. An analytical model providing the description of isotope generation in a thick target exposed to a spatially nonuniform flux of high-energy X-ray photons is developed. A set of main parameters of the process determining the total yield and distribution of activity in a target has been established. It is shown, that those parameters are the normalized coefficient of photonuclear conversion, the rms radius of photon flux density at a target, and also average annular divergence of the photon flux. The proposed approach is used for the optimization of geometry and activation mode of a cylindrical target from titanium. An independent study was conducted using a simulation technique on the basis of a GEANT4 transport code. The conditions of activation of targets from natural titanium in the electron energy range 30-95MeV are experimentally studied as well. It is established, that within the stated range of electron energy the yield of main scandium admixtures ⁴⁸Sc and ⁴⁶Sc are respectively by one and two order of values less than the yield of ⁴⁷Sc.The dependence of the ⁴⁷Sc gross and specific activity of a cylindrical target on its dimensions and electron energy has been calculated. In the case of a target from titanium enriched in ⁴⁸Ti and activation mode (40MeV; 0.3mA), the capacity of the photonuclear method amounts up to 1GBq/h ⁴⁷Sc at low content of by-products. (author)