Производство фотонейтронов и радиозотопов для медицины тормозным излучением на промышленных электронных ускорителях

Abstract

Purpose: To study the binary possibility of using the available linear electron accelerators for the neutron therapy and radioisotopes production. For both applications, calculations were performed and the results were normalized to the characteristics of the Mevex accelerator (average electron current 4 mA at a monoenergetic electron beam 35 MeV). It turns out that the production of both photoneutrons and radioisotopes is effective when using bremsstrahlung radiation generated in the giant dipole resonance of a heavy metal target.
 Material and methods: The unifying problem for both applications is the task of target cooling: at beam power ~ 140 kW, half of it or more is deposited directly in the target. Therefore the liquid heavy metal was selected as a target, in order to conjoin high thermohydraulics quality with maximal productivity both bremsstrahlung radiation and photoneutrons. The targets were optimized using precise codes for radiation transport and thermohydraulics problems. The optimization was also carried out for the installations as a whole: 1) for the composition of the material and configuration of the photoneutron extraction unit for neutron capture therapy (NCT) and 2) for the scheme of bremsstrahlung generation for radioisotopes production.
 Results: The photoneutron block provides an acceptable beam quality for NCT with a high neutron flux density at the output ~2·1010 cm–2s–1, which is an order of magnitude higher than the values at the output of the reactor beams that worked in the past and are currently being designed for neutron capture therapy. As for radioisotopes production, using optimal reaction channel (γ, n) 43 radioisotopes in 5 groups were received. For example, by the Mo100(γ,n)99Mo reaction the precursor 99Mo of main diagnostic nuclide 99mTc with specific activity ~6 Ci/g and total activity of the target 1.8 kCi could be produced after 1 day irradiation exposure.
 Conclusion: The proposed schemes of neutron and bremsstrahlung generation and extraction have a number of obvious advantages over traditional techniques: a) the applying of the electron accelerators for neutron production is much safer and cheaper than to use conventional reactor beams; b) accelerator with the target, the beam output unit with the necessary equipment and tooling can be placed on the territory of the clinic without any problems; c) the proposed target for NCT is liquid gallium, which also serves as a coolant; it is an “environmentally friendly” material, its activation is rather low and rapidly (in ~4 days) falls to the background level.