Powerful electron accelerator for the production of neutrons and radioisotopes
The purpose of the work is to study the possible use of existing high-power electron accelerators for neutron therapy and the production of radioisotopes. Calculations were performed for both applications and the results were normalized to the characteristics of the existing MEVEX accelerator (average electron current 4 mA at a monoenergetic electron beam of 35 MeV). A unifying problem for the applications is the task of cooling the target: at a beam energy ~ 140 kW, almost half of this energy is released directly into the target. Therefore, a liquid heavy metal was chosen as a target in order to combine the high quality of thermohydraulics with the maximum performance of both bremsstrahlung radiation and photoneutrons. The targets were optimized using precision codes for radiation transfer and thermal-hydraulic applications. Optimization was also carried out on the installation as a whole: (1) on the composition of the material and the configuration of the photoneutron removal unit for neutron capture therapy (NCT) and (2) on the bremsstrahlung generation scheme for producing radioisotopes. The photoneutron unit provides an acceptable beam quality for NCT with a large 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 existing and planned reactor beams. Such intensity at the beam output will make it possible to abandon fractionated irradiation in many cases. As for the production of radioisotopes, in the calculations for the (γ, n) reaction, 43 radionuclides in five groups were obtained. For example, using the Mo100(γ, n)99Mo reaction, it is possible to obtain the 99Mo precursor of the main diagnostic isotope 99mTc with a specific activity of ~ 6 Ci/g and a total target activity of 1.8 kCi after irradiation for 24 h. The proposed schemes for generating and outputting photoneutrons and bremsstrahlung have a number of obvious advantages over traditional methods, including: (a) the use of electron accelerators for producing neutrons is much safer and cheaper than the use of reactor beams; (b) the accelerator with the target and the beam output unit with the necessary equipment and tooling can be easily placed in a clinic; and © the proposed liquid gallium target for NCT, which also serves as a coolant, is an «environmentally friendly» material: its activation is relatively small and drops quickly (after about four days) to the background level.
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