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TUPSA36 |
The Unwanted Neutrons in Radiation Therapy During the Medical Electron Accelerator Operation | |
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| During radiotherapy using bremsstrahlung gamma quanta with energies greater than 8 MeV, nuclear reactions with neutron emission take place on the brake target and structural materials of a linear accelerator. Because of the high radiobiological danger of neutron radiation, especially fast neutrons, their contribution to the total beam flux substantially increases the dose received by the patient. We conducted studies of the braking gamma quanta and neutrons flows directly at the place of the patient's treatment at a distance of 1 m from the virtual source of gamma quanta with a radiation field size of 20x20 cm2. The use of direct spectrometric methods for measuring the flux of gamma quanta and neutrons in this case is extremely difficult due to the high flux density (according to some estimates ~1012 particles*cm-2*s). Therefore, for solving this problem, we used the photoactivation method. Registration of gamma quanta and neutrons was carried out using (gamma, n) and (n, gamma)-reactions. The natural tantalum 181Ta as one of the most studied nuclei in both photonuclear reactions and in reactions with neutrons in a wide energy range, was used as a detecting target. For the experiment, two Varian Trilogy medical accelerators with different operating life were used: accelerator 1 with long operating life (boundary energy 18 MeV) accelerator 2 with short operating life (boundary energy 20 MeV). | ||
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TUPSA37 |
Research of 89Zr Output in Photonuclear Reactions on Molybdene | |
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| In recent years, the use of electron accelerators for the production of radiopharmaceuticals has become important and relevant. One of attractive methods for non-invasive tumor detection and treatment planning is the positron emission tomography with radiolabeled monoclonal antibodies. Zr-89 has appropriate decay characteristics for high resolution PET imaging. Usually production of this nuclide is based on (p,n)-reaction on natural yttrium. However, proton accelerators are complex and power-consuming installations. They require a large number of specialists for their maintenance. At the same time, electron accelerators, such as microtrones, are more compact equipment and have undeniable advantages in ease of maintenance and energy costs. Therefore, we are conducting studies of the Zr-89 output in different photonuclear reactions. One of the perspective direction is the use of natural molybdenum as targets for these purposes. When the target is irradiated with high-energy gamma quanta, the short-lived nuclides Mo-89 (T1/2 = 2 min) and Nb-89 (T1/2 = 2 hours) are formed in the reaction (gamma, 3n) and (gamma, p2n), which decay into Zr-89 (T1/2 = 3.3 days). We irradiated the natural molybdenum target on the pulsed microtron with an electron energy 55M eV. The 50 mg target was irradiated during 80 minutes. The average current was 40-45 nA. The spectrometric measurements were carried out using a Canberra semiconductor spectrometer with a detector of high-purity germanium of large volume with an energy resolution 1.8 keV of 1332 keV Co-60 gamma-line. An activity of 240 ± 20 Bq was obtained. The Mo-99 gamma-ray transitions in the (gamma, n)-reaction at Mo-100 were observed in the spectrum. It was found that (gamma, 3n)-reaction cross-section amounts to (1,71±0,08)*10-2 of (gamma, n)-reaction cross-section. Obtained data is discussed. | ||
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