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UBC Theses and Dissertations

Optimization studies of the TRIUMF biomedical pion beam Poon, Michael Nai-Chiu


Studies have been made to procure a flux-maximized and contaminant-minimized π⁻ beam for radiotherapy at the Batho Biomedical Facility at TRIUMF. The dependence of the pion yield on the incident proton energy bombarding the pion production target and on the mid-line momentum of the pion transport system have been measured. We have determined the transmission efficiency of the pion transport system: both its momentum and angular acceptance and also its phase space acceptance along the length of the target. Based on a sufficient understanding of the mechanism of gamma production from π° decay, a model has been made to account for the electron contamination measurements. An optimum π⁻ production target for radiotherapy is recommended. We conclude that the actual performance of the pion transport system is approximately three times below the design expectation. However, the reduced pion flux can be increased by changes in the present operating mode of TRIUMF. The incident proton energy should be decreased from 500 MeV to 450 MeV, where the expected proton current can be increased to between 220 and 450 μA by maintaining the cyclotron tank pressure between 1 x 10⁻⁸ and 5 x 10⁻⁸ torr. A 7.4 cm beryllium target, with its top surface exposed, would result in an eightfold decrease in the electron contamination if the proton beam were steered to the top surface of the target. With this operating mode, the maximum π⁻ flux at 2 00 MeV/c is expected to lie between 2.3 x 10⁸ and 4.8 x 10⁸ per second with a corresponding electron and muon contamination of 3% and 10%.

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