| Gas targets are the most common form of target used in the production of short-lived radioisotopes for positron emission tomography (PET). Many researchers, however, have reported a non-linear relationship between radioisotope production yield and particle beam current. This lowered yield has been attributed to several factors including the scattering of beam particles into the target body walls, radioactive species becoming trapped in the target body walls, and gas density reduction due to the deposition of heat from the incident ion beam. In this study we investigate the last factor. A 13 MeV proton beam from the TRIUMF TR13 cyclotron was used to measure the energy of scattered protons in a gas target. The average proton energy reaching the target body walls was determined by measuring the ratio of radioactivity of two simultaneously produced radioisotopes in a metal foil lining the wall of the target. The relationship between the ratio of radioactivities and proton energy was determined using a stacked foil calibration technique. These experiments were compared to theory using a Monte Carlo program (SRIM) to model the interactions of a proton beam within a gas target. |
