Study On Radiation Field Of Heavy Ion Medical Machine

Nowadays heavy ion radiation therapy is one of the most popular method of radiation therapy,so the development of heavy-ion accelerators for medical use is also increasing.There is a large energy scale and a few fixed energy points for using in medical heavy ion accelerators.It is very interesting for studying the radiation field of medical heavy ion accelerators,such as in accelerator engineering and experimental research of heavy ion radiation therapy.And it is also important for the treatment process and maintenance staff.The radiation field of medical heavy ion accelerators includes instantaneous radiation field and induced radioactivity.The neutron field is the most meaningful physical parameters in the radiation protection of accelerator,which is the foundation for shielding design.The residual radiation is the most important source of the radiation exposure for maintenance workers.So the study of radiation field is the foundation of the radiation protection of accelerators.This paper is based on the radiation protection work of the medical heavy ion accelerator.The secondary neutron dose equivalent distributions were measured in the simulation cancer process with the carbon ions energy of 165 MeV/u,207 MeV/u,270 MeV/u and 350 MeV/u respectively.The induced radioactivity of the accelerator component was measured with the 300 MeV/u carbon ions bombarded on thick copper target,and the radionuclides were studied at different depth in the target.The Monte Carlo code was used in the paper for investing the instantaneous radiation field and induced radioactivity.In instantaneous radiation field the neutron dose equivalent distribution,neutron energy spectrum and energy deposition of light fragmentation was studied with fluka code.The study of instantaneous radiation field provide a basis for accelerator design,the assessment of additional dose for patients and etc.For induced radioactivity studying,the radionuclides in the target were measured with the HPGe gamma spectrometer,and then the experiments was simulated at the same condition,finaly validate measurement results with the simulation results.Then the induced radioactivity of accelerator components,cooling water and air was studied with FLUKA.Finally the induced radioactivity of various materials was studied.These studied have shown that the neutron dose and fragmentation dose are not very important during treatment.The activity of the induced nuclide is the largest at the end of the range in the target,and out of the range the same radionuclide is also detected.The activation of medical heavy ion accelerator components and targets is the most importan in the residual radiation field,while the effects of induced radioactivity in cooling water and air on the environment can be neglected.These basic parameters of calculation is useful for the environmental impact analysis and the assessment of individual dose received by staff,at the same time,they are very interesting for accelerator design and the material selection for radiation protection.There is few studies on the radiation field of heavy ion accelerator,and the experimental measurements and Monte Carlo simulations research in this area have a great reference value.These basement research provide the necessary data for the same type of heavy ion medical accelerator and the application of heavy ion cancer therapy in future.