Design Study Of Neutron Monitoring System Of HUST-PTF

Cancer is one of the diseases which seriously endanger human health.Compared with tra ditional photon radiotherapy,the dose distribution of proton exhibits Bragg peak characteristic s,making the energy of the proton beam release at the cancer cells intensively when irradiatin g the patient.Due to the minimum damage to the healthy tissues surrounding the target tumor,proton therapy has the advantage of a precise treatment.Therefore,Huazhong University of S cience and Technology and China Academy of Atomic Energy hosted the National 13th Five-Year Key R&D Program"Development of Proton Therapy Facility based on Superconducting Cyclotron"（HUST-PTF）.During the operation of HUST-PTF,the proton beam may cause beam loss at the position of cyclotron,energy selection system,beam transmission line and treatment room.The protons interact with the nucleus in the target material,and secondary particles,including neutrons and gamma-rays,are produced in the process of nuclear coupling and nuclear de-excitation.The cascade neutron can penetrate the shielding wall of the workplace,interacting with the shielding material in the form of elastic scattering,inelastic scattering and nuclear reactions.Finally,a mixed radiation field of neutron and gamma rays is formed in the workplace.Excessive neutron radiation dose can induce various diseases of the human body,and also acti vate the accelerator equipment,causing irreversible damage.Therefore,it is necessary to dete ct neutrons in the areas of the workplace and establish a perfect neutron monitoring system to ensure the safety of equipment and personnel in the workplace.Neutrons are electrically neutral and difficult to be measured directly.At present,more neutron detectors use the nuclear reaction method to obtain the neutron dose indirectly through the measurement of secondary particles.According to the beam loss of HUST-PTF and the radiation field analysis,the optional commercial neutron detector cannot meet all areas’detection needs.The original model’s structural parameters were improved through the simulation of MCNP5 and FLUKA software,and the energy response and sensitivity were optimized.The optimized neutron detector can measure the neutron radiation in the energy range of 0.025 e V～250 Me V,and the dose equivalent sensitivity under the actual neutron energy spectrum can reach 43.5（count/s）/(μSv·h^-1).According to the layout of the neutron detector’s monitoring points,the article proposes the overall structure of the neutron monitoring system and details the design of the data acquisition system and the host computer system.An FPGA-based data acquisition system was independently designed,including a pre-level data processing circuit,a data acquisition unit and a power supply system.The software design methods of FPGA and embedded soft core were used to improve the system’s reliability.The algorithm of neutron leak count was compensated.A Lab VIEW software was used in the host computer system to build the system interface,which can meet each monitoring point’s needs.A data dynamic publishing query system was also designed using the Easy UI framework and JSP language,which can meet the needs of remote monitoring and historical dose data query.All parts of the monitoring system have been tested,and the test results meet the requirements of the radiation monitoring function,which can be stably operated.