Design And Research Of Cylindrical Free Air Ionization Chamber

X-rays are short-wave electromagnetic radiation generated by extranuclear electrons and have strong penetrability.Therefore,since the discovery of X-rays,with the deepening and development of research,its application has penetrated into all walks of life.There are more and more applications in the medical field.With the development of society,people's living standards are increasing,and the incidence and mortality of cancer are rising rapidly.Among them,the number of breast cancer patients in China is increasing at a rate of 3%per year.Molybdenum target X-rays is an important method for early diagnosis of breast cancer,and excessive irradiation dose may induce breast cancer.Therefore,we must try to control the radiation dose of mammography to minimize the damage of radiation to the human body.As a gas radiation detector,the ionization chamber is particularly important for accurate reproducibility of air kerma.In this paper,the coaxiality and uniformity of the X-ray radiation field of molybdenum target are first measured.The results show that the uniformity of the radiation field at 60 cm from the radiation source is better than 99%,and the size of the radiation field is 55 cm,which meets the experimental requirements.Energy and efficiency calibrations were performed on the silicon drift detector.The measurement of the quality of the molybdenum target X-ray radiation was completed,and the results were consistent with the theoretical energy spectrum.In order to ensure the accuracy of the measurement data,a dual channel measurement software was developed based on the labview platform.Two channels measure the ionization chamber and the supervised ionization chamber ionization current.According to the supervised ionization chamber ionization current can effectively determine whether the ionization chamber stability is good.In addition,in order to control the volume of the ionization chamber,software for controlling the motor has been developed,and the piston connected to the electric shock can be controlled by software to change the volume of the ionization chamber.A new cylindrical free air ionization chamber was designed,machined and assembled.The physical design,mechanical structure design and processing assembly of the ionization chamber were completed.The ionization chamber performance was measured after the assembly was completed.The leakage of the ionization chamber is less than 1fA,and the impact is less than 0.001%,which satisfies the requirements of quantity recurrence.The various correction factors required to reproduce the kerma of the air were measured.The air kerma under each radiation quality in the different volumes of the ionization chamber was measured,and the transfer ionization chamber RC6 M 9066 was scaled.The uncertainty of the air kerma rate and the scale factor of the ionization chamber reproduced in the free air ionization chamber were analyzed.The relative standard uncertainty of air kerma rate is 0.21%(k=1),and the relative expansion uncertainty of scale factor is 0.56%(k=2).