The Research For Correction Factor Of X-ray Graphite Gavity Ionization Chamber

The topic of this research are the correction factor for the absolute measurement of the X-ray air kerma of the tube voltage from 250 kV to 600 kV.The air kerma as exports in the international system of units,it is one of the most important physical quantities in dosimetry of ionizing radiation.Correction factor is also a very important factor in the international comparison of the air kerma.The accurate measurement of the correction factor has important significance for the reduction of the uncertainty of the X-ray air kerma.Free air ionization chamber are widely used in the international comparison of X-ray air kerma first standard,the low energy(10-60)kV and middle energy(60-250)kV are two energy range X-ray air kerma benchmark which are established by using free air ionization chamber.The graphite cavity ionization chamber,on the other hand,is mainly used for 60Co(average energy 1.25MeV)and 137Cs(average energy 661keV)gamma radiation air kerma absolute measurement.In the gamma ray measurement is mainly using graphite cavity ionization chamber of high energy ray has better energy response and measurement can achieve very high accuracy and stability,and the measurement results of uncertainty is low,fully meet the quantity value transfer and traceability of requirements.Obviously,in the photon energy from 250 keV to 661 keV this period of energy range inner international comparison in gaps still exist,this topic is based on the existing maximum tube voltage 600 kV X-ray light tube,implementation(10-600)kV X-ray air kerma absolute measurement of meet the applications of X-ray in each energy range of medical diagnosis,protection,treatment and industrial on.The paper based on the National Institue of Metrology basic scientific research special "(250-450)kV X-ray air kerma research"(project number: 25-AKY1418-16),according to the graphite ionization chamber materials and structural design process,using EGSnrc simulation program to simulate the graphite cavity ionization chamber and the spherical-cylindrical chamber geometry structure,using BEAMnrc program to simulate 250kV-600 kV wide spectrum,narrow spectrum,high air kerma simulation of each of the three series of eight radiation quality X ray fluence spectra,finally usingEGSnrcMP simulation program respectively measure(250-600)kV X ray graphite ionization chamber the wall correction factor in different energy ranges.The beam radial non-uniformity correction factor,beam axis non-uniformity correction factor,chamber stem scattering correction factor and ionization chamber recombination loss correction factor are used experimental method to measure obtained,and ionization chamber humidity correction factor international commonly used in accordance with ionizing radiation measurement standards advisory committee CCEMRI(I)recommended value.In this paper the humidity correction factor with the recommended values.The spherical-cylindrical ionization chamber placed in(60-250)kV reference radiation field measurement.The X-ray air kerma values measured under the CCRI250 kV standard,and the deviation of the measured values of the air release kinetic energy from the reference value is 0.99%.The correction factor is used as the correction term in the formula of air kerma,and the deviation of the air kinetic energy to a certain extent also reflects the accuracy of the correction factor.The above research work,in a certain extent to establish(250-600)kV X-ray graphite cavity ionization chamber air kerma correction factor related research,laid a solid foundation for(250-600)kV X-ray graphite cavity ionization chamber air kerma first standard.It provides the basis for the international comparison of the X-ray and the quantity of the domestic and radiation protection and environmental monitoring.