The Measurement And Research Of Reference Radiation Field For Diagnostic X-rays

With the increasing use of diagnostic X-rays equipment,more and more attention has been paid to the quality control of diagnostic X-rays devices.At present,many provincial metrology institutes regard diagnostic X-rays measurement equipment as a quality assurance tool for diagnosis of X-rays sources.The measurements of these devices should be traced directly or indirectly to the National Standards.The diagnostic X-rays reference radiation field is the standard radiation environment that is essential for the calibration of these quality assurance devices.The first is to meet the requirements of relevant standards which is relevant reference field,for diagnostic X-rays reference radiation field,and the second is to establish reference radiation quality of diagnostic X-rays,which is meet the relevant reference standards and procedures.A two-dimensional ionization chamber matrix is used to measure the coaxiality of the radiation beam,laser and the moving guide rail.Two methods are used to measure the uniformity of radiation field:1.A 0.125cm³ semiflex chamber was used to measure radiation field away focus 1m,and the result shows the radius which uniformity is better than 99%is85 mm;2.A Imagine Plate was uesd to measure once exposure under radiation field,and the result show that the uniformity of 99%is not Well-distributed.The results of the two methods are satisfied with the standard of ISO 4037?GB/T 12162?and could calibration of the diagnostic dose meter.Inherent filtration was measured by half-valued layer and measurement and the result is 0.101 mm Al,which meet the requirement of IEC 61267-2005 about the inherent filtration quality is not greater than 2.5 mm for the establishment of diagnostic X-rays radiation quality.Study on the non-intervention method of X-rays tube voltage measuring,and calibrated instrument of tube voltage.Comparing the result of it with the method of spectrum of end-point,showing the maximum relative deviation is not more than 0.6%.According to the requirements of the IEC 61267-2005,a half value layer fitting method is used to establish the RQR diagnostic X-rays reference radiation quality?RQR2^RQR9?,and meet requirements of this report.A X-rays tube model was established by Monte Carlo simulation software Beamnrc,and a series of RQR fluence spectrum obtained.Taking the fluence spectrum into the EGSnrc program to get the correction factors.The air kerma of diagnostic X-rays radiation quality was reproduced,and uncertainty was calculated.Comparing the air kerma of reproduced with calibrated diagnostic X-rays chamber,the most deviation is 0.5%.The sources of the uncertainty of the free air ionization chamber are analyzed in detail,and the standard uncertainty is 0.22%.The results of measurement shows that the diagnostic X ray reference radiation field has preliminarily reached the requirement of quantity transfer.