Measurement And Research On Energy Spectrum Of Air-kerma Standard Radiation Field In Low-energy X-rays

The value of X-rays dose must be achieved trace to the source in order that the value of X-rays dose is unified, X-ray work measuring instruments are ensured accurately, consistently and used properly, the quality control of X-ray equipment must be ensured. The accurate, reliable and satisfying the requirements of reference radiation is established. It is the foundation that the quality control of radiation equipment is realized. Also, it is one of the basic work of standard laboratory.As one of the important physical quantity in ionizing radiation, air-kerma is the foundation of researching physical quantities in radiation protection. Also, it can be used as the important parameter of calculating absorb dose. The measurement and research on energy spectrum of standard radiation field in low-energy x-rays is a basis of the new state air kerma standard. There are several contribution on energy spectrum measurement and research for air-kerma standard. X-ray radiation quality, which can achieve value repetition, transfer, international comparison requirements, is ensured. It can determine tube voltage of X-ray machine in standard laboratory, the correct factor of the low-energy free air ionization chamber, Gy/Sv conversion factor in the instrument measuring of radiation protection. It fills the blank of the measurement of the filtered X-ray continuous energy spectrum in the domestic.Low-energy x-rays radiation device including low-energy x-rays machine, x-rays tube support platform and adjusting mechanism, shielding shell, aperture and shutter, supervision ionization chamber, radiation quality filter system, positioning device control systems, safe interlock systems, etc. Matrix ionization chamber is positioned in the reference position and the radiation wild is measured. The horizontal direction diameter is68mm when its heterogeneity is within1%, vertical direction diameter is91mm when its heterogeneity within1%. Radiation wild is measured by positioning matrix ionization chamber in different locations. The coaxial adjustment of the X-ray beam, aperture and shutter, the filter, positioning device is realized. The absorption piece of different thickness is placed in the middle of X-ray machine focus and the flat ionization chamber RC6M which measure the air kerma to get half value layer through the curve-fitting calculation.Low-energy type high purity germanium detector GL0110P is adopted to measure the energy spectrum of established low-energy x-rays air kerma standard radiation field. A series of factors influencing low-energy x-rays energy spectrum, such as x-rays tube voltage, current, the collimator device, the distance between the detector and the focus of the X-ray tube, how to place the detector, thickness of the additional filter, are measured and studied. Along with the increase of tube current, the forming speed of spectral increase, but shape remains the same. Along with tube voltage increasing, the FWHM, FWTM, Centroid increase correspondingly, namely the spectral lines grow wider and move to high energy. Spectral lines narrow gradually, and move to high energy as the collimator aperture is the decrease. Spectral lines remain unchanged when the detector is placed1.0m to3.5m from the focus of X-ray tube. The location of detector is limited by mechanical condition and the width of radiation wild. Energy spectrum is measured and analyzed when the detector move parallel up and down, left and right, and deflecting certain angle. With the additional filter thickening, continuous spectrum lines become narrow gradually and move to high energy, the effective energy of spectrum lines are improved, and x-rays qualitative become hard, the form of spectrum become more symmetrical.The accurate low-energy x-rays radiation device, the detector and the device geometry model are established through the Monte Carlo software EGSnrc. The energy spectrum of filtered X-ray are simulated based on that geometry model, and compared with the actual measured spectral lines. Because of the given simulation histories is restricted by simulation efficiency, the number of particles probing into detector is less, so there are certain statistical error. But measured spectral lines and the simulated spectral lines are consistent in the allowable error scope. The results show that the measured spectrum line is accurate. Another, several parameters affecting spectral lines such as the x-rays tube voltage and x-ray tube target materials, target angle, target thickness, target radius are simulated through the established low-energy x-rays radiation device model.