Abstract:
Objective The aim of this study is to establish a method for technical validation of X-ray equipment exemption in accordance with the principles of the exemption guideline, through experimental study on key specifcatons of radiaton dose measuring apparatus and Monte Carlo simulaton of shielding material atenuaton characteristc curves.
Methods Using a standard device of protective-level X-ray air kerma rate, the performance indices such as energy response and reading stability were tested for eight commercially available typical radiaton dose measuring apparatus with pre-set usage frequency, in the range of 10~60 kV loading tube voltage and under different tube current conditions, and calibration factor was also calculated. Simultaneously, the atenuaton characteristc curves of six frequentlyused shielding materials (lead, iron, aluminium, copper, tungsten, and polymethyl methacrylate) on X-ray were established by Monte Carlo simulaton.
Results
The eight radiaton dose measuring apparatus did not respond to X-rays below 10kV loading tube voltage. For 20 kV X-rays, six types of measuring apparatus responded, but the calibration factors of different apparatus were signifcantly different, ranging from 0.7 to 11.1. For 30kV X-rays, all apparatus responded, but the calibraton factors varied greatly. For 40 kV X-rays, all apparatus responded, and the calibraton factors of six types of measuring apparatus were closed to 1 without being affected by tube current. For 60 kV X-rays, the calibraton factors of all selected measuring apparatus were close to 1. Even the calibraton factor of the same type of apparatus varied greatly depending on the loading tube voltage, and not in a linear manner. Attenuation characteristic curves for 10-100 kV X-rays were established by Monte Carlo simulaton, and the curves were suitable for estmatng the ambient leaking dose equivalent rate of the X-ray equipment below 40kV shielded by materials with specifc thickness.
Conclusion A technical validation method is established for X-ray equipment exemption. For X-ray equipment with a loading tube voltage of 40 kV and above, exempton is granted according to the dose measurement results tested using apparatus meetng technical performance requirements and with corresponding energy category calibrated. For X-ray equipment with a loading tube voltage below 40 kV, exempton is granted according to the ambient dose equivalent rate at a distance of 0.1 m from any accessible surface of the X-ray equipment estmated by the proposed atenuaton characteristc curves.
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