Jinjie Wu

This study utilizes the monochromatic X-ray radiation device established by the National Institute of Metrology, China, to conduct a systematic experimental investigation of the mass attenuation coefficients of niobium, molybdenum, tantalum, and tungsten metals near their K absorption edges. The device's ability to generate continuously tunable monochromatic X-rays and accurately measure photon counts provides an ideal condition for precise mass attenuation coefficient measurements. This study employs a minimum energy step of 0.1 keV to systematically obtain the jump ratio rK and jump factor JK near the K-absorption edges of the four materials. The experimental measurements are compared with theoretical values from NIST-XCOM, NIST-FFAST, and Phy-x databases, demonstrating a consistent trend between the experimental and theoretical results, with relative deviations within acceptable limits, thereby validating the reliability of the theoretical models. An uncertainty analysis reveals a combined relative uncertainty of less than 2.7 %, indicating that the experimental results and theoretical values are in good agreement, with deviations and uncertainties within acceptable ranges. This research provides important experimental data and theoretical references for the application of monochromatic X-ray radiation devices in the field of mass attenuation coefficient measurements.

This work aims to measure the scattered radiation energy spectrum and radiation dose at different positions during radiological diagnosis through the Monte Carlo simulation and experiment. The results show that the average energy of the scattered radiation energy spectrum increases with the increase of the tube voltage and decreases with the increase of the scattering angle, but it changes very little with the measuring distance. It is not unified for the scattered radiation distribution in the space around the water phantom at the same tube voltage, and the exposure to scattered radiation is greater on the side closer to the water phantom or the X-ray tube. This indicates that the radiation exposure is not unified for medical staff in the scattered radiation field. The scattering energy spectrum and dose distribution are helpful to evaluate the scattered radiation exposure and enhance the self-protection awareness of medical staff in practice.

Accurate dose measurement is very important for diagnosing X-ray equipment. These equipment should be traced directly or indirectly to primary standard with as little uncertainty as possible. A parallel-plate free-air chamber was designed to measure air kerma of diagnostic X-ray absolutely. Different thickness of aluminium filters were used to obtain different radiation qualities according with IEC 61267. Correction factors were obtained by experiments and simulation, especially the air attenuation factor measured with vacuum method. The relative standard uncertainty of air kerma rate measurement was 0.46% and calibration factor was 0.53%. A transfer ionisation chamber was calibrated with Radiation Qualities in Radiation beams (RQR) qualities in National Research Council of Canada and National Institute of Metrology (NIM), the differences of calibration factors are less than 0.68%.

With the rapid application of nuclear technology, radiation protection is becoming more and more important. For external radiation protection, most of the national metrology institutes in the world have established the primary standard of X-ray air kerma in (10–250) kV and Cs-137 gamma ray, but the energy between 250 and 662 keV needs the establishment of traceability. To provide solution to such issue, a graphite cavity ionization chamber was constructed at National Institute of Metrology to measure the air kerma in (250–450) kV X-ray. The relative standard uncertainty of the method is 0.45%. Two different types of ionization chambers were used to measure the air kerma of N-300 radiation quality, and the result has a deviation of 0.09%.

Space scientific exploration is becoming the main battlefield for mankind to explore the universe. Countries around the world have successively launched various space exploration satellites. Accurate calibration on the ground is a key factor for space science satellites to obtain observational results. In order to provide calibration for various satellite-borne detectors, several monochromatic X-rays facilities has been built at National Institute of Metrology, P.R. China (NIM). These facilities are mainly based on grating diffraction and Bragg diffraction, the energy range of produced monochromatic X-rays is (0.218-301) keV. The facilities have a good performance on energy stability, monochromaticity and flux stability. Monochromaticity of all facilities is better than 3.0%, the stability of energy is better than 1.0% over 8 hours, and the stability of flux is better than 2.0% over 8 hours. The calibration experiments of satellite-borne detectors, such as energy linearity, energy resolution, detection efficiency and temperature response can be carried out on the facilities. So far we have completed the calibration of two satellites, and there are still three satellites in progress. This work will contribute to the development of X-ray astronomy, and contribute to the development of Chinese space science.

Absolute measurement of photon flux under high‐fluence rate X‐rays was required in photon diagnostics for X‐ray lasers. A free‐air ionization chamber used for the reproducibility of air‐kerma in high‐fluence rate X‐ray was designed, and the monoenergetic X‐rays flux of (6–20) keV were absolutely measured on Beijing Synchrotron Radiation Facility. The energy spectrum of the monoenergetic X‐rays was measured using a silicon drift detector, and the proportion of higher harmonics was determined. The saturation curve, air attenuation correction factor, and composite loss correction factor of the free‐air ionization chamber were obtained experimentally. The air‐kerma rate for the (6~20) keV monoenergetic X‐ray was measured accurately, and the relative combined standard uncertainty of the air‐kerma is 0.61%.

The energy spectrum is one of the most effective methods to characterise the quality of reference filtered X radiations. To obtain the energy resolution, the authors choose seven sealed standard radioactive sources to carry out energy calibration for high‐purity germanium detector whose energy resolution is within 3%. Then they use this spectrometer to measure the reference filtered X radiations with its energy from 55 to 125 keV of low air‐kerma rate series, meanwhile the BEAMnrc is used to simulate the spectra of the same four radiation qualities. By analysing the data of spectral distribution, they can determine mean energy and spectral resolution of these reference radiation qualities. By comparing simulation results with actual measurements, the result shows the spectra stimulated by the BEAMnrc are consistent with the spectra measured by high‐purity germanium detector and the deviation of the mean energy is within 4.0%. The spectral resolution of the reference filtered X radiation is 22.8, 22.4, 22.5 and 22.8%, respectively.