The Research Of Molybdenum Target X-ray Cylindrical Free Air Ionization Chamber

With the continuous development of X-ray study and its application have been deep into the medical diagnosis, industrial flaw detection and processing and agricultural radiation breeding and other fields. Before using molybdenum target X-ray diagnosis of mammary gland, is one of the important methods of early detection of breast cancer. But excessive radiation doses, may also cause breast cancer. So breast photography, must try to reduce the radiation dose of breast tissue, lower the risk that may cause cancer to an acceptable level. So breast photography the correctness of the radiation dose measurement and evaluation, is for the medical behavior and the main factors of lower women’s breast cancer risk.Paper based on China metrology institute of scientific research conducted by the state administration of quality supervision, inspection and quarantine public welfare industry research projects of the molybdenum target X-ray benchmark establishment and the research of traceability system, design and processing of molybdenum target X-ray reference unit, set up in the IEC 61267 recommended molybdenum target X-ray radiation to reference quality, and to establish the radiation quality of the air kerma absolute measurement, the energy spectrum measurement; At the same time, a cylindrical free air ionization chamber was developed as a benchmark of molybdenum target X-ray ionization chamber, and completed the ionization chamber and correction factor of measuring various parameters.The thesis first of all, currently at home and abroad to establish benchmark of molybdenum target X-ray device and can carry out dissemination of radiation quality fully introduced. Designed to build a new set of benchmark molybdenum target X-ray device, implement the radiation beam, laser positioning, guide rail coaxial, conducted radiation field uniformity measurement study, and established the molybdenum target X-ray 25 kV,28 kV,30 kV,35 kV specification under radiation quality, measurement results are basically in ISO recommended value plus or minus 5%., set up a set of half value layer measuring system, processing and measuring the additional filter to cover the entire specification, through attenuation measurement method to complete the half value layer. Through measured half value layer, obtained the relevant effective energy radiation properties. Paper using liquid nitrogen refrigeration of low-energy high purity germanium spectrometer, carry on the accurate energy and scale efficiency, after finished the molybdenum target X-ray radiation spectrum measurement, measurement technology and solution had a further improvement and improve.In the paper the independent research and development design a cylindrical free air ionization chamber, completed the ionization chamber physical design, mechanical structure design and processing and assembling. Completed the ionization chamber leakage measurements, long-term stability and ionization chamber saturation curve measurement.Weak current measurement system are molybdenum target X-ray cylindrical free air ionization chamber to measure the air kerma inside a very important part. In the paper has developed a set of weak electric current was designed to measure the hardware system, can achieve high gain feedback/absolute measurement and current charge relative measurement. Through the combination of and measurement software, the accurate measurement of weak electric current is realized.In the free air ionization chamber measurement principle and weak current measurement method, on the basis of the related experiments design, completed the molybdenum target X-ray radiation quality specification under free air ionization chamber part modifying factor measurement. Finally realized the molybdenum target X-ray radiation quality specification of air kerma absolute measurement, the uncertainty of measurement results for the reasonable analysis and evaluation.The completion of the above work, a preliminary established the molybdenum target X-ray cylindrical free air ionization chamber of related research, in order to achieve the freedom of cylindrical air ionization chamber, became the basis for the molybdenum target X-ray provides technical support to the legal status of ionization chamber for international comparison of the value of molybdenum target X-ray specification and dissemination to the various domestic application provides the basis.