Measurement And Study Of Ambient Dose Equivalent Of X-ray In Environmental Level

With the rapid development of nuclear technology in the fields of energy,industry,medical treatment,agriculture,national defense,scientific research and so on,the monitoring of radiation environment has attracted wide attention.In particular,after the Fukushima nuclear power accident,the public is particularly concerned about the monitoring and evaluation of the radioactive environment.According to Chinese environmental protection laws,nuclear power plants,radioactive sources and radiation devices such as ionizing radiation facilities need to be planned monitoring for radiation environment,to assess the radiation dose caused by radioactive environment for the public and radioactive practitioners,and assess abnormal radioactive release rapidly,and take emergency measurements when necessary.As a measuring instrument for compulsory verification,the radiation environmental monitoring instrument is a measurement problem that needs to be solved urgently.At present,the instruments from more than 200 radiation environment automatic monitoring stations have to be carried out the X and gamma ray verification and calibration in environmental level,the reaserch of X ray air kerma in environmental level will provide accurate and reliable traceability type evaluation for these instruments,which can make better use of the X ray in the low dose rate levels for the role of environmental monitoring and protect public health and safety.This paper relies on the national key research project“Reaserch on the metrology key technologies of extreme quantity in ionization and light radiation”?project number:2017YFF0205101?and measurement in low dose rate of X and gamma ray.It is also relies on central public welfare institutes for basic business subject“Measurement methods research on X ray air kerma in environmental level”and on the basis of?60-250?kV X-ray air kerma primary standard and?20-300?kV X ray radiation standard device in National Institute of Metrology.Firstly,the measurements of low dose rate were fully described about national laboratory.A set of half value layer measurement system is designed independently.Through a series of combinations of Pb,Sn,Cu and Al,established 7 X ray radiation qualities in environmental level and tube potential covers from?55-240?kV.The maximum deviation of the half value layer is 3.59%with the ISO 4037-1.The energy spectrum of the radiation qualities were measured by high purity germanium spectrometer,and the inverse solution of X ray pulse height spectrum to fluence spectrum was theoretically studied.Absolute measurement of X ray air kerma in environmental level was carried out by using free air ionization chamber,weak current measurement system,laser and position sensor system.And the correction factors in absolute measurement were studied by experiments and simulations,especially the measurement of front wall penetrating radiation correction factor is completed by the diaphragm designed.Then,the environmental monitoring ionization chamber was calibrated under the radiation qualities of high dose rate.We got the calibration coefficient of the ionization chamber in environmental level by interpolation,and completed the relative measurement.It has completed the comparison of the two methods under the L-100 radiation quality.The deviation is 0.8%,which was in the range of uncertainty.During the transfer process of X ray air kerma in environmental level,we completed the measurement and calibration of PTW 32003 spherical ionization chamber and high pressure ionization chamber,got the energy response.The complete curve of the energy response from low energy to high energy was obtained by calibration on ²⁴¹Am and ¹³⁷Cs radiation sources.We have completed the measurement from the high dose rate to the low dose rate range,and have calibrated and tested the radiation monitoring instruments for protection and environmental categories,and evaluated their performance indicators.At the end of the paper,X ray ambient dose equivalent in level of environment were also studied and discussed,and studied conversion coefficients of X ray air kerma to the ambient dose equivalent.The calibration of the energy response of FHT 192 high pressure ionization chamber and 451P radiation environment monitoring ionization chamber were carried out.The uncertainty of measurement results of air kerma were analyzed.The reaserch of X ray radiation in the environmental level was finished from the ionization current to the air kerma and to the ambient dose equivalent.