| ? photon,commonly known as ? ray,also called ? particle flow,is an electromagnetic wave which the wavelength is less than 0.001 nm.? ray is produced during the energy level transition.As the measuring instrument of ? ray,? photon detector is widely used in the military and civil economy fields.It is the most important tool in protecting the nuclear facility,nuclear device and ? ray application device.Moreover,it is the ensurance for avoiding the nuclear leakage and calming the panic caused by nuclear blackmail.So far,the common portable ? photon detectors are usually sent to a fixed calibration facility equipped with a standard radiation reference(SRR)for calibration.However,the distances between the calibration facility and instrument users are more than hundreds or even thousands of kilometers in common,the calibration period is usually more than weeks with a low efficiency.For ? photon detectors fixed installed in a nuclear facility cannot be dismounted integrally for calibration,only substitution method can be employed for calibration.According to the substitution method,a radiation source with low activity is used to irradiate the probe of the detector,then the performance of the detector is judged by the response of the indicate value.Due to the low activity of the radiation source,the middle or high range of the detector is unable to be calibrated with this method.Moreover,the interference from environmental scattering ? rays are neglected.Therefore,the performances of the detectors cannot be calibrated and evaluated scientifically.This dissertation is supported by the basic laboratory research project of Chinese Academy of Engineering Physics named “Study on key technology of ? ray air kerma determination in field”(No: JW20*2005043),and the fundamental research of National Defense Science and Industry Technology named “Development of the field calibration device for ? rays air kerma used in the radiation protection field”(Project Number: 622).With these funding,we carried out the research on the field calibration theory,device,method and techniques for ? photon detectors based on a minitype reference radiation(MRR).Then we developed an in-situ calibration device for ? photon detectors used in radiation protection field.The main contents in this thesis are as follows:(1)Described the domestic and foreign research status of the calibration methods for ? photon detectors,especially for fixed installed ? photon detectors.Based on the detailed comparative analysis of the existing calibration methods and the study on key technologies of the field,on-site and in-situ calibration methods,this thesis studied the principles and methods of in-situ calibration technology for ? photon detectors based on MRR.This thesis also studied the determination of the ? ray air kerma conventional true value at the point of test in an MRR and the machine prediction methods based on experimental samples,which established foundation for the research of this paper.(2)Carried out the research on the construction of the MRR and the feature of the dose field.According to the analysis of the calibration theory for ? photon detectors based on the MRR,feasible MRR was built up.Moreover,research on the feature of the dose field in MRR was carried out based on Monte Carlo simulation,which provided the theoretical support for the field calibration.(3)Studied the feature extraction method of scattering ? spectrum based on wavelet analysis and principal component analysis(PCA).Scattering ? spectrum was affected by the noise and the excess data.In order to solve this problem,wavelet analysis was applied to denoise the noise.Then PCA was applied to extract the feature components.The dimension of the modeling data was decreased significantly.The prediction precision of the air kerma conventional true value was improved significantly.(4)Carried out the study on optimizing the determination model of ? ray air kerma in the MRR based on random black hole combined progressive particle swarm optimization algorithm(RBH-PRO-PSO).The prediction model of the ? air kerma conventional true value was trained by least square support vector machine(LSSVM)with the sample data.In the study,RBH-PRO-PSO was applied to optimize the prediction model.Compared with traditional PSO,black hole or other algorithms,the globally optimal solution of was RBH-PRO-PSO excellent.The measuring accuracy of the determination model of CAK in an MRR optimized by RBH-PRO-PSO was better than other algorithms.(5)Studied the energy response correction theory and method of the detector when the field calibration technology for ? photon detector based on MRR was in practical application.By analyzing the energy response curves of different detectors and the accepted ? spectra,the energy response correction factors of different detectors were calculated.In the practical application,the energy response correction factors were applied to correct the energy response of different detectors empirically and then corrected the calibration results.(6)Developed a field calibration device for ? photon detector based on MRR and tested the performance of the device.Carried out the uncertainty evaluation and research work of the field calibration device based on MRR.Measuring error sources in the calibration process were analyzed,then the uncertainties of each error source were evaluated discreetly.At last,evaluated uncertainty of the field calibration device was 4.57% and the expanded uncertainty was 9.14%.This research work involved ? ray dosimetry and it was related to the radiation protection and nuclear security.This paper was the first to propose the field calibration theory and techniques for ? photon detector based on MRR and develop a field calibration device for ? photon detectors around the world.This paper also proposed a new technical idea for the development of field calibration technology for ? photon detectors which provided a new demonstration device for ? photon detectors calibrated on-site or in-situ. |
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