Research And Application Of New Scintillator Detector In Detection Limit Of Ground-Space Nuclear Radiation

Gamma energy spectrum analysis plays a vital role in the application of nuclear geophysics.With the development of nuclear technology applications,a variety of gamma radiation detection systems have appeared.For different radiation detection systems and different application environments,it is important to choose the appropriate detector to achieve the best measurement results.Minimum Detectable Activity?MDA?is one of the important performance indicators of radiation detection systems.It is directly related to the detection capability and sensitivity of the radiation detection system,and is an important indicator to judge the adaptability and sensitivity of the detection system in a given measurement environment and application.At present,the calculation of the MDA is mostly carried out through experiments.Therefore,it is of great significance to carry out research on the MDA of detectors commonly used in gamma spectroscopy,and to achieve the effect of knowing the MDA value of any detector without performing experiments and simulations.This study can not only understand the performance differences of different detectors used in the measurement of gamma spectroscopy,provide a reference basis for the application selection of the detector,but also guide the gamma spectrum measurement to achieve better results.The study is based on the National key R&D plan"Deep ground resource exploration and mining"key special project"High-resolution aviation gamma spectrum measurement and airborne imaging spectrum measurement technology"?Project No.NO.2017YFC0602100?.The main purpose of this study is to compare the combination of five scintillator detectors including Na I,La Br₃,and Ce Br₃.The study includes a comparative study that combines a variety of experiments and MCNP5 simulation calculations.Three experimental methods have been designed:?1?Ground unshielded measurement experiment,used to simulate the change of the MDA in the daily land surface gamma spectrum measurement.?2?Ground low-background lead room shielding measurement experiment,used to simulate the change of MDA in the fixed measurement of radioactive samples,and provide a certain reference for the change of MDA in aerial gamma spectrum measurement.?3?Aviation gamma spectrum measurement experiment.On the basis of the experiments,the MCNP model is established,and the experiment and simulation calculation are organically combined to establish the mathematical model of MDA calculation.The research results show that the MDA of a detector for a certain energy is basically linear as the distance between the radiation source and the detector increases;For the same volume of La Br₃ and Ce Br₃,the La Br₃ detector is better than the Ce Br₃detector in daily land surface gamma spectrum measurement;the Ce Br₃ detector is better than the La Br₃ detector in the fixed measurement of radioactive samples and aviation gamma spectrum measurement.The large volume Na I detectors has high detection efficiency,does not have a radioactive background,and is more suitable for measurement scenarios with lower environmental background.The mathematical model of the detection efficiency changing with the crystal size is established by MCNP5 simulation data.The detection efficiency of l La Br₃ is about 1.30 times that of Na I of the same size,and the detection efficiency of Ce Br₃ is about 1.42 times of Na I of the same size.The simulated background is corrected by the experimentally measured background,and the mathematical model of MDA calculation is established,which basically achieves the effect of obtaining MDA without experiment.A preliminary MDA database for the data obtained from the MDA experiment has been established,and it is also applied to the UAV source finding simulation software;It also combines MDA with a nuclide identification algorithm to reduce false identification,and the algorithm has been applied to multiple gamma radiation measurement platforms.