The Study Of Lanthanum Bromide Detector’s Intrinsic Radioactivity And Its Impacts On The Detection Limit

In recent years, with the continuous development of nuclear energy and nuclear technology application, the requirement for complex γ-ray spectrometry measurement and analysis is also on the up and up. At present, the domestic use of gamma ray spectrum measurement system is mostly based on NaI(Tl) detector and HPGe detector.The Na I(Tl) detector’s energy resolution is low, unable to analyze the type and content of radionuclides in the complex γ spectrum. Although the HPGe detector has a very good energy resolution, but its detection efficiency is very low, needed liquid nitrogen to refrigerate, costing too much, not easy to carry. The new halide scintillator Lanthanum Bromide Detector has attracted particular attention with its good energy resolution(<3%@ 661.7KeV) and fast response time and high detection efficiency.it can replace the traditional Na I(Tl) detector in many cases. Since carrying natural radionuclides 138 La and 227 Ac, the Lanthanum Bromide Detector with high intrinsic radiation background. In order to make better use of Lanthanum Bromide Detector, we must calculate its intrinsic radioactivity accurately especially at low background environment is of great significance.In gamma spectrum measurement, the Lanthanum Bromide Detector’s intrinsic radioactivity and environmental radioactivity are the important parts of the gamma spectrum. The intrinsic radioactivity will have a direct impact when making qualitative and quantitative analysis for the gamma spectrum of low radionuclide content and activity. Therefore,in order to reduce the interference of the intrinsic radioactivity measurement results and obtain effective net peak counts of the sample, it is needed to smooth the spectrum and subtract the background of the measured spectrum and calculate the contribution of the intrinsic radioactivity in the environment.At the same time, in order to further explore the Lanthanum Bromide Detector’s ability to detect low levels of radionuclides, we will calculate the minimum detectable activity(MDA) of Lanthanum Bromide Detector’s intrinsic radioactivity for the low radionuclides.The study is based on to the Ministry of science and technology major scientific instrument and equipment development projects(project number: 2012YQ180118). Based on the research of Lanthanum Bromide Detector’s basic characteristics and a variety of of the detector background subtraction methods, The main research contents and achievements of thesis are as following:1) Do some reasearch on the energy resolution, temperature characteristics, intrinsic radioactivity and other basic features of the Lanthanum Bromide Detector’s detector.2) Making some analysis and comparison of different background subtraction method for the gamma spectrum background based on the Lanthanum Bromide Detector’s intrinsic background radiation spectrum. A new improved adaptive SNIP background subtraction algorithm has been proposed.Calculating and analysing the influence caused by the Lanthanum Bromide Detector’s intrinsic radioactivity for the natural radionuclide 40 K.3) Analyzing the gamma spectrum of the radioactive source 133Ba、241Am、137Cs、60Co、152Eu in the natural environment and low background lead chamber with the improved adaptive SNIP background subtraction algorithm. The contribution of the Lanthanum Bromide Detector’s intrinsic radioactivity to the total peak of various radionuclides was studied in the natural environment. The minimum detectable activity(MDA) of the Lanthanum Bromide Detector under natural environment conditions for each point source is calculated.