Alpha Spectrum Resolving Method Based On The Detector Response Function

Alpha particle beam measurements are an important means of alpha nuclideanalysis, and it includes the total radioactivity measurements and alpha spectrummeasurements. The former can only obtain the total activity of nuclides, but cannotdistinguish alpha category and determine the energy and distribution of particle beam.The alpha spectrum measurements can detailedly classify the alpha particles withwhose energies and then achieve the number of different energy alpha particles.Therefore, in order to accurately obtain the level of radioactivity in various alphasamples, it become particularly significant with alpha spectrum measurements andanalysis.The regulation and classification of transuranic radionuclides(such as239Pu,241Am,et al) In nuclear waste disposal, as well as alpha radioactive aerosol monitoring in somespecial places, often take use of alpha spectrum measurements. Although the ratiobetween isotopes can be accurately measured by a mass spectrometer, it is the mosteconomical and fast way to obtain reliable results by alpha spectrum analysis. In thesituation of detector’s limited energy resolution, it is an essential process to resolvespectra to accurately analyze the type and level of radioactivity, while it is also difficulty.So far, domestic and abroad researchers never stopped studies of alpha spectrumresolving analysis technique, in which peak shape function selection has become thefocus. Almost every alpha radioactivity nuclides have multiple energy, and energies aresimilar between the same or different nuclides. The current detector, even the bestenergy resolution of semiconductor probe device, cannot be completely separated theseenergies. Therefore, when one analyzing the overlapping alpha spectrum, establishingpeak shape function is important. Moreover, peak shape functions rely on the so-calledpeak shape parameter, the value must be optimized by the fitting procedure. In general,the more amount of parameters can reach better results, but it also badly exacerbatedoptimizing difficulty and stability, so it is crucial to determine the parameters values forwhether the peak shape functions can accurately resolve the energy spectrum. This paper, focusing on the key issues from the above mentioned alpha spectrumtechniques on the basis in-depth studying of domestic and foreign predecessors, issupported by National Natural Science Funds for Distinguished Youth Scholar of China(41025015) and the National Natural Science Foundation of China (41374130). Andthis paper carried out alpha spectrum measurements and alpha spectrum resolvingresearch based on Passivated Implanted Planar Silicon Detector (PIPS) and modelsbased on the detector response function.The main contents and results of the paper are as follows:(1) Alpha spectrum measurement of239Pu and241Am using the PIPS detector atdifferent vacuum and geometric factors, then qualitative study the impact on energyresolution and detection efficiency with different factors.(2) Applying the discrete wavelet transform (DWT) in the signal processing toalpha spectra smoothing, and proposing a new method to assess the effects of smoothing.The results showed that discrete wavelet transform method is better than the traditionalpolynomial least squares method for low-level, high noise alpha spectrum.(3) On the basis of in-depth study on the mechanism of alpha spectrum formationfor PIPS detection system, a detector response function model is established. The modelis then applied to resolve239Pu and241Am spectrum under different vacuum andgeometric. The results shows that the detector response function is a good choice foralpha spectrum analysis. The parameters of alpha spectrum detector response functionis determine by self-developed fitting procedure based on the nonlinear weighted leastsquares.(4) Depending on the previous algorithms study, this paper using MATLAB-GUIplatform to develop alpha spectrum analysis software as off-line spectrum analysis. Ithas an intuitive interface and good functions, and makes up the defects of measurementsoftware of alpha spectrometer which cannot resolve the complex alpha spectrum.In conclusion, this paper carries out basic research, and there are certain methodsand technology innovation, and ultimately achieve the purpose of alpha spectrum for amore accurate solution, but in the process of resolve spectrum, I deeply understand thatthe selection of initial parameters to detector response function affecting the analyticalresults on the stability as well as the pros and cons of the model. These studiesaccumulated a lot of experience for spectrum automate analysis of alpha complexspectra in the future, and it has much reference values.