Novel wavelet threshold multi-point method for smoothing low-count gamma spectra

摘要: During the measurement of low- and intermediate-level radioactive waste (LILW), various factors can obscure weak peaks in low-count gamma spectra to different extents. Hence, before the gamma spectra of LILW are analyzed, these factors should be eliminated through effective smoothing. This study aimed to address the loss of weak peak information in gamma spectra due to the low energy resolution of LaBr₃(Ce) detectors during smoothing. For the first time, this study integrated the discrete wavelet transform (a transform that decomposes a given signal into a number of sets), Nyquist sampling rate (the lowest sampling rate that permits accurate reconstruction of a sampled analog signal), and fast Fourier transform (an algorithm that computes the discrete Fourier transform of a sequence). Through this integration, this study established an optimal criterion for the decomposition level, an adaptive threshold correction model, and a novel threshold function tailored to smoothing low-count gamma spectra. Experimental results demonstrated that the proposed method enhances the signal-to-noise ratio of an original gamma spectrum by 2.51 times. Compared with traditional methods, the novel method substantially reduced the root mean square error between the smoothed and original spectra by 87.1%, achieving this with a lower smoothness value. Furthermore, it mitigated channel distortions in the full-width at tenth-maximum for the characteristic peaks of the low-count spectrum by 75.0% to 96.9%. Under different peak distances, the peak-to-valley ratio of the overlapping peaks smoothed by the novel method increased by up to 7.4% compared with other methods. This method removes noise efficiently, preserves the original data of low-count spectra, and optimizes the peak-to-valley ratio of overlapping peaks. The results of this research
broaden the potential application scenarios of the LaBr3(Ce) detector in LILW measurements, as well as in other fields, such as regional geophysical exploration, radiation environment monitoring, nuclear medicine, and astrophysical measurements. It substantially reduces the cost of establishing measurement systems for low-activity radioactive materials in complex environments.