Abstract: As a radioactive nuclide activity detection technique with advantages such as high sensitivity, high detection efficiency, and simple operation, liquid scintillation measurement is widely used for measuring the activity of low-energy nuclides (e.g., ¹⁴C, ³H, and ⁵⁵Fe) in samples from the atmosphere, water bodies, soil, and biological specimens. During the measurement process, interference from background events (e.g., muons) leads to inflated results, thereby affecting the final analysis. To address the above problem, this paper proposes a dual-channel signal coincidence method to eliminate muon signals from background events. This method leverages the favorable signal time-preserving characteristics of fast-response photomultiplier tubes (PMTs). It marks the β signal output from the last dynode of the fast-response PMT and applies coincidence rejection to the muon signal. The marked β signal controls the switching of a gate, enabling the gating of the β signal output from the PMT anode. Experimental verification was conducted using ¹⁴C liquid scintillation samples. The results show a significant difference in the decay times between muon signals and β signals. The typical decay time for muon signals is 154.4 ns, while for β signals it is 41.6 ns. Specifically, muon signal decay times exceed 80 ns, whereas β signal decay times fall within the 10~80 ns range. The proposed method effectively eliminates muon signals. This research can serve as a reference for the accurate measurement of portable low-energy β nuclide activity.

Key words: liquid scintillation measurement technique, low-energy nuclides, muon, coincidence method