BackgroundWhen performing gamma-ray spectroscopy analysis of samples with low levels of radioactive nuclide content, the weak peaks are difficult to be identified.PurposeThis study aims to propose a new method for identifying peaks in γ spectra by utilizing singular value decomposition (SVD) to improve the detection efficiency of weak peaks.MethodsFirstly, the matrix construction of spectrum data was improved by transforming the γ spectrum into a two-way cyclic matrix, and singular value decomposition of matrix was performed to get singular values and singular vectors. Then, the second singular value was selected to reconstruct the matrix and perform peak finding. Finally, the γ spectrum of the radioactive source 152Eu was used as the experimental object, the peak finding performance of proposed method was compared with that of first-order derivative peak finding, symmetric zero-area peak finding, and singular value decomposition peak finding.ResultsComparison result show that the bidirectional circular matrix SVD peaking method has higher recall rate, precision rate, and F1 value, achieving 100%, 87% and 0.94, respectively.ConclusionsThe approach of this study can optimize weak peak detection and offer additional options for peak finding methods.

BackgroundThe vanadium self-powered neutron detector (SPND) generates significant gamma noise current in the mixed radiation field of a nuclear reactor, which adversely affects the accuracy of neutron flux measurements and online monitoring of reactor core.PurposeThis study aims to explore the gamma effect of vanadium SPND through a combination of theoretical calculation method and experimental verification.MethodsFirst of all, a current component separation model was established according to the vanadium detector response mechanism, and the current calculation method of SPND in the pulsed research reactor was constructed. Then, multi-step Monte Carlo method was used to realize the coupling calculation of the core scale and the detector signal. Based on the temporal characteristics of different current components, the prompt γ current component was quantified by using the shutdown attenuation measurement experiment at the 200 kW radiation chamber of a research reactor. Finally, the measured signals were used to verify the sensitivity component separation model, and the dynamic response tracking and prompt γ current simulation capabilities of the detector numerical model were further verified by the vanadium SPND simulation of the commercial pressurized water reactor load rejection test process.ResultsThe established vanadium SPND calculation model can be used to effectively distinguish the detector response current component with a relative deviation of 2.27% for steady-state current calculation, and the calculated results agree well with the experimental data in terms of calculating the steady-state current and the prompt component of the steady-state current for the vanadium detector.ConclusionsThis study has shown that the gamma effect of vanadium SPND needs to be considered in both theoretical calculations and measurement analysis, and there is a mutual compensation effect among different current components in the gamma response of the actual reactor core.

BackgroundMeasurements of neutron energy spectra and doses during discharges of fusion devices are crucial for radiation monitoring and protection, and Bonner sphere spectrometers are generally used to measure neutron energy spectra and doses.PurposeThis study aims to investigate the neutron energy spectrum and dose equivalent of an Experimental Advanced Superconducting Tokamak (EAST) under experimental neutral beam injection (NBI) heating conditions.MethodsFirst, a Bonner neutron sphere spectrometer consisting of a 6Li-coated 4H-SiC semiconductor detector and eight moderated spheres was developed, and measurements in NBI heating and discharge experiments were conducted. Subsequently, the experimental results were normalized with the neutron flux monitoring results of the fission ionization chamber (ZZ3) on the EAST device and combined with the neutron response functions obtained from the Monte Carlo simulation for each moderated sphere. Then, the maximum entropy program was used to calculate the neutron energy spectrum distribution of the experimental positions inside the hall. Finally, the neutron dose equivalent at this location was obtained using the fluence dose conversion coefficient and compared with the neutron energy spectrum and dose equivalent at the corresponding location in the main hall, simulated using an existing EAST Monte Carlo model.ResultsComparison results show that the overall agreement between the simulated and experimental energy spectrum distributions of the measurement position is good, and the neutron flux at the measurement position under the normalized fusion neutron source is 1.38×10-7 cm-2, with a ratio of 0.98 to the simulated value. The surrounding dose equivalent is about 2.27×10-11 μSv, with a ratio of 1.05 to the simulated value, which shows consistency.ConclusionsThe results of this study demonstrate that the multisphere spectrometer is reliable for measuring neutron spectra and dose equivalents in the EAST hall and providing data for radiation protection in fusion devices. It can also provide a reference for neutron spectrum measurements in high-power fusion devices.

BackgroundHigh-purity Ge (HPGe) detectors are widely used in nuclear science, technology, and national defense because of their excellent energy resolution capability, which enables them to fingerprint gamma rays and accurately determine nuclide types and intensities. However, HPGe detectors typically need to be cooled to low temperatures for normal operation to prevent excessive thermal noise at room temperature.PurposeThis study aims to investigate the heat transfer process and temperature distribution law inside a HPGe detector to ensure the stable operation of the detector in a low-temperature environment.MethodsThrough the analysis of the heat transfer mechanism of the high-purity germanium (HPGe) detector, the internal heat transfer structure and a three-dimensional heat transfer model were constructed. COMSOL software was utilized to simulate the internal temperature distribution of the HPGe detector under liquid nitrogen refrigeration, as well as to investigate the effects of varying refrigeration times and packaging structures on this distribution. Based on these simulations, the packaging structure of the HPGe detector was optimized. Additionally, a temperature testing platform for the detector was constructed, and the simulation results were compared with experimental data to validate the model's accuracy.ResultsThe simulation results demonstrate that the detector model achieves dynamic equilibrium after 6 h of cooling, with the minimum internal temperature at the tip of the cold finger approximately -175 ℃. The utilization of oxygen-free copper as the cold chain material, combined with a low heat leakage and high-strength support material for the cold finger, enhances refrigeration efficiency. Additionally, the Dewar is designed with a sidewall thickness of 1.5 mm, and the spacing between the sidewall and the crystal cylinder is set at 3 mm. These design features collectively facilitate the detector's attainment of a lower limiting refrigeration temperature.ConclusionsThe modeling and temperature field simulation methods for HPGe detectors are validated through a consistency comparison between simulated and experimental data. Theoretical support is obtained for the further optimization and improvement of the design parameters of liquid nitrogen and electric cooling HPGe detectors.

BackgroundThe output signal quality of optical encoder in nuclear radiation environment is degraded due to the total ionizing dose (TID) effect of γ radiation.PurposeThis study aims to propose an improved adaptive line enhancer method (IALEM) that considers accuracy and efficiency to minimize the degradation of the output signal quality of photoelectric encoders in nuclear radiation environments caused by TID effect of γ radiation.MethodsFirstly, the Softsign function was introduced into the least mean square (LMS) algorithm to establish the nonlinear relationship between the error and the step size. Then, rapid convergence and small steady-state errors were achieved by introducing the previous step size value in the step-size-updating formula. Furthermore, this improved adaptive line enhancer method (IALEM) was compared with similar algorithms in terms of four aspects: convergence speed, steady-state error, low signal-to-noise input, and computational volume. Finally, the proposed algorithm was implemented in a field programmable gate array (FPGA) chip and verified on a photoelectric encoder platform, and its filtering effect was experimentally validated in a cobalt-60-source γ-radiation environment.ResultsThe results show that the proposed algorithm yields a higher convergence speed, lower steady-state error, and better filtering effect than that of other algorithms for low signal-to-noise ratio signals with less computational effort. Uniformity error and orthogonality error of the photoelectric encoder output signal after filtering by IALEM are reduced by 17.6% and 8.0%, respectively.ConclusionsThe experimental results show that the proposed algorithm can effectively filter out the noise generated through γ radiation and improve the output signal quality of the photoelectric encoder.

BackgroundIn recent years, the rapid advancement of nuclear energy and technology has led to the expanded utilization of special nuclear materials in more applications. In the pursuit of enhancing nuclear materials monitoring capability, extensive research has been dedicated to fast neutron multiplicity measurement systems based on liquid scintillation detector. However, these detectors are predominantly manufactured by foreign companies, such as Eljen and Saint-Gobain.PurposeThis study aims to evaluate the performance of a self-developed neutron detector based on EJ301 liquid scintillator.MethodsFirst of all, a 7.62 cm-diameter, 5.08 cm-thick liquid scintillator was applied to the development of neutron detector named EJ301-Z liquid scintillator detector, and 22Na and 60Co gamma sources were employed to calibrate this detector for establishing the relationship between incident particle energy and deposited energy. Subsequent tests on the neutron-gamma discrimination performance of the detector were conducted with a 252Cf neutron source, and figure-of-merit (FOM) values at different energy thresholds were calculated based on the charge comparison method. Then, comparison of the neutron-gamma discrimination performance of the detector with Eljen's EJ301 and Saint-Gobain's BC501A liquid scintillation detectors were conducted to evaluate the detector's performance relative to these commercially available models. Finally, the results obtained using the time-of-flight method were used to validate the results of the charge comparison method, providing an assessment of the absolute neutron-gamma discrimination performance of the liquid scintillator detector.ResultsThe experimental results show that, the EJ301-Z detect outperforms both Eljen EJ301 and Saint-Gobain BC501A detectors in terms of neutron-gamma discrimination, with an energy threshold of 150 keV, the rate of gamma mis-discrimination (RGMD) of EJ301-Z detector with the charge integration method is as low as 0.1‰.ConclusionsThe developed detector of this study demonstrates superior neutron-gamma discrimination performance compared to commercially available models from Eljen and Saint-Gobain.

BackgroundAviation γ spectrometer, measuring at high-altitude with low background counting rate, is prone to spectral line drift caused by factors such as long stable spectral periods and significant temperature effects due to its low background counting rate, hence seriously affects the accuracy of measurement results.PurposeThis study aims to propose an adaptive derivative-Gaussian joint peak search algorithm so as to quickly find and stabilize the peak value of airborne γ-ray spectrometer in low background environment.MethodsFirstly, the process of derivative peak finding algorithm was optimized so that it automatically determined the peak position, channel address, and left and right boundaries based on limited conditions, achieving adaptive transformation background window width deduction of Gaussian peak finding algorithm. Then, a self-developed miniaturized aviation γ spectrometer was used for flight measurement experiments by mounting it on unmanned aerial vehicle, and temperature changing measurement experiments by placing it in a variable temperature oven. Finally, the adaptive derivative gaussian peak finding results were compared and verified with that of traditional derivative peak-seeking algorithm and traditional gaussian peak-seeking algorithm, to ensure the accuracy of the proposed peak finding results and the efficiency of γ spectral stabilization.ResultsThe actual measurement results show that the adaptive derivative Gaussian joint peak finding algorithm has fast calculation speed and high accuracy. With 1 024 aviation tracks γ, the maximum spectral drift of the 40K peak measured by the energy spectrometer within the range of -20 ℃ to 50 ℃, does not exceed ±3 channels.ConclusionsThis study provides a new spectral stabilization method for the accurate measurement of airborne γ-ray spectrum in low background environment.