As an ideal tracer gas in atmospheric science, radon plays a crucial role in elucidating the mechanisms governing its atmospheric concentration, which holds significant research importance. This study conducted continuous radon monitoring in Beijing to investigate its diurnal and seasonal variations, as well as its correlations with meteorological factors. Radon concentration exhibits a characteristic diurnal cycle with daytime diffusion and nighttime accumulation, a pattern largely attributable to temperature inversion. Additionally, radon concentration exhibits cyclical variations every 5-10 days, corresponding to medium-term atmospheric circulation patterns. Average radon concentrations ranged from 5.61 to 8.71 Bq·m-3 in spring and summer, and from 7.71 to 11.86 Bq·m-3 in autumn and winter. Furthermore, a positive correlation exists between radon concentration and relative humidity, while a negative correlation is observed with ambient temperature. These correlations are weaker in spring and summer and stronger in autumn and winter. A 1 h lag in radon concentration changes is evident relative to both relative humidity and temperature, with the correlation reaching a maximum at this lag time. The results of this research enhance the understanding of atmospheric radon concentration dynamics and provide a solid scientific foundation for developing a short-term prediction model of radon levels based on meteorological parameters.

Radioxenon isotopes monitoring is of interest to the international monitoring system (IMS) of the comprehensive nuclear-test-ban treaty (CTBT). In the current IMS, the beta-gamma coincidence system utilizing plastic scintillator detectors and HPGe detectors achieves the best minimum detectable activity. PIPSBox detectors have outstanding advantages of higher energy resolution and a lower "memory effect", which may offer a new option for beta detectors in IMS. A dedicated high-resolution beta-gamma coincidence system has been developed in CNL06 referring to the Spalax next generation system. Commercial PIPSBox detector measurements with four radioxenon isotopes were performed at two different facilities with different background conditions.

Bayesian source reconstruction is important to trace the atmospheric radioactivity emissions in both unintended and accidental scenarios. The likelihood function is a key component of Bayesian reconstruction determining its performance. In this paper, Bayesian methods using different likelihood functions and parameterization schemes were evaluated based on the European Tracer Experiment (ETEX), including 27 different likelihood functions that involves the combination of Gaussian, log-Gaussian and log-Laplace functions and 9 parameterization schemes. 100 test data sets were randomly sampled from the observation network of ETEX and the 27 likelihoods were applied to each of the 100 data sets. The performances of 27 different likelihood functis were compared based on the posterior distributions of the reconstructed parameters in individual reconstructions and the statistical distribution of errors across the 100 tests using Nemenyi tests. Results show that likelihood functions have significant influence on source estimation. Gaussian likelihood is the most sensitive to the parameterization scheme. But it presents a good location accuracy, while the deviations are below 0.3 degrees, if appropriately parameterized. The log-Gaussian and log-Laplace likelihoods exhibit comparable reconstruction performance and show less sensitive to scale parameters than Gaussian likelihoods. The above information provides an insight into the reconstruction design and the parameterization in practical applications.

Four radioxenon isotopes are key radionuclides in nuclear explosions monitoring under the Comprehensive Nuclear-Test-Ban Treaty verification regime. Due to the high sensitivity of the (-gamma coincidence method, it is widely used in International Monitoring System radionuclide station equipment. Plastic scintillation detectors and HPGe detectors are one option, with some technological issues that need to be addressed. In this work, a plastic scintillation detector based on a silicon photomultiplier tube (SiPM) array readout is developed, and the essential performance is evaluated. The SiPM-based detector is compact and can be applied successfully to mixed radioactive xenon measurement.

Inversion for the radioactive source term has received growing attention in the post-Fukushima era. Under some special scenarios, the source term, including release rate, height and position, is necessary for nuclear emergency response and consequence assessment. Here, a transformer-based deep learning architecture was developed for multivariable source term estimation. The CALMET-LAPMOD coupling model validated by the Kincaid tracer experiment was employed to produce the datasets. The datasets were systematically constructed for five representative scenarios with the following time-varying parameters: release rate, release height, release location, coupling of release rate and height, and coupling of all three variables. Subsequently, a Transformer model with Bayesian optimization for adaptive hyperparameter tuning was developed. The results demonstrated excellent performance in source term inversion, with a determination coefficient (R2) of above 0.96 for release rate and height, and an average distance error of 1.19 km at a 95 % confidence level for location prediction. Regarding the coupling of all three variables scenario, the R2 for release rate and location remained above 0.92, whereas the height achieved R2 of 0.72. Additionally, feature ablation analysis revealed that monitoring points with high concentration values contribute significantly to inversion, providing quantitative insights to optimize the monitoring network layout.

A β-γ coincidence system for radioxenon measurement with high detection sensitivity has been developed in Beijing Radionuclide Laboratory by using a broad energy germanium γ-detector and a plastic scintillator β-detector. In order to further improve the performance of the system, a cosmic-ray veto detector system has been implemented to reduce the background induced by cosmic-ray muon. This paper reports on the setup and commissioning of the anti-cosmic β-γ coincidence system. In a 24-h measurement of the system, the Minimum Detectable Activity (MDA) for 131mXe, 133mXe, 133Xe and 135Xe have been estimated to be 0.9 mBq, 1.1 mBq, 2.2 mBq and 2.1 mBq respectively.

41Ar是反应堆和加速器运行释放到环境中的主要放射性核素之一，具有半衰期短的特点。由于β-γ符合法能显著降低本底、提高探测器灵敏度，为了实现41Ar高灵敏度测量，设计了由BC404和CsI(Tl)组成的β-γ符合闪烁体探测器，并建立了以最小可探测活度浓度（Minimum Detectable Activity Concentration，MDC）为优化目标的探测器结构优化方法。首先，运用Geant4对β射线在CsI(Tl)中的泄漏率进行模拟，选择BC404厚度为3 mm，此时泄漏率为0.73%；其次，对不同的气体腔尺寸进行模拟，分析计算β探测效率、γ峰效率、气体腔体积和取样时间对MDC的综合影响，完成探测器的结构优化；最后，分析了本底计数率和测量时间对MDC的影响。当测量时间为200分钟、处理时间为30分钟、本底计数率为5×10-3 cps时，优化后的探测器对41Ar的MDC估算值为1.7 Bq/m3。

As a passive nondestructive nuclear technique,gamma ray spectrometry is used in many radioactivity laboratories.Gamma-ray spectrometry enables the identification of radionuclides in a sample from their emitted photon energy and calculation of their activities from the number of photons collected for each energy.However coincidence summing effects will influence the reliability of both radionuclide identification and calculation of activity.Coincidence summing effects appear when sources emitting coincident gamma rays are measured via gamma-ray spectrometry.Those effects that result in losses from the full energy peaks and enhancement of sum peaks influence the accuracy of the spectral analysis.To eliminate this influence,many correction methods have been established.Research on the coincidence summing effect(CSE)originated in the 1960s.Subsequently,many algorithm-based generation mechanisms of CSE have been built together with the development of corresponding correction software.Massive amounts of technological information on and achievements about coincidence summing correction have been reported by researchers from different countries,hence several intercomparisons of these methods,and self-consistency testing of cascaded additive effect correction algorithm were organized by the International Committee for Radionuclide Metrology(ICRM).Based on a detailed summary of the development history of correction methods,the CSE mechanisms,correction algorithms,correction software,and application of correction techniques were reviewed in this paper.Cobalt-60 was taken as an example to illustrate the influence of the summing-in and summing-out effects,with correction equations based on different measurement geometries and considering the impact of angular correlations.Meanwhile,the performance of different algorithms and software were compared and analyzed.Combined with the current research status,some suggestions are presented for future research for domestic researchers on the coincidence summing effect correction.First,the efficiency must be accurately established for the geometrical conditions of the measurement.Second,the number of cascades in the algorithm must be taken into account owing to its influence on the results.Third,correction software with a user-friendly interface and database of accurate decay schemes should be developed.

Measurement of the four relevant radioxenon isotopes, namely 131mXe, 133mXe, 133Xe, and 135Xe, play a key role in underground nuclear explosion monitoring for ensuring compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). A β-γ coincidence system that employs a plastic scintillator detector and a HPGe detector was developed in Beijing Radionuclide Laboratory. The Minimum Detectable Activity (MDA) in a 24-h measurement of the system for 131mXe, 133mXe, 133Xe and 135Xe can achieve 1.8 mBq, 1.4 mBq, 3.4 mBq and 4.1 mBq, respectively.

Eleven years after the Fukushima accident, independent objective estimates of the atmospheric 137Cs release still suffer from discontinuities such as negative release terms, oscillations, and temporal gaps, leading to noticeable differences from the subjective estimate. This paper describes an objective method that handles these artifacts and promotes the continuity of releases at fine resolutions. The proposed method uses the joint estimation model to reduce the oscillations induced by the model-observation discrepancies, and employs total variation regularization to recover the missing releases caused by insufficient observations. Adaptive parameterization is used to correct negative values. The application of this method to the Fukushima accident produces a source term that accurately approximates continuous releases at a fine temporal resolution of 1 h, providing a better match with the recognized subjective source term than nine published estimates, with a Pearson's correlation coefficient of 0.923 and an index of agreement of 0.872. This source term agrees with the timing of on-site gamma dose rate peaks, significantly improving the air concentration and deposition simulations, with FAC10 values of 0.564 and 0.990, respectively. The estimation error varies smoothly in a limited range with different regularization parameters, enabling automatic parameterization and demonstrating the potential for operational inversions.

Measurement of the four radioxenon isotopes, namely 131mXe, 133mXe, 133Xe, and 135Xe, play a key role in underground nuclear test monitoring for ensuring compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). To improve detection sensitivity, a β-γ coincidence technique is commonly used. Due to the presence of the gas matrix, such as stable xenon, nitrogen, helium, the self-attenuation effects should be taken into account when measuring different types of sample. In order to improve the accuracy of the measurement, the detection efficiencies of X-rays and γ-rays were derived by using a simulation gas calibration source with low density of sponge matrix. The detection efficiencies of β-particles and conversion electrons (CEs) were calibrated by measuring radioxenon sample. The self-attenuation correction factors of X-rays and γ-rays were determined by Geant4 simulation method. The self-attenuation correction factors of β-particles and CEs were provided by measuring the radioxenon samples with different volumes of xenon, nitrogen and helium.

Radioxenon monitoring is one of the important methods used by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) to detect a clandestine nuclear weapon test. Many radioxenon detection systems have been developed in the past few decades. The disadvantages such as bad energy resolution, memory effect, and large size influence the performance of these systems. This work introduces a new detection system that utilizes a PIPSCell and two CZT-Arrays for radioxenon monitoring. Signals from ten detectors are processed and coincidence events are identified via the electronics based on time-stamped list mode. This compact system has good radiation detection resolution at room temperature and high detection sensitivity for both electron and gamma-ray. Preliminary 137Cs and 131mXe are used to calibrate the energy and efficiency of the system. Combined with the simulation results the minimum detection activity of four radioxenon were assessed.

11 years after the Fukushima accident, the independent objective estimates of the atmospheric 137Cs release still suffer from discontinuities such as negative release terms, oscillations, and temporal gaps, leading to noticeable differences from the subjective estimate. In this paper, we propose an objective method that provides a continuous source term by sequentially combining the joint estimation model and total variation regularization. The joint estimation model corrects the model–observation discrepancies and reduces oscillations, while the total variation regularization imposes a piecewise-constant prior and recovers information about the release that may be missing as a result of insufficient observations. An adaptive parameterization is proposed to correct negative values. Validation against the Fukushima accident demonstrates that the retrieved source term is continuous, better agreeing with the recognized subjective source term than nine published estimates both qualitatively and quantitatively. It agrees with the timing of on-site gamma dose rate peaks, significantly improves the air concentration simulations, and reproduces the fine details to the south of the nuclear power plant and in the Chiba area. The estimation error of the proposed method varies smoothly in a limited range with different regularization parameters, enabling automatic parameterization and demonstrating the potential for operational inversions.

Temporal absences in observation records lead to release losses during the source term inversions of atmospheric radionuclide emissions. Consequently, objectively-estimated source terms for the Fukushima accident contain fewer release details and present large discrepancies when compared with the expert-judged one. This paper describes an objective method that can adaptively recover the missing releases caused by the temporal absences of observations. The proposed method assumes that the accident releases of radionuclides are piecewise-constant and comprise both peaks and constant releases. The missing releases are adaptively recovered as either peaks or constant releases by minimizing the total variation of the estimated source term. The proposed method is applied to the Fukushima accident and evaluated against regional airborne and deposited 137Cs observations. The results demonstrate that this method effectively recovers the missing releases, producing a source term that matches the timing of both on-site gamma dose rate peaks and accident events. The retrieved source term improves the simulation of air concentrations and reproduces most of the deposition patterns. This is the first time that an objective method has independently reproduced the details in the expert-judged one for the Fukushima accident.

The source term of atmospheric radionuclide releases is essential for the hazardous consequence assessment and emergency response. However, the artificial release oscillations in the source term estimate remain a fundamental challenge and may deliver misleading information, because of the unavoidable model biases and observation uncertainties. We propose a new method that removes oscillations while recovering the release details. This method explicitly corrects the model biases using the joint correction model and compensates the observation uncertainties through non-smooth competing priors that involve two rival functions. The new priors better model the unsteady feature of the radionuclide releases and distinguish the true releases from oscillations, enabling release-preserving oscillation removal. We extend the projected alternating minimization algorithm for an efficient solution. The method achieves oscillation-free and nearly perfect profiles for real releases of the Perfluoro-Methyl-Cyclo-Hexane on continental and regional scales, and the radionuclide 41Ar on a local scale, outperforming state-of-the-art and very recent methods. The sensitivities to model inputs and key parameters are also investigated. Robust performance is exhibited under emissions of both radioactive and non-radioactive substances, different meteorological inputs and numbers of observations, paving the way for identifying dynamic atmospheric radionuclide releases at multiple scales, especially when the release status is unknown.

Four CTBT relevant radioxenon isotopes, namely (131)mXe, (133)mXe, Xe-133 and Xe-135, play a key role for underground nuclear test monitoring. In order to improve the detection sensitivity of radioxenon, a plastic scintillator detector, which was used as the detector as well as the gas sample cell, was developed. Then the performances of the plastic scintillator detector were tested. The hermetic seal was quite good with the leakage rate less than 1x10(-4)Pa.L/s. The energy resolution of 129.4 keV conversion electron associated with (131)mXe was determined to be 27%. A significantly high detection efficiency of-particle was achieved. The detection efficiencies of 346.4 keV -particle for Xe-133 and 129.4 keV conversion electron for (131)mXe are 0.966 +/- 0.029 and 0.988 +/- 0.005 respectively. The memory effect was found to be less than 3%. The plastic scintillator detector provides adequate foundation of beta-gamma(HPGe) coincidence measurement method research of high resolution and high sensitivity.

研究碳分子筛的大气氩氪氙富集、浓缩与纯化行为,并结合膜分离技术,建立了一套大气中氩、氪、氙综合取样技术方案和取样流程,实现了氩、氪、氙样品的高效获取.结果 表明,13 h氙实际获取量5.2 mL,氪获取量15.2 mL,氩获取量392 mL.

The dispersion timeline and the specific ratio characterization of airborne radionuclides released from the Fukushima Daiichi Nuclear Power Plant accident were investigated based on an analysis of the monitoring data obtained from regional stations and radionuclide stations of the International Monitoring System for the Comprehensive Nuclear-Test-Ban Treaty. The comprehensive temporal sequence of airborne radionuclide arrival time at different sites was given, including xenon, iodine, and cesium isotopes, which could be used to validate and evaluate atmospheric transport modeling. Based on the decay time estimation method, the release time and process of radionuclides were calculated and analyzed through activity ratios of I-133 to I-131, Cs-136 to Cs-137, and Cs-134 to Cs-137. It indicated that radioiodine isotopes leaked from the reactors in the early stage after the 2011 Great East Japan Earthquake occurred, and there were two sources which leaked radiocesium, one is units 1, 2, and 3 of the Fukushima Daiichi NPP and the other is the spent fuel pools with a high possibility. Generally, this study provides some valuable findings and information for further evaluation of the accident and relevant research work.