BackgroundAppropriate fast detection method for radionuclides is necessary for customs radioactive security inspection with high flow rates and low counting rate levels. Compared with the traditional uncertainty analysis method, the Bayesian method and the Sequential Probability Ratio Test can fully utilize all the information of measured physical quantities and reduce the required sample size.PurposeThis study aims to develop a new method to solve the problem of the fast and accurate detection of radionuclides at low radioactive counting rate scenarios.MethodsA new Sequential Bayesian fast detection method for radionuclides was proposed on the basis of binary hypothesis H0 (no radionuclides) and H1 (radionuclides). Based on the principle that the time interval between adjacent two rays was exponential distributed, the decision was caculated by collecting a series of ray time samples in chronological sequence, and decisions were made by comparing the decision function with the preset upper and lower thresholds. Finally, experimental verifications were conducted on the feasibility, detection performance, and universality of the method by placing a set of standard point sources at different distances from the front of a LaBr3(Ce) detection system in both low and natural radiation background environments. The effects of the key parameters of the method on the detection performance were investigated.ResultsUnder the absence of radionuclides in two type of background radiation environments, the average detection time for background radiation by this method is 24.08 s and 10.54 s, with an average detection sample size of 1 427 and 1 742, respectively. Under the presence of radionuclides in two type of background radiation environments, the lower limits of detection sensitivity of experimental measurements are 8.2% and 6.1%, respectively, the corresponding average detection times were only 8.59 s and 6.61 s respectively, and the experimental measurement false negative rates were all zero.ConclusionsResults of this study verify that above proposed method is very suitable for fast detection of low-level radionuclides.

BackgroundElectroporation technology can be used in biomedicine, food safety, sewage treatment and other fields. The pulse waveform is an important parameter affecting electroporation efficiency.PurposeThis study aims to propose a distributed arbitrary waveform high-voltage pulse generator composed of multiple standard pulse power modules to meet the needs of controllable electroporation.MethodsFirstly, based on full bridge inverter structure, the framework of the distributed generator with bipolar all solid state Marx topology was designed, and the basic working principle of the main circuit of standard module was elaborated. Then, the power and load parameters were simulated and analyzed using Simulink module of MATLAB software. Based on the simulation results, a prototype generator composed of two standard modules in series was built, and the resistance load test was carried out. Finally, under the condition of the same pulse amplitude and pulse energy, the electroporation experiment of microalgae was carried out to verify the correctness and feasibility of high-voltage pulse generator.ResultsThe generator can output arbitrary pulse waveform of ±8 kV with 33 electrical levels. Under the condition of pulse amplitude 8 kV and pulse energy 0.4 J, the electroporation efficiencies of positive square wave and exponential attenuation wave are 65.25% and 46.15%, respectively.ConclusionsThe applicability of the generator proposed in this study is demonstrated in the controllable electroporation experiment, and the electroporation efficiency of square wave with constant amplitude and energy is higher than that of exponential attenuation wave.

BackgroundIn order to apply in different scenarios of silicon photomultiplier (SiPM) coupled scintillator detector, preamplifiers need to fulfill different requirements.PurposeThis study aims to design high-bandwidth, low-noise preamplifiers to adapt for different output modes of SiPM-coupled scintillator detector.MethodsBased on OPA855 chip and consideration of bandwidth and noise, a transimpedance amplifier (TIA) and a voltage feedback amplifier (VFB) were designed. The amplifier circuits were simulated and analyzed using PSpice for TI software to obtain circuit parameters. Then, the signal response and noise baseline level were measured and analyzed by experimental test using 241Am radioactive source and a sSiPM-coupled Cerium-doped Gadolinium Aluminum Gallium Garnet (GAGG(Ce)) detector.ResultsExperimental results show that these preamplifiers have good gain stability, high-bandwidth and low-noise. TIA's bandwidth is 101 MHz, lower than VFB's 381 MHz, but its baseline noise level (σnoise≈448.32 μV) is better than that of the VFB's ( σnoise≈680.96 μV).ConclusionsFor GAGG(Ce) detector ,both VFB and TIA meet the bandwidth design requirements of 2 ns for fast output pulse and 20 ns for standard output pulse, respectively. Limited by the inherent noise of circuits and the input capacitance of SiPM,TIA is suitable for energy measurements and small-area SiPM applications, while VFB is more suitable for time measurements and large-area SiPM arrays.

BackgroundIn order to ensure the accuracy of the dose received by the patient in radiotherapy, it is usually necessary to verify the plan before treatment, and the water tank is widely used to achieve this purpose. However, the existing dose validation tanks can only be used for beam therapy terminals with horizontal, vertical and 45° angles, which cannot meet the multi-angle dose validation requirements of the advanced rotary Gantry beamline treatment rooms.PurposeThis study aims to develop a three-dimensional (3D) water tank for multi-angle beam dose verification, so as to meet the beam detection requirements of multi-direction beam irradiation of gantry beam line.MethodsThe water tank box was constructed from Polymethyl Methacrylate (PMMA) and driven by the motor to rotate around the isocenter. Solidworks Simulation software package was employed to simulate the structure of the water tank, and the motion accuracy of the 3D motion mechanism was evaluated. The lateral profile dose distribution of the beam at different depths in the water was measured by a multi-strip ionization chamber (MSIC), and a 3D dose distribution of the pencil beam was obtained by stacking the profile dose distribution measured at different depths. The measurement results were compared with data obtained from commercial PTW water tank.ResultsEvaluation results show that, the maximum position error of the probe is 0.132 mm when the probe is moving in the depth direction, the maximum position error of the probe is 0.24 mm in the Y and Z directions for the probe position adjustment, and the dose measurement deviation is 0.5%±1.18%.ConclusionsThe water tank proposed in this study can quickly and accurately provide the 3D dose distribution of a pencil beam, hence, provide basic data for treatment planning systems and improve the efficiency of regular quality assurance practice. The whole measuring device can be rotated around the isocenter of the treatment head, meeting the beam detection requirements of multi-directional irradiation in the Gantry treatment rooms.

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.

BackgroundMultisphere neutron spectrometers are pivotal in accurately measuring neutron flux across various fields. The inherent complexities and non-linearities in their calculation processes, such as correlated variables, make traditional uncertainty analysis methods based on theoretical models and empirical formulas (e.g., the GUM (Guide to the Uncertainty in Measurement) method) unsuitable.PurposeThis study aims to demonstrate the application of the Monte Carlo (MC) method as an effective tool for evaluating measurement uncertainty in multi-sphere spectrometers, addressing the challenges posed by complex systems and non-linear problems.MethodsFirst of all, the MC method was employed to conduct probability density sampling of input variables to obtain the probability density distribution of the output variables. Detailed statistical characterization of the calculation results was allowed to provide a more comprehensive understanding compared to conventional methods. Then, numerous simulations were performed to take into account of variability and uncertainty in the input parameters, hence the robustness of the analysis was enhanced. Consequently, this technique overcome the limitations of traditional deterministic approaches, offering more reliable and nuanced insights into the system's behavior. Finally, experiments were carried out using multisphere neutron spectrometers and neutron field standard device (including 4 neutron sources), and the measurement results of neutron flux spectrum under 30 cm iron ball shielding were evaluated using above-mentioned method.ResultsThe spectrum unfolding results obtained by this method have a total uncertainty of 5% in the energy group of interest after being passed by the spectrum unscrambling program.ConclusionsThe application of the MC method offers a robust framework for the assessment of measurement uncertainties in multi-sphere neutron spectrometers. This study not only enhances the accuracy and reliability of spectrometer measurements, but also contributes to the broader field of neutron measurement techniques by providing a reference for the evaluation of complex systems.

BackgroundGaussian pulses have good time and frequency domain characteristics, and perform well in terms of signal-to-noise ratio, ballistic loss, and other aspects of the synthesis. When performing Gaussian pulse shaping, errors introduced by hardware limitations may lead to differences in shaping results. Compared to infinite impulse response (IIR) filters, finite impulse response (FIR) filters have the advantage of being less affected by errors and more stable.PurposeThis study aims to propose a FIR filter-based Gaussian pulse shaping algorithm using impulse response functions, and realize a FPGA-based hardware implementation of this algorithm to evaluate the impact of hardware limitations on it.MethodsFirst of all, the discrete impulse response of Gaussian pulse shaping (GPS) was derived by means of impulse response invariant transformation, and shaped pulse waveforms under different quantization accuracies and truncation intervals were obtained using a computer simulation, so did that under Gaussian pulse shaping with or without additional truncation were assessed. Then, X-ray fluorescence signals emitted by Mn sample was acquired using fast silicon drift detector (FAST-SDD) to assess shaping performance on the spectrum, and processed by a digital multichannel analyzer utilizing FIR GPS algorithm implemented in a field programmable gate array (FPGA) processing board. Finally, peak area and energy resolution of the spectrum were used to compare performances of GPS under different quantization accuracies and truncation intervals, as well as performances of three methods of trapezoidal pulse shaping, Gaussian pulse shaping with additional truncation method and normal GPS.Results & ConclusionsFor comparisons of quantization accuracy, when the quantization accuracy is greater than 4 bits, the shaping performance of GPS remains consistently stable within the peaking time ranging from 120 ns to 1 140 ns when the quantization accuracy is greater than 4 bits. Otherwise, the influence of low quantization accuracy on GPS is minimized ranging from 420 ns to 780 ns. For inter-method comparisons, GPS with or without additional truncation outperform trapezoidal pulse shaping. The truncated GPS algorithm has better energy resolution and saves more hardware resources, whilest the normal GPS algorithm owns better pulse pile-up rejection capability for the same peaking time.

BackgroundThe gas ionization chamber is a kind of intensity monitoring detector widely used in Synchrotron Radiation Facility. Lytle detector is often used to measure the fluorescence signal from the element of interest in the fluorescent mode XAFS (X-ray absorption fine structure), it is one of the important fluorescence detectors for the X-ray absorption spectrum study and used in XAFS beamline station of Shanghai Synchrotron Radiation Facility (SSRF). However, this type detector is predominantly manufactured by foreign company (The EXAFS Company).PurposeThis study aims to develop a domestic fluorescent gas detector according to the operating conditions and technical requirements of fluorescent mode XAFS.MethodsFirstly, a filter and a slit assembly were designed and optimized with Geant4 toolkit. Subsequently, a multilayer grid ionization chamber for fluorescence detection was designed, and the supporting electronics circuit with both high voltage and amplification gain functions was designed. Secondly, all components were manufactured and assembled into a complete detector, and the digital noise, response time, response intensity, and linearity of self-developed detector were tested at BL11B beamline of SSRF. Finally, the actual measured performance of self-developed detector was tested and compared with Lytle detector at BL11B beamline.ResultsThe test results indicate that the digital noise level is approximately ~3.2×10-9 V, which is superior to the (9~10)×10-9 V observed in the Lytle detector. Additionally, the response time is less than 2.1 ms, significantly outperforming the Lytle detector's response time of approximately 150 ms. The linearity of the detector's response also exceeds 0.999 6.ConclusionsThe self-developed detector with shorter response times and better performance than Lytle detector has been achieved, and the localization replacement of the Lytle type detector is realized. Meanwhile, it has been used in the fluorescent mode XAFS of BL11B beamline at SSRF.

BackgroundIn order to enhance the detection sensitivity of HPGe detectors for measuring the low-level activity of radionuclides, samples are usually measured as close to the detector as possible to improve the detection efficiency, which inevitably leads to serious coincidence-summing effects in return and affects the accuracy of measured activity.PurposeThis study aims to conduct efficiency simulation and coincidence-summing correction for HPGe detectors.MethodsFirst of all, the peak efficiency of the HPGe detector was simulated by Geant4 and the internal geometry of the HPGe detector was optimized by comparing the simulated results with the experimental results of the mixed standard calibration source. Then, the total efficiency of the detector with various dead layer thickness was calibrated and the coincidence-summing correction factors were calculated. Finally, "Proficiency Test Exercise (PTE) 2021" conducted by the Provisional Technical Secretariat (PTS) of Comprehensive Nuclear Test Ban Treaty (CTBT) was applied to the correction of the measured activity.ResultsMeasurement results show that the relative deviation between the corrected activity and the reference result is less than 3%.ConclusionsResults of this study demonstrate that the efficiency simulation and coincidence-summing correction for HPGe detector solves problems of limited calibration point source and high experimental cost, lays a foundation for measuring activities of nuclides in the sample accurately.

BackgroundDeveloping electronic devices, such as metal oxide semiconductor field effect transistor (MOSFET) amplifiers with high radiation resistance, is crucial for robots working in nuclear environments.PurposeThis study aims to test the irradiation resistance performance of commercial MOSFET amplifiers and reveal the corresponding irradiation failure mechanism.MethodsAn in-situ gamma rays irradiation experiment platform was employed to conduct irradiation test on three trench MOSFET amplifiers using a 60Co source. Response to different doses, and the electrical properties of these MOSFET amplifiers were investigated before and after irradiation. The failure analysis methods including electrical characteristics tests, thermal emission microscopy (EMMI) for failure location determination, focused ion beam (FIB) sample preparation, scanning electron microscope (SEM), and transmission electron microscope (TEM) characterization were employed to reveal the irradiation failure mechanism.ResultsExperimental results showed that the three MOSFET amplifiers failed after irradiation by absorbed doses of 982.6 Gy, 986.2 Gy, and 1 082.4 Gy, respectively. The drain-source breakdown voltage BVDSS of the MOSFET decreases from 110.5 V to 0.96 V, while the gate-source drive current IGSS increases from 2.9 nA to 81.3 mA, as well as the threshold voltage VGS(th) is not be detected due to the short circuit.ConclusionsWhen the MOSFET amplifiers are irradiated in a charged operating state, the accumulation of captured charges in the gate oxide will lead to a decrease in the threshold voltage and breakdown voltage. Electron-hole pairs generated by high-energy and high-dose gamma-ray irradiation may continue to accumulate under the action of the circuit electric field, resulting in local high electric fields and high heat areas. The superposition of these high electric fields and high heat areas will cause the source aluminum metal to melt and ablate, causing a short circuit between the gate and the source.

BackgroundRadioactivity measurement is widely used in various fields of nuclear technology application. The measurement uncertainty, confidence interval and detection limit are important parameters in radioactive measurement. Different calculation methods may get different results, and the calculation results directly affect some important and relevant decisions.PurposeThis study aims at the calculation method of parameters in α particle radioactivity measurement that is used properly.MethodsBoth the partial derivative method and Monte Carlo method were applied to determinate the important parameters of α particle radioactivity measurement in this study. Firstly, based on the measurement of α activity concentration in gas using Passivated Implanted Planar Silicon (PIPS) detector, the sources of uncertainty for the measurement results were analyzed in details. Then, measurement uncertainty, confidence limits, decision threshold and detection limit of α particle activity concentration under different input modes were derived and calculated by partial derivative and Monte Carlo methods, singly and jointly. Finally, calculation results were compared analyzed.ResultsThe results show that when the input uncertainty is higher than 10%, the relative deviation between confidence interval and uncertainty results obtained by the two calculation methods is greater than 15%. When the relative uncertainty of the input is small, the detection limit is about 2 times of the decision threshold.ConclusionsThe partial derivative method is widely used without consideration of the probability distribution of the input, hence not suitable for complex and special input models. Under this circumstances, Monte Carlo method can be used to obtain more reliable calculation results. The two approaches can be applied jointly in complementary ways.

BackgroundDue to high energy resolution and position sensitivity features, the multi-electrode high purity germanium (M-HPGe) detector is widely applied in rare event physics for events extraction.PurposeThis study aims to make use of pulse shape in M-HPGe detector as a useful reference to optimize the performance of gamma spectrometry, rare events detection and signal/background discrimination of M-HPGe detector in other scenarios.MethodsThe pulse shape of inductive charge at different readout electrodes in M-HPGe detector was simulated by joint calling process of Monte Carlo simulation process and single point position energy deposition pulse waveform simulation. Then, the pulse shape in M-HPGe detector was estimated through the distribution of the internal electric field, the weighting potential inside the detector, the carrier track and the inductive charge at the readout electrode.ResultsSimulation results of pulse shape in M-HPGe detector show that the collector electrodes along the electrodes distribution induces significantly different inductive signals, and weak mirror signals are induced by the adjacent electrodes. This indicates that the M-HPGe detector has position resolution feature along the electrodes distribution.ConclusionsThis method can be used to support the research on the physical mechanism of the gamma track reconstruction discrimination method, and it can also simulate and evaluate the application effect of the track reconstruction discrimination method.

BackgroundEtched track dosimeters (ETDs) based on CR-39 foils are the most frequently used passive detectors for neutron personal dosimetry at various nuclear facilities. That applying a pre-treatment in carbon dioxide (hereafter, CO2 pre-treatment) can improve the CR-39 detection sensitivity and enlarge the tracks is extremely valuable and warrants further investigation.PurposeThis study aims to investigate the effect of CO2 pre-treatment on the sensitivity and the track size distributions of CR-39 detectors, and to obtain an optimal CO2 pre-treatment condition.MethodsA parametric study was conducted to evaluate the effect of CO2 pre-treatments at different pressures and durations on CR-39 detectors. The detectors were firstly irradiated by a standard 252Cf neutron source, delivering a personal dose equivalent Hp(10) of 2 mSv. Then, the detectors were subjected to carbon dioxide treatment prior to undergoing chemical etching for durations ranging from 6 h to 168 h at partial pressures varying between 0.1 MPa to 1.6 MPa. Finally, the correlation between detector sensitivity and pre-treatment condition was obtained by analyzing the number of registered tracks and track size distribution under each pre-treatment condition.ResultsThe obtained results indicate that the CO2 pre-treatment significantly improves sensitivity and maximum track size, with the sensitivity increasing by up to 870% and the maximum track size expanding from 20 μm to 40 μm. The sensitivity increases linearly with pre-treatment pressures, and the saturation point of the maximum track size appears around 40 μm. As the time and pressure continue to increase, the neutron spectrometry information contained in the track size distributions will be erased, the optimal sensitivity for CR-39 to retain the spectral information in the track size distributions is 6.25 tracks·mm-2·mSv-1.ConclusionsThis study is of significance for improving the sensitivity of CR-39 detectors in neutron dosimetry and selecting CO2 pre-treatment conditions, providing a processing method to enhance the track readability whilst preserving the spectral information in the track distributions for practical applications of CR-39 detectors in neutron dosimetry and spectrometry.

BackgroundThe high frame rate area detector is the core detector for the major imaging-based experimental stations at the Shanghai HIgh repetitioN rate xfel and Extreme light facility (SHINE), and its data throughput is expected to reach more than 20 GB·s-1. For the real-time receiving and processing of tens of GB·s-1 raw data, traditional single-machine systems are difficult to cope with.PurposeThis study aims to propose a multi-node distributed data acquisition and processing software architecture for high frame rate area detector at imaging-based experimental stations of SHINE.MethodsFirstly, the performance of different network libraries was investigated, and the synchronous transmission method combined with CPU thread binding was found to have the best single-thread data receiving performance. Then, a parallel event building method was introduced by simultaneously dispatching and combing different module data across multiple nodes based on Bunch ID. Furthermore, the data calibration and the bitshuffle/LZ4 compression algorithm were implemented and tested.ResultsTest results show that the highest single-thread data receiving rate is achieved at nearly 3 GB·s-1, a parallel event building data rate of approximately 23.5 GB·s-1 is achieved by using 4 server nodes, and the realized compression ratio is about 5.7.ConclusionsThe feasibility of the multi-node distributed parallel data acquisition method for high frame rate area detector is verified in this study, providing a foundation for the subsequent development of high-throughput data acquisition software for area detectors.

Background222Rn/220Rn and their daughters are widely present in the atmosphere and indoor environment. The presence of high-concentration 220Rn can affect the accuracy of 222Rn concentration measurements.PurposeThis study aims to measure radon concentration more accurately by investigating the variation in the response coefficients of the AlphaGUARD PQ2000 radon monitor to 220Rn under thoron gas concentrations with different wind speeds and directions within a standard radon chamber.MethodsThe single-scintillation proportional counter flow gas static method was employed to determine the thoron concentration in this study. Firstly, a self-made and stable high emissivity solid 220Rn source at the University of South China was applied to the generation of 220Rn gas in the chamber, a temperature and humidity control system was adopted to regulate the inside temperature and humidity of 220Rn whilst the wind speed was controlled by changing the operating frequency of the variable frequency fan. Then, the readings of the AlphaGUARD PQ2000 were observed at various wind speeds and directions under controlled temperature and humidity conditions. Subsequently, the response coefficients of the AlphaGUARD PQ2000 to thoron in diffusion mode were calculated according the observed results.ResultsWhen the wind speed increases from 0.05 m·s-1 to 3.50 m·s-1, the response coefficient of AlphaGUARD PQ2000 to 220Rn increases from 0.044 to 0.126. When there is no wind, the response coefficient is 0.049. When the wind speed is fixed at 0.71 m·s-1 and the angle between the wind direction and AlphaGUARD PQ2000 diffusion window changes from 0° to 180°, the response coefficient decreases from 0.083 to 0.051. When the wind speed is fixed at 1.43 m·s-1 and the angle between the wind direction and AlphaGUARD PQ2000 diffusion window changed from 0° to 180°, the response coefficient is reduced from 0.115 to 0.081.ConclusionsThe response coefficients obtained in this study can provide a reference for correcting the interference of 220Rn in the measurement results of the diffusion mode of the AlphaGUARD PQ2000 radon detector.

BackgroundNuclear sites require monitoring of artificial radioactive aerosols, but existing instruments often encounter the problem of "measurement uncertainty (radon progeny interference)" in the measurement of artificial radioactive aerosols, requiring effective calibration of radon daughter interference levels.PurposeThis study aims to accurately calibrate the radon progeny measurement instruments and effectively calibratt the radon progeny aerosol interference levels for artificial radioactive aerosol monitoring instruments.MethodsBased on the behavior patterns of aerosol particles and radon along with its progeny, a small volume radon progeny aerosol control device was developed, which was composed of aerosol dilution loop, radon progeny regulation loop, and controller with programmable logic controller (PLC) control system. In the aerosol dilution loop, varying concentrations of carrier aerosols was achieved by utilizing a circulating pump in conjunction with a aerosol generator. In the radon progeny regulation loop, different levels of radon sources were employed to achieve regulation of radon activity concentration. Radon progeny aerosol with stable radon progeny state parameters was achieved by adjusting the radon concentration, aerosol concentration and air exchange rate, and the performance of this device was verified by experiments.ResultsExperimental results show that the stable regulation range of equilibrium equivalent concentration (EEC) is 3.3×102~9.4×103 Bq?m-3, stable regulation range of equilibrium factor: 0.12~0.58, stable regulation range of unbound fraction: 1.4%~62.7%. The variation range of EEC within 4 h is within 10%, and the relative standard deviation of the uniformity experiment is less than 7%.ConclusionsThe stable regulation range of the radon progeny state parameters of the small volume radon progeny aerosol control device proposed in this study is wide, and the uniformity and stability of the radon progeny are good. It can be used to effectively simulate the field measurement environment, achieving the development purpose of this device.