Vol.35,

Cosmic-ray muons are highly penetrating background-radiation particles found in natural environments. In this study, we develop and test a plastic scintillator muon detector based on machine-learning algorithms. The detector underwent muon position-resolution tests at the Institute of Modern Physics in Lanzhou using a multiwire drift chamber (MWDC) experimental platform. In the simulation, the same structural and performance parameters were maintained to ensure the reliability of the simulation results. The Gaussian process regression (GPR) algorithm was used as the position-reconstruction algorithm owing to its optimal performance. The results of the Time Difference of Arrival algorithm were incorporated as one of the features of the GPR model to reconstruct the muon hit positions. The accuracy of the position reconstruction was evaluated by comparing the experimental results with Geant4 simulation results. In the simulation, large-area plastic scintillator detectors achieved a position resolution better than 20 mm. In the experimental-platform tests, the position resolutions of the test detectors were 27.9 mm. We also analyzed factors affecting the position resolution, including the critical angle of the total internal reflection of the photomultiplier tubes and distribution of muons in the MWDC. Simulations were performed to image both large objects and objects with different atomic numbers. The results showed that the system could image high- and low-Z materials in the constructed model and distinguish objects with significant density differences. This study demonstrates the feasibility of the proposed system, thereby providing a new detector system for muon-imaging applications.

225

Identifying sensitive areas in integrated circuits (ICs) susceptible to single-event effects (SEE) is crucial for improving radiation hardness. This study presents an online multi-track location (OML) framework to enhance the high-resolution online trajectory detection for the Hi’Beam-SEE system, which aims to localize SEE-sensitive positions on the IC at the micrometer scale and in real time. We employed a reparameterization method to accelerate the inference speed, merging the branches of the backbone of the location in the deployment scenario. Additionally, we designed an irregular convolution kernel, an attention mechanism, and a fused loss function to improve the positioning accuracy. OML demonstrates exceptional real-time processing capabilities, achieving a positioning accuracy (PA) of 1.83 μm in processing data generated by the Hi’Beam-SEE system at 163 frames per second(fps) per GPU.

146

Nuclear energy is a vital source of clean energy that will continue to play an essential role in global energy production for future generations. Nuclear fuel rods are core components of nuclear power plants, and their safe utilization is paramount. Due to its inherent high radioactivity, indirect neutron radiography (INR) is currently the only viable technology for irradiated nuclear fuel rods in the field of energy production. This study explores the experimental technique of indirect neutron computed tomography (INCT) for radioactive samples. This project includes the development of indium and dysprosium conversion screens of different thicknesses and conducts resolution tests to assess their performance. Moreover, a pressurized water reactor (PWR) dummy nuclear fuel rods have been fabricated by self-developing substitute materials for cores and outsourcing of mechanical processing. Experimental research on the INR is performed using the developed dummy nuclear fuel rods. The sparse reconstruction technique is used to reconstruct the INR results of 120 pairs of dummy nuclear fuel rods at different angles, achieving a resolution of 0.8 mm for defect detection using INCT.

225

Accurate real-time simulations of nuclear-reactor circuit systems are particularly important for system safety analysis and design. To effectively improve computational efficiency without reducing accuracy, this study establishes a thermal-hydraulics reduced-order model (ROM) for nuclear-reactor circuit systems. The full-order circuit system calculation model is first established and verified and then used to calculate the thermal-hydraulic properties of the circuit system under different states as snapshots. The proper orthogonal decomposition method is used to extract the basis functions from snapshots, and the ROM is constructed using the least-squares method, effectively reducing the difficulty in constructing the ROM. A comparison between the full-order simulation and ROM prediction results of the AP1000 circuit system shows that the proposed ROM can improve computational efficiency by 1500 times while achieving a maximum relative error of 0.223%. This research develops a new direction and perspective for the digital-twin modeling of nuclear-reactor system circuits.

198

A multi-group cross-section library is fundamental for deterministic lattice physics calculations. Most existing multi-group cross-section libraries are customized for particular computer codes, as well as for particular types of nuclear reactors. This paper presents an HDF5-format multi-group cross-section library named XPZLIB. XPZLIB was produced using a self-developed XPZR module integrated into the NJOY2016 code, and an in-house PyNjoy2022 system was developed for auto-processing. XPZLIB contains detailed data content and well-organized data structures that are user- and developer-friendly. Three typical XPZLIBs with different numbers of energy groups, nuclides, and depletion reaction types were released via the Tsinghua cloud website. Furthermore, the applicability of the released XPZLIBs was investigated using HTGR and PWR lattice calculations, which can provide guidance for applying XPZLIB under different scenarios.

152

Predicting the transition-temperature shift (TTS) induced by neutron irradiation in reactor pressure-vessel (RPV) steels is important for the evaluation and extension of nuclear power-plant lifetimes. Current prediction models may fail to properly describe the embrittlement trend curves of Chinese domestic RPV steels with relatively low Cu content. Based on the screened surveillance data of Chinese domestic and similar international RPV steels, we have developed a new fluence-dependent model for predicting the irradiation-embrittlement trend. The fast neutron fluence (E> 1 MeV) exhibited the highest correlation coefficient with the measured TTS data; thus, it is a crucial parameter in the prediction model. The chemical composition has little relevance to the TTS residual calculated by the fluence-dependent model. The results show that the newly developed model with a simple power-law functional form of the neutron fluence is suitable for predicting the irradiation-embrittlement trend of Chinese domestic RPVs, regardless of the effect of the chemical composition.

136

The evolution of the microstructure and tensile rupture mechanism of laser welds in UNS N10003 alloy exposed to 700 °C are investigated. Fine M₆C carbides precipitate around the primary eutectic M₆C-γ carbides in the fusion zone after 100 h of exposure. During long-term thermal exposure, the size of the fine M₆C carbides increased. The eutectic M₆C-γ carbides in the as-welded fusion zone transformed into spherical M₆C carbides as the exposure time extends to 10000 h. Additionally, the spherical M₆C particles exhibit size coarsening with increasing exposure time. The tensile properties of the welded joints are not adversely affected by the evolution of eutectic M₆C-γ carbides and the coarsening of M₆C carbides.

210

We modified Zr/Ce-UiO-66-NH₂ using dual bimetallization and amination strategies to efficiently extract uranium from water resources. XRD, FTIR, and XPS indicated the successful alteration of material amination. Moreover, the metal Zr was partially replaced by Ce in Zr-oxygen atom clusters in Zr/Ce-UiO-66-NH₂. It possessed commendable structural stability in acidic and alkaline solutions. Irrespective of whether it was submerged in a 6 M strong acid or in a 0.5 M strong base solution, the structural integrity of Zr/Ce-UiO-66-NH₂ remained unaffected. Batch experiments at pH = 6.0 revealed that uranium adsorption by Zr/Ce-UiO-66-NH₂ reached 376.8 mg·g^-1 and 611.33 mg·g^-1 at 298 K and 328 K, respectively. These values are much better than those obtained using bimetallic-modified Zr/Ce-UiO-66 or amine-functionalized UiO-66-NH₂. After five consecutive sorption and desorption cycles, the material retained a uranium removal rate of more than 80%, proving its excellent regenerative properties. Kinetic modeling of U(VI) adsorption on Zr/Ce-UiO-66-NH₂ implied that chemisorption dominated the rapid uranium sorption rate. We propose potential adsorption mechanisms involving three interactions: inner-sphere surface complexation, chemisorption, and electrostatic interactions. This study shows that the dual strategies of bimetallization and amination can effectively enhance U(VI) extraction from water. This approach has potential applications for the structural design of uranium adsorbents.

154

Machine learning algorithms are considered as effective methods for improving the effectiveness of neutron-gamma (n-γ) discrimination. This study proposed an intelligent discrimination method that combined a Gaussian mixture model (GMM) with the K-nearest neighbor (KNN) algorithm, referred to as GMM-KNN. First, the unlabeled training and test data were categorized into three energy ranges: 0–25 keV, 25–100 keV, and 100–2100 keV. Second, GMM-KNN achieved small-batch clustering in three energy intervals with only the tail integral Q_tail and total integral Q_total as the pulse features. Subsequently, we selected the pulses with a probability greater than 99% from the GMM clustering results to construct the training set. Finally, we improved the KNN algorithm such that GMM-KNN realized the classification and regression algorithms through the LabVIEW language. The outputs of GMM-KNN were the category or regression predictions. The proposed GMM-KNN constructed the training set using unlabeled real pulse data and realized n-γ discrimination of ²⁴¹Am^-Be pulses using the LabVIEW program. The experimental results demonstrated the high robustness and flexibility of GMM-KNN. Even when using only 1/4 of the training set, the execution time of GMM-KNN was only 2021 ms, with a difference of only 0.13% compared with the results obtained on the full training set. Furthermore, GMM-KNN outperformed the charge comparison method in terms of accuracy, and correctly classified 5.52% of the ambiguous pulses. In addition, the GMM-KNN regressor achieved a higher figure of merit (FOM), with FOM values of 0.877, 1.262, and 1.020, corresponding to the three energy ranges, with a 32.08% improvement in 0–25 keV. In conclusion, the GMM-KNN algorithm demonstrates accurate and readily deployable real-time n-γ discrimination performance, rendering it suitable for on-site analysis.

212

Stripping units take a key role in the neutral particle analyzer (NPA). A renovated gas-stripping unit was constructed for the newly designed E//B NPA. Using H₂ as the working gas, we measured the gas inlet pressure (P₀) and vacuum chamber pressure (P₃). The pressure distribution inside the gas-stripping room was calculated with Ansys Fluent, using the measured P₀ and P₃ as boundary conditions. The stripping efficiency of the stripping unit was then simulated utilizing the Geant4 Monte Carlo code for the H and D particles. The pressure P₀=40 Pa, which is one-sixth of what found in the previous design and corresponds to a thickness of 1.27×10¹⁷ atoms/cm², was obtained as the optimum working pressure for the upgraded stripping unit. An 50 kV electron cyclotron resonance (ECR) ion source platform was designed and constructed for E//B NPA calibration, and its performance has been measured. Using the ECR ion source platform, we measured the efficiency of the stripping unit through an inverse experiment with proton beams. We compared the current ratios of measurements with and without H₂ gas to Geant4 simulation results. We found adequate agreement between the overall trends of the experiment and the simulation. The significant deviation for incident energies below 20 keV may result from the scattering effects of low-energy protons, leading to reduced accuracy in single-scattering physics in Geant4 simulations. Applying the scattering corrections observed in the reverse experiments obtains more accurate stripping efficiencies for H and D atoms in the energy range of 20-200 keV, and the global efficiency with the maximum values of 95.0% for H atoms and 78.9% for D atoms at 200 keV.

138

In the current study, we examined every possible cluster–daughter combination in the heavy-particle decay of isotopes ^297–300119 and computed the decay half-lives using the modified generalized liquid drop model (MGLDM) with the preformation factor depending on the disintegration energy. The predicted half-life of every heavy cluster (Z_C ≥ 32)was within the experimentally observable limits. These results aligned with the predictions of Poenaru et al. [Phys. Rev. Lett. 107, 062503 (2011)] that superheavy nuclei (SHN) with Z> 110 will release heavy particles with a penetrability comparable to or greater than the α-decay. The half-lives predicted using the MGLDM for clusters ⁸⁹Rb, ⁹¹Rb, and ⁹²Rb from parents ²⁹⁷119, ²⁹⁹119, and ³⁰⁰119, respectively, agreed with the predictions of Poenaru et al. [Eur. Phys. J. A 54, 14 (2018)]. It was found that the isotopes of heavy clusters Kr, Rb, Sr, Pa, In, and Cd had half-lives comparable to the α half-life; and isotopes of clusters I, Xe, and Cs had the minimum half-life (10^–14 s). These observations revealed the role of the shell closure (Z = 82, N = 82, and N = 126) of the cluster and daughter nuclei in heavy-cluster radioactivity. We predicted that isotope ^297,299119 decayed by 4α decay chains and isotope ³⁰⁰119 decayed by 6α decay chains, while ²⁹⁸119 decayed by continuous α decay chains. The predicted half-lives and modes of decay of the nuclei in the decay chains of ^297–300119 agreed with the experimental data, proving the reliability of our calculations. The present study determined the most favorable heavy-cluster emissions from these nuclei and provided suitable projectile–target combinations for their synthesis.

174

Active target time projection chambers are state-of-the-art tools in the field of low-energy nuclear physics and are particularly suitable for experiments using low-intensity radioactive ion beams or gamma rays. The Fudan multi-purpose active target time projection chamber (fMeta-TPC) with 2048 channels was developed to study α-clustering nuclei. This study focused on the photonuclear reaction with a laser Compton scattering gamma source, particularly for the decay of the highly excited α cluster state. The design of fMeta-TPC is described in this paper. A comprehensive evaluation of its offline performance was conducted using an ultraviolet laser and ²⁴¹Am α source. The results showed that the intrinsic angular resolution of the detector was within 0.30 and the detector had an energy resolution of 6.85% for 3.0 MeV α particles. The gain uniformity of the detector was approximately 10% (RMS/Mean), as tested by the ⁵⁵Fe X-ray source.

156

The DarkSHINE experiment proposes a novel approach to single-electron-on-fixed-target exploration that focuses on the search for dark photons through their invisible decay into dark matter particles. Central to this initiative is an advanced tracking detector designed to achieve exceptional sensitivity in the detection of light dark matter candidates. This study evaluates the performance of several prototype AC-coupled low-gain avalanche diode (AC-LGAD) strip sensors specifically developed for the DarkSHINE tracking detector. The electrical properties of the sensors from two batches of wafers with different n⁺ doses are thoroughly evaluated. Spatial and temporal resolutions are measured using an infrared laser source. The spatial resolutions range from 6.5 to 8.2 μm and from 8.8 to 12.3 μm for the sensors from two distinct dose batches, each with a 100 μm pitch size. Furthermore, the sensors demonstrate time resolutions of 8.3 and 11.4 ps, underscoring the potential of AC-LGAD technology in enhancing the performance of the DarkSHINE tracking detector.

258

We report a comprehensive study on low-lying parity doublet states of ²²⁴Rn by mixing both quadrupole and octupole-shaped configurations in multireference covariant density functional theory, in which broken symmetries in configurations are restored using projection techniques. The low-lying energy spectrum is reasonably reproduced when the shape fluctuations in both the quadrupole and octupole shapes are considered. Electric octupole transition strength in ²²⁴Rn is found to be B(E3;31−→01+)=43 W.u., comparable to that in ²²⁴Ra, whose data are 42(3) W.u.. Our results indicate that ²²⁴Rn shares similar low-energy structure with ²²⁴Ra despite the excitation energy of first 3^- state of the former nucleus is higher than that of the latter. This study suggests ²²⁵Rn is a candidate for the search for permanent electric dipole moment.

153

In conventional isochronous mass spectrometry (IMS) performed on a storage ring, the precision of mass measurements for short-lived nuclei depends on the accurate determination of the revolution times (T) of stored ions. However, the resolution of T inevitably deteriorates due to the magnetic rigidity spread of the ions, limiting the mass-resolving power. In this study, we used the betatron tunes Q (the number of betatron oscillations per revolution) of the ions and established a correlation between T and Q. From this correlation, T was transformed to correspond to a fixed Q with higher resolution. Using these transformed T values, the masses of ⁶³Ge, ⁶⁵As, ⁶⁷Se, and ⁷¹Kr agreed well with the mass values measured using the newly developed IMS (Bρ-IMS). We also studied the systematics of Coulomb displacement energies (CDEs) and found that anomalous staggering in CDEs was eliminated using new mass values. This method of T transformation is highly effective for conventional IMS equipped with a single time-of-flight detector.

145

To ensure agreement between theoretical calculations and experimental data, parameters to selected nuclear physics models are perturbed and fine-tuned in nuclear data evaluations. This approach assumes that the chosen set of models accurately represents the 'true’ distribution of considered observables. Furthermore, the models are chosen globally, indicating their applicability across the entire energy range of interest. However, this approach overlooks uncertainties inherent in the models themselves. In this work, we propose that instead of selecting globally a winning model set and proceeding with it as if it was the 'true’ model set, we instead, take a weighted average over multiple models within a Bayesian Model Averaging (BMA) framework, each weighted by its posterior probability. The method involves executing a set of TALYS calculations by randomly varying multiple nuclear physics models and their parameters to yield a vector of calculated observables. Next, computed likelihood function values at each incident energy point were then combined with the prior distributions to obtain updated posterior distributions for selected cross sections and the elastic angular distributions. As the cross sections and elastic angular distributions were updated locally on a per-energy-point basis, the approach typically results in discontinuities or "kinks" in the cross section curves, and these were addressed using spline interpolation. The proposed Bayesian Model Averaging (BMA) method was applied to the evaluation of proton induced reactions on ⁵⁸Ni between 1 and 100 MeV. The results demonstrated a favorable comparison with experimental data as well as with the TENDL-2023 evaluation.

144

Short-lived medical isotopes and their generators are typically produced in nuclear reactors and cyclotrons that require extensive facilities. However, considering the environmental concerns and economic costs of these traditional approaches, modern laser technology, which provides extremely strong electric fields within tabletop-sized areas, can serve as a potential supplementary method. Focusing specifically on the (γ, p) generation of the vital medical isotopes ⁴⁷Sc and ⁶⁷Cu, we used both experimental results and PIC-GEANT4 simulations to demonstrate that laser-induced photonuclear reaction is a promising method for isotope production. We developed a model capable of calculating isotope yields under various laser conditions and acceleration mechanisms. The findings revealed that a 200 TW laser can sufficiently produce diagnostic amounts of ⁴⁷Sc and ⁶⁷Cu, while simultaneously providing high specific activity, which is significant in medical applications for improving treatment efficacy, enhancing image resolution, and reducing side effects.

198

Total absorption gamma ray spectroscopy (TAGS) is a powerful tool for measuring complex γ transitions, which has been effectively applied to the study of reactor decay heat. This paper presents the design of a new TAGS detector, the large-scale modular BGO detection array (LAMBDA), tailored for measuring β decay intensity distributions of fission products. The modular design allows the LAMBDA detector to be assembled in various configurations. The final version of LAMBDA consists of 102 identical 60 mm×60 mm×120 mm BGO crystals, and exhibits a high full-energy peak efficiency exceeding 80% at 0.5∼8 MeV based on a Monte Carlo simulation. Currently, approximately half of the LAMBDA modules have been manufactured. Tests using γ-ray sources and nuclear reactions demonstrated favorable energy resolution, energy linearity, and efficiency uniformity across the modules. Forty-eight modules have been integrated into the prototype LAMBDA-I. The capability of LAMBDA-I in β-delayed γ decay experiments was evaluated by commissioning measurements using the ¹⁵²Eu source.

173

The ¹²C+¹²C fusion is one of the most important reactions in modern nuclear astrophysics. The trend and magnitude of the reaction rate within the Gamow window strongly influence various astrophysical processes. However, direct measurement of this reaction is extremely difficult, which makes it necessary to develop indirect methods. In this study, the ²³Na + p reaction system was used to study the compound nucleus ²⁴Mg. We employed a thick-target inverse kinematics method combined with the γ-charged-particle coincidence technique to measure the proton and α exit channels of ²⁴Mg. Technical details of the ²³Na + p thick-target inverse kinematics experiment and analysis are presented herein.

186