Vol.35,

Online γ-spectrometry systems for inland waters, most of which extract samples in situ and in real time, are able to produce reliable activity concentration measurements for waterborne radionuclides only when they are distributed relatively uniformly and enter into a steady-state (SS) diffusion regime in the measurement chamber. To protect residents’ health and ensure the safety of the living environment, better timeliness is required for this measurement method. To address this issue, this study established a mathematical model of the online water γ-spectrometry system so that rapid warning and activity estimates can be obtained for water under non-steady-state (NSS) conditions. In addition, the detection efficiency of the detector for radionuclides during the NSS diffusion process was determined by applying the computational fluid dynamics (CFD) technique in conjunction with Monte Carlo simulations. On this basis, a method was developed that allowed the online water -spectrometry system to provide rapid warning and activity concentration estimates for radionuclides in water. Subsequent analysis of the NSS-mode measurements of ⁴⁰K radioactive solutions with different activity concentrations determined the optimum warning threshold and measurement time for producing accurate activity concentration estimates for radionuclides. The experimental results show that the proposed NSS measurement method is able to give warning and yield accurate activity concentration estimates for radionuclides 55.42 and 69.42 min after the entry of a 10 Bq/L ⁴⁰K radioactive solution into the measurement chamber, respectively. These times are much shorter than the 90 min required by the conventional measurement method. Furthermore, the NSS measurement method allows the measurement system to give rapid (within approximately 15 min) warning when the activity concentrations of some radionuclides reach their respective limits stipulated in the Guidelines for Drinking-water Quality of the WHO, suggesting that this method considerably enhances the warning capacity of in situ online water γ-spectrometry systems.

726

The most critical part of a neutron computed tomography (NCT) system is the image processing algorithm, which directly affects the quality and speed of the reconstructed images. Various types of noise in the system can degrade the quality of the reconstructed images. Therefore, to improve the quality of the reconstructed images of NCT systems, efficient image processing algorithms must be used. The anisotropic diffusion filtering (ADF) algorithm can not only effectively suppress the noise in the projection data, but also preserve the image edge structure information by reducing the diffusion at the image edges. Therefore, we propose the application of the ADF algorithm for NCT image reconstruction. To compare the performance of different algorithms in NCT systems, we reconstructed images using the ordered subset simultaneous algebraic reconstruction technique (OS-SART) algorithm with different regular terms as image processing algorithms. In the iterative reconstruction, we selected two image processing algorithms, the Total Variation and split Bregman solved total variation algorithms, for comparison with the performance of the ADF algorithm. Additionally, the filtered back-projection algorithm was used for comparison with an iterative algorithm. By reconstructing the projection data of the numerical and clock models, we compared and analyzed the effects of each algorithm applied in the NCT system. Based on the reconstruction results, OS-SART-ADF outperformed the other algorithms in terms of denoising, preserving the edge structure, and suppressing artifacts. For example, when the 3D Shepp-Logan was reconstructed at 25 views, the root mean square error of OS-SART-ADF was the smallest among the four iterative algorithms, at only 0.0292. The universal quality index, mean structural similarity, and correlation coefficient of the reconstructed image were the largest among all algorithms, with values of 0.9877, 0.9878, and 0.9887, respectively.

787

We report on using synthetic silicon for a high-precision X-ray polarimeter comprising a polarizer and an analyzer, each based on a monolithic channel-cut crystal used at multiple Brewster reflections with a Bragg angle very close to 45°. Experiments were performed at the BL09B bending magnet beamline of the Shanghai Synchrotron Radiation Facility using a Si(800) crystal at an X-ray energy of 12.914 keV. A polarization purity of 8.4×10^-9was measured. This result is encouraging, as the measured polarization purity is the best-reported value for the bending magnet source. Notably, this is the firstly systematic study on the hard X-ray polarimeter in China, which is crucial for exploring new physics, such as verifying vacuum birefringence.

607

In high-altitude nuclear detonations, the proportion of pulsed X-ray energy can exceed 70%, making it a specific monitoring signal for such events. These pulsed X-rays can be captured using a satellite-borne X-ray detector following atmospheric transmission. To quantitatively analyze the effects of different satellite detection altitudes, burst heights, and transmission angles on the physical processes of X-ray transport and energy fluence, we developed an atmospheric transmission algorithm for pulsed X-rays from high-altitude nuclear detonations based on scattering correction. The proposed method is an improvement over the traditional analytical method that only computes direct-transmission X-rays. The traditional analytical method exhibits a maximum relative error of 67.79% compared with the Monte Carlo method. Our improved method reduces this error to within 10% under the same conditions, even reaching 1% in certain scenarios. Moreover, its computation time is 48000 times faster than that of the Monte Carlo method. These results have important theoretical significance and engineering application value for designing satellite-borne nuclear detonation pulsed X-ray detectors, inverting nuclear detonation source terms, and assessing ionospheric effects.

542

Space objects such as spacecraft or missiles may be exposed to intense X-rays in outer space, leading to severe damage. The reinforcement of these objects to reduce the damage caused by X-ray irradiation is a significant concern. The blow-off impulse (BOI) is a crucial physical quantity for investigating material damage induced by X-ray irradiation. However, the accurate calculation of BOI is challenging, particularly for large deformations of materials with complex configurations. In this study, we develop a novel two-dimensional particle-in-cell (PIC) code, Xablation2D, to calculate BOIs under far-field X-ray irradiation. This significantly reduces the dependence of the numerical simulation on the grid shape. The reliability of this code is verified by simulation results from open-source codes, and the calculated BOIs are consistent with the experimental and analytical results.

606

In this study, the interactions between a Ga-based liquid metal, GaInSn, and several metal materials, including pure metals (Ni and Ti) and alloys (316H stainless steel (SS) and GH3535), at 650 °C were investigated. The aim was to evaluate the corrosion performance and select a suitable candidate material for use as a molten salt manometer diaphragm in thermal energy storage systems. The results indicated that the alloys (316H SS and GH3535) exhibited less corrosion than pure metals (Ni and Ti) in liquid GaInSn. Ga-rich binary intermetallic compounds were found to form on the surfaces of all the tested metal materials exposed to liquid GaInSn, as a result of the decomposition of liquid GaInSn and its reaction with the constituent elements of the metal materials. The corrosion mechanism for all the tested materials exposed to liquid GaInSn was also investigated and proposed, which may aid in selecting the optimal candidate material when liquid GaInSn is used as the pressure-sensing medium.

514

The helium bubbles induced by 14 MeV neutron irradiation can cause intergranular fractures in reduced activation ferritic martensitic (RAFM) steel, which is a candidate structural material for fusion reactors. In order to elucidate the susceptibility of different grain boundaries (GBs) to helium-induced embrittlement, the tensile fracture processes of 10 types of GBs with and without helium bubbles in body-centered cubic (bcc) iron at the relevant service temperature of 600 K were investigated via molecular dynamics methods. The results indicate that in the absence of helium bubbles, the GBs studied here can be classified into two distinct categories: brittle GBs and ductile GBs. The atomic scale analysis shows that the plastic deformation of ductile GB at high temperatures originates from complex plastic deformation mechanisms, including the Bain/Burgers path phase transition and deformation twinning, in which the Bain path phase transition is the most dominant plastic deformation mechanism. However, the presence of helium bubbles severely inhibits the plastic deformation channels of the GBs, resulting in a significant decrease in elongation at fractures. For bubble-decorated GBs, the ultimate tensile strength increases with the increase of the misorientation angle. Interestingly, the coherent twin boundary Ʃ3{112} was found to maintain relatively high fracture strength and maximum failure strain under the influence of helium bubbles.

438

The synergistic damage effect of irradiation and corrosion of reactor structural materials has been a prominent research focus. This paper provides a comprehensive review of the synergistic effects on the third- and fourth-generation fission nuclear energy structural materials used in pressurized water reactors and molten salt reactors. The competitive mechanisms of multiple influencing factors, such as the irradiation dose, corrosion type, and environmental temperature, are summarized in this paper. Conceptual approaches are proposed to alleviate the synergistic damage caused by irradiation and corrosion, thereby promoting in-depth research in the future and solving this key challenge for the structural materials used in reactors.

786

A new measurement method for the spatial distribution of neutron beam flux in boron neutron capture therapy (BNCT) is being developed based on the two-dimensional Micromegas detector. To address the issue of long processing times in traditional offline position reconstruction methods, this paper proposes a field programmable gate array (FPGA) based online position reconstruction method utilizing the micro time projection chamber principle. This method encapsulates key technical aspects: a self-adaptive serial link technique built upon the dynamical adjustment of the delay chain length, fast sorting, a coordinate-matching technique based on the mapping between signal timestamps and random access memory (RAM) addresses, and a precise start point-merging technique utilizing a circular combined RAM. The performance test of the self-adaptive serial link shows that the bit error rate of the link is better than 10^-12 at a confidence level of 99%, ensuring reliable data transmission. The experiment utilizing the readout electronics and Micromegas detector shows a spatial resolution of approximately 1.4 mm, surpassing the current method’s resolution level of 5 mm. The beam experiment confirms that the readout electronics system can obtain the flux spatial distribution of neutron beams online, thus validating the feasibility of the position reconstruction method. The online position reconstruction method avoids traditional methods, such as bubble sorting and traversal searching, simplifies the design of the logic firmware, and reduces the time complexity from O(n²) to O(n). This study contributes to the advancement in measuring neutron beam flux for BNCT.

409

Topmetal-M2 is a large-area pixel sensor chip fabricated using the GSMC 130 nm CMOS process in 2021. The pixel array of Topmetal-M2 consists of pixels of 400 rows × 512 columns with a pixel pitch of 45 μm × 45 μm. The array is divided into 16 subarrays, with pixels of 400 rows × 32 columns per subarray. Each pixel incorporates two charge sensors: a diode sensor and a Topmetal sensor. The in-pixel circuit primarily consists of a charge-sensitive amplifier for energy measurements, a discriminator with a peak-holding circuit, and a time-to-amplitude converter for time-of-arrival measurements. The pixel of Topmetal-M2 has a charge input range of ~0-3 ke^-, a voltage output range of ~0-180 mV, and a charge-voltage conversion gain of ~59.56 μV/e^-. The average equivalent noise charge of Topmetal-M2, which includes the readout electronic system noise, is ~43.45 e^-. In the scanning mode, the time resolution of Topmetal-M2 is 1 LSB=1.25 μs, and the precision is ~7.41 μs. At an operating voltage of 1.5 V, Topmetal-M2 has a power consumption of ~49mW/cm². In this article, we provide a comprehensive overview of the chip architecture, pixel working principles, and functional behavior of Topmetal-M2. Furthermore, we present the results of preliminary tests conducted on Topmetal-M2, namely, alpha-particle and soft X-ray tests.

488

The BETA application-specific integrated circuit (ASIC) is a fully programmable chip designed to amplify, shape, and digitize the signal of up to 64 Silicon photomultiplier (SiPM) channels, with a power consumption of approximately ~1 mW/channel. Owing to its dual-path gain, the BETA chip is capable of resolving single photoelectrons (phes) with a signal-to-noise ratio (SNR) >5 while simultaneously achieving a dynamic range of ~~4000 phes. Thus, BETA can provide a cost-effective solution for the readout of SiPMs in space missions and other applications with a maximum rate below 10 kHz. In this study, we describe the key characteristics of the BETA ASIC and present an evaluation of the performance of its 16-channel version, which is implemented using 130 nm technology. The ASIC also contains two discriminators that can provide trigger signals with a time jitter down to 400 ps FWHM for 10 phes. The linearity error of the charge gain measurement was less than 2% for a dynamic range as large as 15 bits.

645

Boron neutron capture therapy (BNCT) is recognized as a precise binary targeted radiotherapy technique that effectively eliminates tumors through the ¹⁰B(n,α)⁷Li nuclear reaction. Among various neutron sources, accelerator-based sources have emerged as particularly promising for BNCT applications. The ⁷Li(p,n)⁷Be reaction is highly regarded as a potential neutron source for BNCT, owing to its low threshold energy for the reaction, significant neutron yield, appropriate average neutron energy, and additional benefits. This study utilized Monte Carlo simulations to model the physical interactions within a lithium target subjected to proton bombardment, including neutron moderation by an MgF₂ moderator and subsequent BNCT dose analysis using a Snyder head phantom. The study focused on calculating the yields of epithermal neutrons for various incident proton energies, finding an optimal energy at 2.7 MeV. Furthermore, the Snyder head phantom was employed in dose simulations to validate the effectiveness of this specific incident energy when utilizing a ⁷Li (p,n)⁷Be neutron source for BNCT purposes.

451

Based on the unified Hauser–Feshbach and exciton model, which can describe the particle emission processes between discrete energy levels with energy, angular momentum, and parity conservations, a statistical theory of light nucleus reaction (STLN) is developed to calculate the double-differential cross-sections of the outgoing neutron and light charged particles for the proton-induced ⁶Li reaction. A significant difference is observed between the p + ⁶Li and p + ⁷Li reactions owing to the discrepancies in the energy-level structures of the targets. The reaction channels, including sequential and simultaneous emission processes, are analyzed in detail. Taking the double-differential cross-sections of the outgoing proton as an example, the influence of contaminations (such as ¹H, ⁷Li, ¹²C, and ¹⁶O) on the target is identified in terms of the kinetic energy of the first emitted particles. The optical potential parameters of the proton are obtained by fitting the elastic scattering differential cross-sections. The calculated total double-differential cross-sections of the outgoing proton and deuteron at E_p = 14 MeV agree well with the experimental data for different outgoing angles. Simultaneously, the mixed double differential cross-sections of ³He and α are in good agreement with the measurements. The agreement between the measured data and calculated results indicates that the two-body and three-body breakup reactions need to be considered, and the pre-equilibrium reaction mechanism dominates the reaction processes. Based on the STLN model, a PLUNF code for the p + ⁶Li reaction is developed to obtain an ENDF-6-formatted file of the double-differential cross-sections of the nucleon and light composite charged particles.

597

Using the Skyrme density functional theory (DFT), potential energy surfaces (PES) of ²⁴⁰Pu with constraints on the axial quadrupole and octupole deformations(q₂₀ and q₃₀) were calculated. The volume-like and surface-like pairing forces, as well as a combination of these two forces were used for the Hartree-Fock-Bogoliubov (HFB) approximation. Variations in the least-energy fission path, fission barrier, pairing energy, total kinetic energy, scission line, and mass distribution of the fission fragments based on the different forms of the pairing forces were analyzed and discussed. The fission dynamics were studied based on the time-dependent generator coordinate method (TDGCM) plus the Gaussian overlap approximation (GOA). The results demonstrated a sensitivity of the mass and charge distributions of the fission fragments on the form of the pairing force. Based on the investigation of the neutron-induced fission of ²³⁹Pu, among the volume, mixed, and surface pairing forces, the mixed pairing force presented a good reproduction of the experimental data.

490

Big Bang nucleosynthesis (BBN) theory predicts the primordial abundances of the light elements ²H (referred to as deuterium, or D for short), ³He, ⁴He, and ⁷Li produced in the early universe. Among these, deuterium, the first nuclide produced by BBN, is a key primordial material for subsequent reactions. To date, the uncertainty in predicted deuterium abundance (D/H) remains larger than the observational precision. In this study, the Monte Carlo simulation code PRIMAT was used to investigate the sensitivity of 11 important BBN reactions to deuterium abundance. We found that the reaction rate uncertainties of the four reactions d(d,n)³He, d(d,p)t, d(p,γ)³He, and p(n,γ)d had the largest influence on the calculated D/H uncertainty. Currently, the calculated D/H uncertainty cannot reach observational precision even with the recent LUNA precise d(p,γ)³He rate. From the nuclear physics aspect, there is still room to largely reduce the reaction-rate uncertainties; hence, further measurements of the important reactions involved in BBN are still necessary. A photodisintegration experiment will be conducted at the Shanghai Laser Electron Gamma Source (SLEGS) Facility to precisely study the deuterium production reaction of p(n,γ)d.

512

The distribution of the nuclear ground-state spin in a two-body random ensemble (TBRE) was studied using a general classification neural network (NN) model with two-body interaction matrix elements as input features and the corresponding ground-state spins as labels or output predictions. The quantum many-body system problem exceeds the capability of our optimized NNs in terms of accurately predicting the ground-state spin of each sample within the TBRE. However, our NN model effectively captured the statistical properties of the ground-state spin because it learned the empirical regularity of the ground-state spin distribution in TBRE, as discovered by physicists.

513

The yield ratios of neutron-proton (R(n/p)) and ³H-³He (R(³H/³He)) with reduced rapidity from 0 to 0.5 were simulated at 50 MeV/u even-even ^36-56Ca + ⁴⁰Ca, even-even ^48-78Ni + ⁵⁸Ni, and ^100-139Sn (every third isotopes) + ¹¹²Sn for full reduced impact parameters using the isospin-dependent quantum molecular dynamics (IQMD) model. The neutron and proton density distributions and root-mean-square radii of the reaction systems were obtained using the Skyrme-Hartree-Fock model, which was used for the phase space initialization of the projectile and target in IQMD. We defined the unified neutron skin thickness as ΔRnp=〈r2〉n1/2−〈r2〉p1/2, which was negative for neutron-deficient nuclei. The unified ΔRnp values for nuclei with the same relative neutron excess from different isotopic chains were nearly equal, except for extreme neutron-rich isotopes, which is a type of scaling behavior. The yield ratios of the three isotopic chain-induced reactions, which depended on the reduced impact parameter and unified neutron skin thickness, were studied. The results showed that both R(n/p) and R(³H/³He) decreased with a reduced impact parameter for extreme neutron-deficient isotopes; however, they increased with reduced impact parameters for extreme neutron-rich isotopes, and increased with the ΔRnp of the projectiles for all reduced impact parameters. In addition, a scaling phenomenon was observed between ΔRnp and the yield ratios in peripheral collisions from different isotopic chain projectiles (except for extreme neutron-rich isotopes). Thus, R(n/p) and R(³H/³He) from peripheral collisions were suggested as experimental probes for extracting the neutron or proton skin thicknesses of non-extreme neutron-rich nuclei from different isotopic chains.

437

The exploration of spin symmetry (SS) in nuclear physics has been instrumental in identifying atomic nucleus structures. In this study, we solve the Dirac equation from the relativistic mean field (RMF) in complex momentum representation. We investigated SS and its breaking in single-particle resonant states within deformed nuclei, with a focus on the illustrative nucleus ¹⁶⁸Er. This was the initial discovery of a resonant spin doublet in a deformed nucleus, with the expectation of the SS approaching the continuum threshold. With increasing single-particle energy, the splitting of the resonant spin doublets widened significantly. This escalating splitting implies diminishing adherence to the SS, indicating a departure from the expected behavior as the energy levels increase. We also analyzed the width of the resonant states, showing that lower orbital angular momentum resonances possess shorter decay times and that SS is preserved within broad resonant doublets, as opposed to narrow resonant doublets. Comparing the radial density of the upper components for the bound-state and resonant-state doublets, it becomes evident that while SS is well-preserved in the bound states, it deteriorates in the resonant states. The impact of nuclear deformation (β₂) on SS was examined, demonstrating that an increase in β₂ resulted in higher energy and width splitting in the resonant spin doublets, which is attributed to increased component mixing. Furthermore, the sensitivity of spin doublets to various potential parameters such as surface diffuseness (a), radius (R), and depth (∑₀) is discussed, emphasizing the role of these parameters in SS. This study provides valuable insights into the behavior of spin doublets in deformed nuclei and their interplay with the nuclear structure, thereby advancing our understanding of SS in the resonance state.

570