Abstract：The multi-physics instrument (MPI) is the first user cooperative instrument at the China Spallation Neutron Source (CSNS). It was designed to explore the structures of complex materials at multiple scales based on the neutron total scattering technique. This imposes the requirements for the detector, including a high detection efficiency to reduce the measurement time and a large solid angle coverage to cover a wide range of momentum transfers. To satisfy these demands, a large-area array of 3He-filled linear position-sensitive detectors (LPSDs) was constructed, each with a diameter of 1 inch and pressure of 20 atm. It uses an orbicular layout of the detector and an eight-pack module design for the arrangement of 3He LPSDs, covering a range of scattering angles from 3° to 170° with a total detector area of approximately 7 m2. The detector works in air, which is separated from the vacuum environment to facilitate installation and maintenance. The characteristics of the MPI detector were investigated through Monte Carlo (MC) simulations using Geant4 and experimental measurements. The results suggest that the detectors are highly efficient in the wavelength range of the MPI, and an efficiency over 25% is achievable for above 0.1 Å neutrons. A minimal position resolution of 6.4 mm full width at half maximum (FWHM) along the tube length was achieved at a working voltage of 2200 V, and a deviation below 2 mm between the real and measured positions was attained in the beam experiment. The detector module exhibited good consistency and an excellent counting rate capacity of up to 80 kHz, which satisfied the requirements of experiments with a high event rate. Observations of its operation over the past year have shown that the detector works steadily in sample experiments, which allows the MPI to serve the user program successfully.
Abstract：To reduce the experimental uncertainty in the 235U resonance energy region and improve the detection efficiency for neutron total cross-section measurements compared with those obtained with the neutron total cross-section spectrometer (NTOX), a dedicated lithium-containing scintillation detector has been developed on the Back-n beam line at the China Spallation Neutron Source (CSNS). The Fast Scintillator-based Neutron Total Cross Section (FAST) spectrometer has been designed based on a Cs2LiLaBr6 (CLLB) scintillator considering the γ-ray flash and neutron environment on the Back-n beam line. The response of the CLLB scintillator to neutrons and γ-rays was evaluated with different 6Li/7Li abundance ratios using Geant4. The neutron-γ discrimination performance of the CLLB has been simulated considering different scintillation parameters, physical designs, and light readout modes. A cubic 6Li-enriched (gt;90%) CLLB scintillator, which has a thickness of 4-9 mm and side length of no less than 50 mm to cover the Φ50 mm neutron beam at the spectrometer position, has been proposed coupling to a side-readout SiPM array to construct the FAST spectrometer. The developed simulation techniques for neutron-γ discrimination performance could provide technical support for other neutron-induced reaction measurements on the Back-n beam line.
Keywords：Neutron total cross section;CLLB scintillator;Geant4;Pulse shape discrimination(PSD)
Abstract：Nuclear security usually requires the simultaneous detection of neutrons and gamma rays. With the development of crystalline materials in recent years, Cs2LiLaBr6 (CLLB) dual-readout detectors have attracted extensive attention from researchers, where real-time neutron/gamma pulse discrimination is the critical factor among detector performance parameters. This study investigated the discrimination performance of the charge comparison, amplitude comparison, time comparison, and pulse gradient methods and the effects of a Sallen–Key filter on their performance. Experimental results show that the figure of merit (FOM) of all four methods is improved by proper filtering. Among them, the charge comparison method exhibits excellent noise resistance; moreover, it is the most suitable method of real-time discrimination for CLLB detectors. However, its discrimination performance depends on the parameters ts, tm, and te. When ts corresponds to the moment at which the pulse is at 10% of its peak value, te requires a delay of only 640 to 740 ns compared to ts, at which time the potentially optimal FOM of the charge comparison method at 3.1–3.3 MeV is greater than 1.46. The FOM obtained using the tm value calculated by a proposed maximized discrimination difference model(MDDM) and the potentially optimal FOM differ by less than 3.9%, indicating that the model can provide good guidance for parameter selection in the charge comparison method.
Abstract：In this study, we present the large photomultiplier tube (PMT) afterpulse measurement results obtained from the Jiangmen underground neutrino observatory (JUNO) experiment. A total of 11 dynode-PMTs (R12860) from the Hamamatsu company (Hamamatsu Photonics K.K. (HPK)) and 150 micro-channel plate PMTs (MCP-PMTs, GDB-6201) from the NNVT company (North Night Vision Technology Co., Ltd. (NNVT)) were tested. Subsequently, an afterpulse model was built according to the afterpulse time distribution and the probability of occurrence for these two types of PMTs. The average ratio of the total afterpulse charge with a delay between 0.5 μ s and 20 μ s to the primary pulse charge is ∼ 5.7% (13.2%) for the tested MCPPMTs (dynode-PMTs). The JUNO experiment will deploy 20,012 20-inch PMTs; this study will benefit detector simulation, event reconstruction, and data analysis regarding the JUNO experiment.
Abstract：The rapid development of advanced techniques for selective and efficient U(VI) extraction from aqueous solutions is essential for addressing U(VI) environmental pollution and energy issues. Here, we share recent progress in U(VI) extraction from aqueous solutions, especially the most frequently applied techniques such as adsorption, catalysis (photocatalysis, piezocatalysis, and electrocatalysis), chemical deposition, and reduction by zero-valent metal particles. We attempt to elucidate the strategies and various mechanisms that contribute to the enhancement of selective U(VI) extraction. At the end of our review, we highlight the outlook, challenges, and prospects for the development of this field.
Abstract：The inter-cycle correlation of fission source distributions (FSDs) in the Monte Carlo Power Iteration process results in variance underestimation of tallied physical quantities, especially in large local tallies. This study provides a mesh-free Semi-quantitative Variance Underestimation Elimination (SeVUE) method to obtain a credible confidence interval for the tallied results. This method comprises two procedures: Estimation and Elimination. The FSD inter-cycle correlation length is estimated in the Estimation procedure using the Sliced Wasserstein distance algorithm. The batch method was then used in the Elimination procedure. The FSD inter-cycle correlation length was proved to be the optimum batch length to eliminate the variance underestimation problem. We exemplified this method using the OECD sphere array model and 3D PWR BEAVRS model. The results showed that the average variance underestimation ratios of local tallies declined from 37% and 87% to within ±5% in these models.
Keywords：Monte Carlo algorithm;Power Iteration process;Inter-cycle correlation;Variance Underestimation;Sliced Wasserstein distance
Abstract：In a thorium-based molten salt reactor (TMSR), it is difficult to achieve the pure 232Th–233U fuel cycle without sufficient 233U fuel supply. Therefore, the original molten salt reactor was designed to use enriched uranium or plutonium as the starting fuel. By exploiting plutonium as the starting fuel and thorium as the fertile fuel, the high-purity 233U produced can be separated from the spent fuel by fluorination volatilization. Therefore, the molten salt reactor started with plutonium can be designed as a 233U breeder with the burning plutonium extracted from a pressurized water reactor (PWR). Combining these advantages, the study of the physical properties of plutonium-activated salt reactors is attractive. This study mainly focused on the burnup performance and temperature reactivity coefficient of a small modular molten-salt reactor started with plutonium (SM-MSR-Pu). The neutron spectra, 233U production, plutonium incineration, minor actinide (MA) residues, and temperature reactivity coefficients for different fuel salt volume fractions (VF) and hexagon pitch (P) sizes were calculated to analyze the burnup behavior in the SM-SMR-Pu. Based on the comparative analysis results of the burn-up calculation, a lower VF and larger P size are more beneficial for improving the burnup performance. However, from a passive safety perspective, a higher fuel volume fraction and smaller hexagon pitch size are necessary to achieve a deep negative feedback coefficient. Therefore, an excellent burnup performance and a deep negative temperature feedback coefficient are incompatible, and the optimal design range is relatively narrow in the optimized design of an SM-MSR-Pu. In a comprehensive consideration, P = 20 cm and VF = 20% are considered to be relatively balanced design parameters. Based on the fuel off-line batching scheme, a 250 MWth SM-MSR-Pu can produce approximately 29.83 kg of 233U, incinerate 98.29 kg of plutonium, and accumulate 14.70 kg of MAs per year, and the temperature reactivity coefficient can always be lower than -4.0 pcm/K.
Keywords：Molten salt fuel;Incinerate plutonium;233U production;Temperature reactivity coefficient
Abstract：A lead-shielded HPGe detector and offline γ–ray spectra of the residual product were used to measure the cross-section (CS) and ratios of isomeric CS (σm/σg) in 134Xe(n,2n)133m,gXe reactions at different energies (13.5 MeV, 13.8 MeV, 14.1 MeV, 14.4 MeV, 14.8 MeV) relative to the 93Nb(n,2n)92mNb reaction CS. The target was high-purity natural Xe gas under high pressure. The T(d,n)4He reaction produces neutrons. TALYS code (version 1.95) for nuclear reactions was used for calculations, with default parameters and nuclear level density models. The uncertainties in the measured CS data were thoroughly analyzed using the covariance analysis method. The results were compared with theoretical values, evaluation data, and previous experimental findings. CS data of the 134Xe(n,2n)133mXe and 134Xe(n,2n)133gXe reactions and the corresponding isomeric CS ratios at 13.5 MeV, 13.8 MeV, and 14.1 MeV neutron energies are reported for the first time. This research advances our knowledge of pre-equilibrium emission in the (n,2n) reaction channel by resolving inconsistencies in the Xe data.
Abstract：Approaches for predicting low-lying resonances, uniformly treating bound, and resonant levels, have been a long-standing goal in nuclear theory. Accordingly, we explored the viability of the complex momentum representation (CMR) approach coupled with new potentials. We focus on predicting the energy of the low-lying 2p3/2 resonance in 17O, which is critical for s-process nucleosynthesis and missing in previous theoretical research. Using a Woods-Saxon potential based on the Koning-Delaroche optical model and constrained by the experimental one-neutron separation energy, we successfully predicted the resonant energy of this level for the first time. Our predictions of the bound levels and 1d3/2 resonance agree well with the measurement results. Additionally, we utilize this approach to study the near-threshold resonances that play a role when forming a two-neutron halo in 29, 31F. We found that the CMR-based predictions of the bound level energies and unbound 1f7/2 level agree well with the results obtained using the scattering phase shift method. Subsequently, we successfully found a solution for the 2p3/2 resonance with energy just above the threshold, which is decisive for halo formation.
Keywords：Neutron capture;Low-lying resonance;CMR;Resonance energy
Abstract：In the framework of the dinuclear system model, the synthesis mechanism of the superheavy nuclides with atomic numbers Z=112, 114, 115 in the reactions of projectiles 40,48Ca bombarding on targets 238U, 242Pu, and 243Am within a wide interval of incident energy has been investigated systematically. Based on the available experimental excitation functions, the dependence of calculated synthesis cross-sections on collision orientations has been studied thoroughly. The total kinetic energy (TKE) of these collisions with fixed collision orientation shows orientation dependence, which can be used to predict the tendency of kinetic energy diffusion. The TKE is dependent on incident energies, as discussed in this paper. We applied the method based on the Coulomb barrier distribution function in our calculations. This allowed us to approximately consider all the collision orientations from tip-tip to side-side. The calculations of excitation functions of 48Ca + 238U, 48Ca + 242Pu, and 48Ca + 243Am are in good agreement with the available experimental data. The isospin effect of projectiles on production cross-sections of moscovium isotopes and the influence of the entrance channel effect on the synthesis cross-sections of superheavy nuclei are also discussed in this paper. The synthesis cross-section of new moscovium isotopes 278-286Mc was predicted to be as large as hundreds of pb in the fusion-evaporation reactions of 35,37Cl + 248Cf, 38,40Ar + 247Bk, 39,41K + 247Cm, 40,42,44,46Ca + 243Am, 45Sc + 244Pu, and 46,48,50Ti + 237Np, 51V + 238U at some typical excitation energies.
Keywords：Dinuclear system model;Superheavy nuclei;Complete fusion reactions;Production cross-section
Abstract：β-decay half-life and β-delayed neutron emission (βn) are of great importance in the development of basic science and industrial applications, such as nuclear physics and nuclear energy, where β--decay plays an important role. Many theoretical models have been proposed to describe β-decay half-lives, whereas the systematic study of βn is still rare. This study aimed to investigate β--decay half-lives and βn probabilities through analytical formulas and by comparing them with experimental data. Analytical formulas for β--decay properties have been proposed by considering prominent factors, that is, decay energy, odevity, and the shell effect. The bootstrap method was used to simultaneously evaluate the total uncertainty on calculations, which was composed of statistic and systematic uncertainties. β--decay half-lives, βn probabilities, and the corresponding uncertainties were evaluated for the neutron-rich region. The experimental half-lives were well reproduced. Additional predictions are also presented with theoretical uncertainties, which helps to better understand the disparity between the experimental and theoretical results.
Abstract：The cavity-based X-ray free-electron laser (XFEL) has promise in producing fully coherent pulses with a bandwidth of a few meV and very stable intensity, whereas the currently existing self-amplified spontaneous emission (SASE) XFEL is capable of generating ultra-short pulses with chaotic spectra. In general, a cavity-based XFEL can provide a spectral brightness three orders of magnitude higher than that of the SASE mode, thereby opening a new door for cutting-edge scientific research. With the development of superconducting MHz repetition-rate XFEL facilities such as FLASH, European-XFEL, LCLS-II, and SHINE, practical cavity-based XFEL operations are becoming increasingly achievable. In this study, Megahertz cavIty eNhanced x-ray Generation (MING) is proposed based on China’s first hard XFEL facility — SHINE, which we refer to as MING@SHINE.
Keywords：X-ray free-electron laser;Free electron laser oscillator;Fully coherent X-ray
Abstract：Proton FLASH therapy with an ultra-high dose rate is in urgent need of more accurate treatment plan system (TPS) to promote the development of proton computed tomography (CT) without intrinsic error compared with the transformation from X-ray CT. This paper presents an imaging mode of proton CT based on static superconducting gantry different from the conventional rotational gantry. The beam energy for proton CT is fixed at 350 MeV, which is boosted by a compact proton linac from 230 MeV, and then delivered by the gantry to scan the patient’s body for proton imaging. This study demonstrates that the static superconducting gantry-based proton CT is effective in clinical applications. In particular, the imaging mode, which combines the relative stopping power (RSP) map from X-ray CT as prior knowledge, can produce much a higher accuracy RSP map for TPSs and positioning and achieve ultra-fast image for real-time image-guided radiotherapy (IGRT). This paper presents the conceptual design of a boosting linac, static superconducting gantry and proton CT imaging equipment. The feasibility of energy enhancement is verified by simulation, and results from Geant4 simulations and reconstruction algorithms are presented, including the simulation verification of the advantage of the imaging mode.
Abstract：Owing to the constraints on the fabrication of γ-ray coding plates with many pixels, few studies have been carried out on γ-ray computational ghost imaging. Thus, the development of coding plates with fewer pixels is essential to achieve γ-ray computational ghost imaging. Based on the regional similarity between Hadamard subcoding plates, this study presents an optimization method to reduce the number of pixels of Hadamard coding plates. First, a moving distance matrix was obtained to describe the regional similarity quantitatively. Second, based on the matrix, we used two ant colony optimization arrangement algorithms to maximize the reuse of pixels in the regional similarity area and obtain new compressed coding plates. With full sampling, these two algorithms improved the pixel utilization of the coding plate, and the compression ratio values were 54.2% and 58.9%, respectively. In addition, three undersampled sequences (the Harr, Russian dolls, and cake-cutting sequences) with different sampling rates were tested and discussed. With different sampling rates, our method reduced the number of pixels of all three sequences, especially for the Russian dolls and cake-cutting sequences. Therefore, our method can reduce the number of pixels, manufacturing cost, and difficulty of the coding plate, which is beneficial for the implementation and application of γ-ray computational ghost imaging.