分类: 物理学 >> 核物理学 提交时间: 2024-03-18
摘要: The exploration of exotic shapes and properties of atomic nuclei, e.g., α cluster and toroidal shape, is afascinating field in nuclear physics. To study the decay of these nuclei, a novel detector aimed at detectingmultiple alpha-particle events was designed and constructed. The detector comprises two layers of double-sidedsilicon strip detectors (DSSD) and a cesium iodide scintillator array coupled with silicon photomultipliers arrayas light sensors, which has the advantages of their small size, fast response, and large dynamic range. DSSDscouple with cesium iodide crystal arrays are used to distinguish multiple alpha hits. The detector array has acompact and integrated design that can be adapted to different experimental conditions. The detector array wassimulated using Geant4, and the excitation energy spectra of some alpha-clustering nuclei were reconstructedto demonstrate the performance. The simulation results show that the detector array has excellent angularand energy resolutions, enabling effective reconstruction of the nuclear excited state by multiple alpha particleevents. This detector offers a new and powerful tool for nuclear physics experiments and has the potential todiscover interesting physical phenomena related to exotic nuclear structures and their decay mechanisms
分类: 物理学 >> 核物理学 提交时间: 2024-03-18
摘要: In recent years, the gap between the supply and demand of medical radioisotopes has increased, necessitating new methods for producing medical radioisotopes. Photonuclear reactions based on gamma sources have unique advantages in terms of producing high specific activity and innovative medical radioisotopes. However, the lack of experimental data on reaction cross sections for photonuclear reactions of medical radioisotopes of interest has severely limited the development and production of photonuclear transmutation medical radioisotopes. In this study, the entire process of the generation, decay, and measurement of medical radioisotopes was simulated using online gamma activation and offline gamma measurements combined with a shielding gammaray spectrometer. Based on a quasi-monochromatic gamma beam from the Shanghai Laser Electron Gamma Source (SLEGS), the feasibility of the measurement of production cross section for surveyed medical isotopes was simulated, and specific solutions for measuring medical radioisotopes with low production cross sections were provided. The feasibility of this method for high precision measurements of the reaction cross section of medical radioisotopes was demonstrated.
分类: 物理学 >> 核物理学 提交时间: 2024-03-18
摘要: 通过在Nilsson势中引入八极关联相互作用,基于推转壳模型(CSM)下的粒子数守恒方法(PNC)处理包含单极和四极对力的哈密顿量,研究了反射不对称(RA)原子核的基态转动带。基于此,PNC-CSM的计算结果重现了轻锕系区偶偶核236,238U和238,240Pu的交替宇称带,以及奇-𝐴核237U和239Pu的宇称带双重带的转动惯量实验值。与相邻偶偶核236,238U和238,240Pu相比,奇-𝐴核237U和239Pu的𝑠=−𝑖内禀转动带的转动惯量增加了50%∼60%。这些增加的转动惯量主要是由费米面附近中子轨道的泡利堵塞效应减弱了中子体系的对关联导致。U和Pu同位素中,转动惯量随着转动频率缓慢增加则可以解释为转动使得体系的对关联减弱。在低频率区,反射不对称原子核的转动惯量明显高于相对应的反射对称(RS)原子核的转动惯量。并且,与反射对称原子核相比,较大的八极形变将导致反射不对称原子核体系的对关联减弱更加明显。
分类: 物理学 >> 核物理学 提交时间: 2024-03-13
摘要: Prompt radiation emitted during accelerator operation poses a significant health risk, necessitating a thorough search and securing of hazardous areas prior to initiation. Currently, manual sweep methods are employed. However, the limitations of manual sweeps have become increasingly evident with the implementation of large-scale accelerators. By leveraging advancements in machine vision technology, the automatic identification of stranded personnel in controlled areas through camera imagery presents a viable solution for efficient search and security. Given the criticality of personal safety for stranded individuals, search and security processes must be sufficiently reliable. To ensure comprehensive coverage, 180° camera groups were strategically positioned on both sides of the accelerator tunnel to eliminate blind spots within the monitoring range. The YOLOV8 network model was modified to enable the detection of small targets, such as hands and feet, as well as larger targets formed by individuals near the cameras. Furthermore, the system incorporates a pedestrian recognition model that detects human body parts, and an information fusion strategy is used to integrate the detected head, hands, and feet with the identified pedestrians as a cohesive unit. This strategy enhanced the capability of the model to identify pedestrians obstructed by equipment, resulting in a notable improvement in the recall rate. Specifically, recall rates of 0.915 and 0.82 were obtained for Datasets 1 and 2, respectively. Although there was a slight decrease in accuracy, it aligned with the intended purpose of the search-and-secure software design. Experimental tests conducted within an accelerator tunnel demonstrated the effectiveness of this approach in achieving reliable recognition outcomes.
分类: 物理学 >> 核物理学 提交时间: 2024-03-11
摘要: Fast neutron flux measurements with high count rates and high time resolution have important applications in equipment such as tokamaks. In this study, real-time neutron and gamma discrimination was implemented on a self-developed 500-Msps, 12-bit digitizer, and the neutron and gamma spectra were calculated directly on an FPGA . A fast neutron flux measurement system with BC-501A and EJ-309 liquid scintillator detectors was developed and a fast neutron measurement experiment was successfully performed on the HL-2M tokamak at the Southwestern Institute of Physics, China. The experimental results demonstrated that the system obtained the neutron and gamma spectra with a time accuracy of 1ms. At count rates of up to 1 Mcps, the figure of merit was greater than 1.05 for energies between 50 keV and 2.8 MeV.
分类: 物理学 >> 核物理学 提交时间: 2024-03-11
摘要: 聚变三乘积(Fusion triple product)是可自持核聚变反应的重要判据,它利用聚变堆中核燃料的原子核数密度$n$、等离子体约束时间$τ_ mathrm{E}$、燃料温度$T$这三个物理量来判断聚变反应堆是否能满足实现自持核聚变的能量平衡条件。本研究探讨了以$^{6}$Li-D作为核燃料的聚变反应系统,并考虑了相对论效应对轫致辐射的影响以及能量回收效率对能量增益因子$Q$的影响,计算了忽略回旋辐射条件下$^{6}$Li-D聚变反应系统的聚变三乘积($n_ mathrm{i}Tτ_{ mathrm{E}}$= SI{4.9e23}{ per cubic meter kilo electronvolt second})。结果表明,$^{6}$Li-D可以作为核聚变燃料实现正的能量增益,但其实现自持核聚变的点火条件相对于D-T核聚变的点火条件来说更为困难。
分类: 物理学 >> 核物理学 提交时间: 2024-03-10
摘要: Theutilization of a proton beam fromthe China Spallation Neutron Source (CSNS) for producingmedical radioisotopes is appealingowing toits high current intensity and high energy. The medical isotope production based on the proton beam at the CSNS is significantfor the development of futureradiopharmaceuticals, particularly for the α-emitting radiopharmaceuticals.The production yield and activity of typical medical isotopes wereestimated using theFLUKA simulation. The results indicate that the 300-MeV proton beam with a power of 100 kW at CSNS-II ishighly suitable for proof-of-principle studies of most medical radioisotopes. In particular, this proton beam offers tremendous advantages for the large-scale production of alpha radioisotopes, such as 225Ac, whose theoretical production yield can reach approximately57 Ci/week. Based on theseresults, we provideperspectives on the use ofCSNS proton beams to produce radioisotopes for medical applications.
分类: 物理学 >> 核物理学 提交时间: 2024-03-10
摘要: Currently, three types of superconducting magnets are used in particle accelerators: cos2uptheta, CCT, and serpentine. However, all three coil configurations have complex spatial geometries, which make magnet manufacturing and strain-sensitive superconductor applications difficult. Compared with the three existing quadrupole coils, the racetrack quadrupole coil has a simple shape and manufacturing process, but there have been few theoretical studies. In this paper, the two-dimensional and three-dimensional analytical expressions for the magnetic field in coil-dominated racetrack superconducting quadrupole magnets are presented. The analytical expressions of the field harmonics and gradient are fully resolved and depend only on the geometric parameters of the coil and current density. Then, a genetic algorithm is applied to obtain a solution for the coil geometry parameters with field harmonics on the order of 10-4. Finally, considering the practical engineering needs of the accelerator interaction region, electromagnetic design examples of racetrack quadrupole magnets with high gradients, large apertures, and small apertures are described, and the application prospects of racetrack quadrupole coils are analyzed.
分类: 物理学 >> 核物理学 提交时间: 2024-03-09
摘要: The study of nuclide production and its properties in the N=126 neutron-rich region is the frontier and hot topic in nuclear physics and astrophysics research. The upcoming High energy FRagment Separator (HFRS) at the High Intensity heavy-ion Accelerator Facility (HIAF), an in-flight separator at relativistic energies, is characterized by high beam intensity, large ion-optical acceptance, high magnetic rigidity, and high momentum resolution power. It provides an opportunity for the study of the production and properties of neutron-rich nuclei around N=126. In this paper, an experimental scheme is proposed to produce the neutron-rich nuclei around N=126 and simultaneously measure their mass and lifetime based on the HFRS separator, and the feasibility of this scheme is evaluated by the simulations. The results show that under the high resolution optical mode many new neutron-rich nuclei approaching the r-process abundance peak around A=195 can be produced for the first time, and many nuclei with unknown mass and lifetime can be produced with high statistics. Using the time-of-flight corrected by the measured dispersive position and the energy loss information, the cocktails produced from the 208Pb fragmentation can be unambiguously identified. Moreover, the masses of some neutron-rich nuclei in the vicinity of N=126 can be measured with high precision using the time-of-flight magnetic rigidity technique. This indicates that the HIAF-HFRS facility has potential for the production and property research of neutron-rich nuclei around N=126, which is of great significance for expanding chart of nuclides, developing nuclear theories, and understanding the origin of heavy elements in the universe.
分类: 物理学 >> 核物理学 提交时间: 2024-03-08
摘要: COMET is a leading experiment to search for coherent conversion of $ mu^- mathrm{N} to e^- mathrm{N}$ with a high-intensity pulsed muon beamline, produced by the innovative slow extraction techniques. Therefore, it is critical to measure the characteristics of the muon beam. We set up a Muon Beam Monitor (MBM), where scintillation fibers (SciFi) weaved in the cross shape are coupled to silicon photomultipliers (SiPM), to measure the spatial profile and timing structure of the extracted muon beam for COMET. The MBM detector has been tested successfully with a proton beamline in China Spallation Neutron Source (CSNS) and taken data with good performance in the commissioning run called COMET Phase-$ alpha$. Experience of the MBM development, such as the mechanical structure and electronics readout, and its beam measurement results will be shared.
分类: 物理学 >> 核物理学 提交时间: 2024-03-08
摘要: Neutron radiography is a crucial nondestructive testing technology widely used in the aerospace, military, andnuclear industries. However, because of the physical limitations of neutron sources and collimators, the resultingneutron radiographic images inevitably exhibit multiple distortions, including noise, geometric unsharpness,and white spots. Furthermore, these distortions are particularly significant in compact neutron radiography systemswith low neutron fluxes. Therefore, in this study, we devised a multi-distortion suppression network thatemploys a modified generative adversarial network to improve the quality of degraded neutron radiographic images.Real neutron radiographic image datasets with various types and levels of distortion were built for the firsttime as multi-distortion suppression datasets. Thereafter, the coordinate attention mechanism was incorporatedinto the backbone network to augment the capability of the proposed network to learn the abstract relationshipbetween ideally clear and degraded images. Extensive experiments were performed; the results show that theproposed method can effectively suppress multiple distortions in real neutron radiographic images and achievestate-of-the-art perceptual visual quality, thus demonstrating its application potential in neutron radiography.
分类: 物理学 >> 核物理学 提交时间: 2024-03-07
摘要: 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 surveillancedata 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 TTSresidual 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.
分类: 物理学 >> 核物理学 提交时间: 2024-03-04
摘要: 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 Ep = 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.
分类: 物理学 >> 核物理学 提交时间: 2024-03-04
摘要: The speed of sound in quark matter is an important physical quantity for studying the properties and the spacetime evolution of quark-gluon plasma (QGP). The behavior of the speed of sound with respect to temperature and density can reveal to some extent the equation of state and the phase structure of QGP. Building upon the previous studies on the speed of sound in symmetric quark matter, the formulae for calculating the speed of sound in asymmetric quark matter in the temperature-density space are further derived. The PNJL model is then used to calculate the dependence of the speed of sound on isospin asymmetry. Furthermore, the relationship between the magnitude of the speed of sound and the QCD phase structure is discussed, and the regions where the acoustic equation fails are indicated under different physical conditions.
分类: 物理学 >> 核物理学 提交时间: 2024-03-01
摘要: The exploration of spin symmetry (SS) in nuclear physics has been instrumental in identifyingatomic 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 stateswithin 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 asthe energy levels increase. We also analyzed the width of the resonant states, showing that lower orbital angularmomentum resonances possess shorter decay times and that SS is preserved within broad resonant doublets, asopposed to narrow resonant doublets. Comparing the radial density of the upper components for the bound-stateand 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 anincrease in β2 resulted in higher energy and width splitting in the resonant spin doublets, which is attributed toincreased component mixing. Furthermore, the sensitivity of spin doublets to various potential parameters suchas surface diffuseness (a), radius (R), and depth (Σ0) is discussed, emphasizing the role of these parametersin SS. This study provides valuable insights into the behavior of spin doublets in deformed nuclei and theirinterplay with the nuclear structure, thereby advancing our understanding of SS in the resonance state.
分类: 物理学 >> 核物理学 提交时间: 2024-02-29
摘要: The 28nm process has a high cost-performance ratio and has gradually become the standard for the fieldof radiation-hardened devices. However, owing to the minimum physical gate length of only 35nm, the physicalarea of a standard 6T SRAM unit is approximately 0.16 μm2, resulting in a significant enhancement ofmulti-cell charge-sharing effects. Multiple-cell upsets (MCUs) have become the primary physical mechanismbehind single-event upsets (SEUs) in advanced nanometer node devices. The range of ionization track effectsincreases with higher ion energies, and spacecraft in orbit primarily experience SEUs caused by high-energyions. However, ground accelerator experiments have mainly obtained low-energy ion irradiation data. Therefore,the impact of ion energy on the SEU cross-section, charge collection mechanisms, and MCU patterns andquantities in advanced nanometer devices remains unclear. In this study, based on the experimental platformof the Heavy Ion Research Facility in Lanzhou (HIRFL), low- and high-energy heavy-ion beams were usedto study the SEUs of 28nm SRAM devices. The influence of ion energy on the charge collection processesof small-sensitive-volume devices, MCU patterns, and upset cross-sections was obtained, and the applicablerange of the inverse-cosine law was clarified. The findings of this study are an important guide for the accurateevaluation of SEUs in advanced nanometer devices and for the development of radiation-hardening techniques.
分类: 物理学 >> 核物理学 分类: 物理学 >> 地球物理学、天文学和天体物理学 提交时间: 2024-02-29
摘要: It is hypothesized that, though atomic nuclei are made of nucleons, strongly interacting matter with baryon number from $A simeq 10^{3-9}$ to $ sim 10^{57}$ would be composed of strangeons if Nature favors always the flavor symmetry of quarks.According to that logic, strangeon matter with $A sim 10^{57}$ could manifest in the form of pulsar-like compact stars, and multi-messenger observations with advanced facilities (e.g., China’s FAST) could eventually provide a disproof/proof.It is worth emphasizing that this point of view, based on established “old physics”, may have particular consequences for understanding our material world, for both normal luminous matter and the dark sector.
分类: 核科学技术 >> 核科学技术其他学科 分类: 物理学 >> 核物理学 提交时间: 2024-02-28
摘要: Ferritic/martensitic (F/M) steels have been widely used as structural material for thermal and nuclear power plants. However, it is susceptible to intergranular damage in service conditions, which is expected to be critical issues. In order to improve the intergranular damage resistance of F/M steel, thermomechanical process (TMP) was employed to achieve a grain boundary engineering (GBE) microstructure in a kind of F/M steel P92 in this study. TMP, including cold rolling to 6%, 9%, and 12% thickness reduction, respectively, followed by austenization at 1323 K for 40 min plus tempering at 1053 K for 45 min, were applied on as-received (AR) P92 steel. Both prior austenite grain (PAG) size, prior austenite grain boundary character distribution (GBCD), and the connectivity of prior austenite grain boundaries (PAGBs) were investigated. Compared with AR specimen, the PAG size does not change significantly. The fraction of coincident site lattice boundaries (CSLBs, 3 ≤ Σ ≤ 29) and Σ3n boundaries along PAGBs decreases with increasing reduction ratio due to the recrystallization fraction increases with increasing reduction ratio. The PAGBs connectivity of the 6%-deformed specimen deteriorates compared with that of AR specimen slightly. Moreover, the potentiodynamic polarization studies revealed that the intergranular damage resistance of studied steel could be improved by enhancing the fraction of CSLBs along PAGBs, indicating that TMP, involving low deformation, could enhance the intergranular damage resistance.
分类: 物理学 >> 核物理学 提交时间: 2024-02-28
摘要: 介绍了上海光源线站工程之一的上海激光电子伽马源 (Shanghai Laser Electron Gamma Source, SLEGS)光束线站的建设与试运行情况,在SLEGS伽马源装置上可以开展核物理、核天体物理等基础研究、开展伽马辐照,伽马成像及伽马活化等应用研究。SLEGS光束线站在2021年12月通过工艺验收,2022年10月进入到试运行阶段,2023年9月对用户开放运行。SLEGS是国际上首台采用变换碰撞角度连续改变伽马束能量,具有最好的能量扫描精度、流强密度以及高效的能量调节能力。试运行阶段SLEGS光束线站重点解决了伽马束能谱和流强的在线监测问题,主要完成了平坦效率谱仪(FED)测量光中子截面的实验方法学研究,以及开展了伽马成像、伽马活化,正电子产生等应用平台的拓展和研究。随着逆康普顿散射技术的发展和应用需求的增加,未来短脉冲、高极化、高通量以及小型化的激光康普顿散射光源将会迎来更好的发展机遇,将在核物理、天体物理、粒子物理,极化物理,以及航空航天,医学检测,能源开发等伽马源应用研究领域发挥重要的作用。
分类: 物理学 >> 核物理学 提交时间: 2024-02-28
摘要: 上海激光电子伽马源(Shanghai Laser Electron Gamma Source,SLEGS)是通过激光与电子逆康普顿散射产生准单能、能量连续可调的兆电子伏伽马束,是目前国际上唯一一台可连续变换碰撞角度的激光康普顿散射(Laser Compton Scattering,LCS)伽马源装置。伽马活化是研究材料特性的有效手段之一,本文介绍了上海激光电子伽马源的伽马活化平台情况、包括在线活化过程,离线低本底测量,高纯锗(High Purity Germanium,HPGe)探测器的能量效率刻度等。目前的简易低本底屏蔽使得测量系统本底计数率降低到约 5.2cps/(60 keV-3 MeV 能区)。SLEGS 伽马源的活化平台为开展伽马活化测量研究提供了有利条件,未来在核物理、核天体物理、医学应用、材料科学和环境科学等领域的研究将会发挥重要的作用。