分类： 物理学 >> 核物理学 提交时间： 2024-05-24
摘要： The recently discovered, extremely proton-rich nuclide18Mg exhibits ground-state decay via two sequential two-proton (2p) emissions through the intermediate nucleus,16Ne. This study investigates the structure and the initial2pdecay mechanism of18Mgby examining the density and correlations of the valence protons using a three-body Gamow-coupled-channel method. The results show that the ground state of18Mgis significantly influenced by the continuum, resulting in a significants-wave component. However, based on the current frame- work, this does not lead to a significant deviation in mirror symmetry in either the structure or spectroscopy of the18Mg-18Cpair. Additionally, the time evolution analysis of the18Mgground state suggests a simultaneous2pemission during the first step of decay. The observed nucleon–nucleon correlations align with those of the light–mass2pemitters, indicating a consistent decay behavior within this nuclear region.
分类： 核科学技术 >> 核探测技术与核电子学 提交时间： 2024-05-21
摘要： 为了适配闪烁体与硅光电倍增管（Silicon photomultiplier, SiPM）耦合探测器的不同应用场景，设计了基于OPA855芯片的跨阻放大器（Transimpedance Amplifier, TIA）和电压反馈放大器（Voltage Feedback Amplifier, VFB）。跨阻放大器的带宽为101MHz低于电压反馈放大器的381MHz，但其基线噪声 σnoise≅ 448.32μV优于电压反馈放大器的 σnoise≅ 680.96μV。实验结果表明：两类前置放大器均可提供高带宽和低输入噪声，并用于SiPM不同的输出模式。室温下，采用SiPM耦合掺铈钆铝镓石榴石（Cerium-doped Gadolinium Aluminum Gallium Garnet, GAGG(Ce)）探头对 241Am源进行信号测量，分析了SiPM标准输出脉冲和快输出脉冲的影响因素和适用场景。
分类： 核科学技术 >> 核科学与技术 提交时间： 2024-05-23
摘要： 目前压水堆电厂控制以传统PID (Proportional Integral Derivative) 控制器为主，虽然已有采用先进控制算法提升控制系统性能的研究，但大多都只针对单个控制系统，未能充分考虑多个控制系统之间存在的互联耦合。为了从顶层协调多个控制系统提升整体控制性能，本文提出了基于粒子群优化算法的压水堆控制系统设定值决策优化方法，构建了优化所需的决策目标函数及决策优化需要满足的运行约束条件。建立的智能决策系统，考虑压水堆的运行实际进行设定值离线优化，根据运行工况进行在线智能决策。本文以压水堆核电厂运行中的典型过程为例进行了设计的智能决策系统仿真实验，并对仿真结果进行分析，仿真结果表明所提出的智能决策系统可以有效减小系统的ITSE和峰值，提升了压水堆电厂控制系统的整体控制性能和安全裕量。
分类： 核科学技术 >> 核探测技术与核电子学 提交时间： 2024-05-27
摘要： Shielding material is critical for downhole pulsed neutron tool design as it directly influences the accuracy of formation measurements. A well-designed shield configuration ensures that the response of the tool is maximally representative of formation without being impacted by tool and borehole environment. This manuscript investigates the effects of boron-containing materials on neutron and gamma detectors based on a newly designed logging-while-drilling tool, which is currently undergoing manufacturing process. As boron content increases, its ability to absorb thermal neutrons significantly enhances. Through simulation, it is proven that boron carbide (B4C) can be used as an effective boron shielding material for thermal neutrons and therefore employed in this work. To shield against thermal neutrons migrating from mud pipes, the optimal shielding thicknesses for near and far neutron detectors are determined to be 5mm and 4mm. For an example, at a porosity of 25 p.u., the near neutron sensitivity shows a 5.6% increase in response. Furthermore, in order to shield capture gamma generated by thermal neutrons once they enter tool from the mud pipe and formation, the internal and external shields for the gamma detector is evaluated. Results show internal shield needs 75% boron content while the external shield is of 14.2mm thickness and 25% boron content to minimize tool effect.
分类： 核科学技术 >> 辐射物理与技术 提交时间： 2024-05-26
摘要： The Very Large Area gamma-ray Space Telescope (VLAST) is a mission concept proposed to detect gamma#2;ray photons through both Compton scattering and electron-positron pair production mechanisms, thus enablingthe detection of photons with energies ranging from MeV to TeV. This project aims to conduct a comprehensivesurvey of the gamma-ray sky from a low-Earth orbit using an anti-coincidence detector, a tracker detectorthat also serves as a low-energy calorimeter, and a high-energy imaging calorimeter. We developed a MonteCarlo simulation application of the detector using the GEANT4 toolkit to evaluate the instrument performance,including the effective area, angular resolution, and energy resolution, and explored specific optimizations ofthe detector configuration. Our simulation-based analysis indicates that the current design of the VLAST isphysically feasible, with an acceptance above 10 m2 sr which is four times larger than that of the Fermi-LAT,an energy resolution better than 2% at 10 GeV, and an angular resolution better than 0.2 ◦ at 10 GeV. TheVLAST project promises to make significant contributions to the field of gamma ray astronomy and enhanceour understanding of the cosmos.
分类： 物理学 >> 核物理学 提交时间： 2024-05-23
wang ruoxu
Yuan He
shi longbo
Li chenxing
xue zongheng
jiang tiancai
xu xianbo
sun liepeng
zhang zhouli
摘要： 为验证RFQ腔体功率输入耦合器设计的合理性和减少腔体污染，设计了低损耗离线锻炼腔体，并进行了高功率试验。离线锻炼腔由两个耦合口和两个调谐器口组成。此外，耦合环的安装角度和调谐器的插入深度可以用来低腔体的功率损耗。对该离线锻炼腔体进行了电磁结构和多物理场模拟，结果表明该腔体的最小理论功率损耗为4.3%。当腔体频率变化为110kHz时，理论功率损耗增加到10%。因此，调谐器在调节过程中始终处于运动状态。多物理场模拟表明，腔体温度的升高对频率变化没有影响。当离线高功率锻炼平台建成后，测量了该系统的传输性能，功率损耗为6.3%，大于理论计算值。高功率离线锻炼采用了高效的自动扫福和驻波谐振锻炼方法。为了充分锻炼高功率输入耦合器，选择了13个驻波点。最大连续波功率大于20kW，优于预期目标。
分类： 核科学技术 >> 核科学技术其他学科 提交时间： 2024-05-22
摘要： 作为聚变反应堆候选材料，低活化铁素体钢（马氏体钢）的主要成分是Fe和Cr。在实际工况下，聚变反应产生的氦会进入材料中，产生微观缺陷，从而引起辐照损伤，影响材料的抗辐照能力（氦脆现象）及其它物理性能。本文通过第一性原理计算，模拟得出反应堆主体材料Fe-Cr合金的界面，在不同的替代位和间隙位掺杂He原子，对其结构优化后计算每种结构的形成能，得出He原子在Fe-Cr界面不同位置处的稳定性。与此同时，通过对体积的计算得出He在靠近界面的Fe八面体间隙位时会引起较大的晶格畸变，根据电子态密度分析，推断是He、Fe、Cr三种原子在特定位置相互杂化影响的结果，为下一步研究核级不锈钢微观缺陷及其物理化学性质提供理论依据。
分类： 核科学技术 >> 粒子加速器 提交时间： 2024-05-20
摘要： 电子辐照在核技术应用产业中成为重要的一部分，低能电子束在废水处理、食品保鲜等方面应用越来越广，辐照的计量参数对于辐照质量至关重要。由于低于300keV的电子束剂量学相关标准尚未建立，参数测量都溯源至10MeV电子直线加速器，测量对象的不一致带来了系统性的偏差。本论文针对低于300keV的低能电子，开展了测试与模拟计算相结合的电子束能量测量方法研究，研制了基于量热法的吸收剂量测量装置，探究了吸收剂量与束流强度、位移速度等参数的关系。结果表明：通过阶梯叠层法剂量实验结合能量沉积曲线模拟的方式实现了低能电子能量参数的测量，通过量热法实现了低能电子吸收剂量参数的测量，测量不确定度为11%（k=2）。本研究为低能电子辐照工艺提供了可靠的计量保障。
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Electromagnetic spins, including longitudinal and transverse ones, have been playing important roles in light-matter interactions. Here, we formulate a unified equation to uncover the physical origins and topological properties of longitudinal and transverse spins in a generic electromagnetic field. The equation reveals universally that the transverse spin is locked with the kinetic momentum and originated from the transverse inhomogeneities of field, whereas the helix-dependent longitudinal spin orients parallel to the local wavevector. Remarkably, a hidden extraordinary helix-dependent transverse spin possessing helix-dependent spin-momentum locking is discovered and the number of locking states consistent with the nontrivial topological spin Chern number. Furthermore, this spin which determines the inverted helical components is related to the Berry curvature closely. The findings, which are demonstrated experimentally by measuring the three-dimensional spin components in the focusing configuration, will deepen the understanding the underlying physics of spins and open an avenue for chiral quantum optical applications.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Polarization vectors of light traveling in a coiled optical fiber rotate around its propagating axis even in the absence of birefringence. This rotation was usually explained due to the Pancharatnam-Berry phase of spin-1 photons. Here, we use a purely geometric method to understand this rotation. We show that similar geometric rotations also exist for twisted light carrying orbital angular momentum (OAM). The corresponding geometric phase can be applied in photonic OAM-state-based quantum computation and quantum sensing.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Optical forces in the near fields have important applications in on-chip optical manipulations of small particles and molecules. Here, we report a study of optical force and torque on small particles induced by the optical polarization singularities of a gold cylinder. We show that the scattering of the cylinder generates both electric and magnetic C lines (i.e., lines of polarization singularities) in the near fields, and the C lines can induce complex force and torque on a dielectric/magnetic particle. The force and torque manifest dramatic spatial variations with interesting symmetry properties, providing rich degrees of freedom for near-field optical manipulations. The study, for the first time to our knowledge, uncovers the effect of optical polarization singularities on light-induced force and torque on small particles. The results contribute to the understanding of chiral light-matter interactions and can find applications in on-chip optical manipulations and optical sensing.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： How migratory birds can find the right way in navigating over thousand miles is an intriguing question, which much interested researchers in both fields of biology and physics for centuries. There several putative proposals that sound intuitively plausible all remain contested so far because those hypothesis-models of magnetoreceptor to sense geomagnetic field need either extremely high sensitivity or humankind-like intelligence to guide. Here we explore theoretically that the birds can navigate to their destination through an entirely new scenario to sense the geomagnetic field. Our proposal is based on separate peaks of the resonance-fluorescence spectrum of a four-level system derived from the ferric sulfide cluster which exists in a protein complex (Drosophila CG8198) of migratory birds. As the separation of spectral peaks contains information about geomagnetic field at both current location and birthland, the change of such separation cues the bird to choose a right direction to move and double-resonance emerges once arrived the destination. Our theoretical mechanism can explain previous experiments on the disorientation of migratory birds caused by oscillating magnetic field naturally and more precisely. This work provides insight to explain migratory navigation and motivates possible manmade practical devices.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Narrow linewidth laser(NLL) of high frequency stability and small form factor is essential to enable applications in long range sensing, quantum information and atomic clocks. Various high performance NLL have been demonstrated by Pound-Drever Hall(PDH) lock or self injection lock(SIL) of a seed laser to a vaccum-stabilized FP cavity of ultrahigh quality factor(Q). However they are often complicated lab setups due to the sophisticated stabilizing system and locking electronics. Here we report a compact NLL of 68mL volume, realized by SIL of a diode laser to a miniature FP cavity of 7.7x108 Q and 0.5mL volume, bypassing table-size vaccum, thermal and vibration isolation. We characterized the NLL with a self-delayed heterodyne system, the Lorentzian linewidth reaches 60mHz, and the integrated linewidth is ~80Hz. The frequency noise performance exceeds that of commercial NLLs and the best reported hybrid-integrated NLL realized by SIL to high Q on-chip ring resonators. Our work marks a major step toward a field-deployable NLL of superior performance utilizing ultra-high Q FP cavity.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Conventional coherent absorption occurs only when two incident beams exhibit mirror symmetry with respect to the absorbing surface, i.e., the two beams have the same incident angles, phases, and amplitudes. In this work, we propose a more general metasurface paradigm for coherent perfect absorption, with impinging waves from arbitrary asymmetric directions. By exploiting excitation of unidirectional evanescent waves, the output can be fixed at one reflection direction for any amplitude and phase of the control wave. We show theoretically and confirm experimentally that the relative amplitude of the reflected wave can be tuned continuously from zero to unity by changing the phase difference between the two beams, i.e. switching from coherent perfect absorption to full reflection. We hope that this work will open up promising possibilities for wave manipulation via evanescent waves engineering with applications in optical switches, one-side sensing, and radar cross section control.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Lingya Yu
Zengbo Wang
Lizhou Xu
Liyang Yue
Bing Yan
Igor V. Minin
Oleg V. Minin
Baidong Wu
Yiduo Chen
摘要： Photonic hook (PH) is a new type of artificial self-bending beam focused by a dielectric particle-lens with a curved waist smaller than the wavelength, which has the potential to revolutionize mesoscale photonics in many applications, e.g., optical trapping, signal switching, imaging, etc. In this paper, we discover a new mechanism that the highly curved PHs can be realised by the light interaction with the fully or partially metal-coated microchannels. The generated W-shaped and J-shaped PHs have bending angles exceeding 80-degree. Compared to other PH setups, the proposed design has a larger range to flexibly control the bending angle through the coating process and can be easily integrated with the established microfluidic systems.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： We show that the time-averaged Poynting vector in parity-time (PT ) symmetric coupled waveguides is always positive and cannot explain the stopped light at exceptional points (EPs). In order to solve this paradox, we must accept the fact that the fields E and H and the Poynting vector in non-Hermitian systems are in general complex. Based on the original definition of the instantaneous Poynting vector, a formula on the group velocity is proposed, which agrees perfectly well with that calculated directly from the dispersion curves. It explains not only the stopped light at EPs, but also the fast-light effect near it. This investigation bridges a gap between the classic electrodynamics and the non-Hermitian physics, and highlights the novelty of non-Hermitian optics.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Mode-locked lasers, which produce ultrashort pulses in the picosecond and femtosecond range, have enabled some of the most precise measurements. However, despite significant recent progress, resolving the temporal behavior of their short pulses is still a challenge. State-of-the-art oscilloscopes with tens of picosecond resolution prevent time-resolved observations in mode-locked lasers and limit the real-time pulse evolution tracking of ultrafast lasers. Here, using the time-lens technique with a Raman amplifier, we implement an ultrafast single-shot time-microscope (TM) with a high temporal magnification factor of 355 and a time measurement window of 1 millisecond that contains ~1.8*10^4 consecutive pulses. We use this TM to characterize the temporal evolution of mode-locked lasers and reveal a temporal sideway oscillation (winding) behavior, a previously unobserved feature of lasers in both theory and experiment. Our experimental observations confirm that the winding behavior is an essential feature in the operation of mode-locked lasers. We theoretically and experimentally found that the winding characteristic evolution originates from gain-induced fluctuations for relatively high gain energies, while Q-switched modulations being the main cause for lower energies. Our findings based on advanced real-time measurements open up new insights into ultrafast and transient optics and may impact future laser designs, modern ultrafast diagnostics, and influence progress in nonlinear optics in general.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Halide perovskite materials raised tremendous interest in recent years since their cheap fabrication, superior performance in both solar cell and light emitting diode (LED). Due to the existence of layered quantum well structure, quasi two-dimensional(2D) halide perovskite has more intriguing spin related physics than its 3D counterpart. For instance, the detection and brightening of dark exciton (DX) in 2D halide perovskite attracts much attention since these species can be used in opto-spintronic and quantum computing devices. Here, we report the gradually brightened emission of the DX at 2.33 eV with the thickness decreases in (PEA)2PbI4 single crystalline nanoflake, which hitherto has not been reported. By coupling with in-plane (IP) magnetic field in Voigt configuration, the DX emission can be sharply enhanced, while for the out-of-plane (OP) magnetic field in Faraday configuration, the DX emission has no noticeable change, which can be reconciled with the theory interpretation of magnetic field dependent wave function mixing between the four exciton states fi1, fi2, fi3- , fi3+. The emission of DX fi2 at 2.335 eV and the fine splitting of all the four states are observed in static PL spectroscopy for the first time. Our work thus clarifies the debating questions regarding to previous research on DX behavior in 2D halide perovskite material and sheds light on the road of realizing opto-spintronic or quantum computing devices with these materials.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Traditional lasers function using resonant cavities, in which the round-trip optical path is exactly equal to an integer multiple of the intracavity wavelengths to constructively enhance the spontaneous emission rate. By taking advantage of the enhancement from the resonant cavity, the narrowest sub-10-mHz-linewidth laser and a $10^{-16}$-fractional-frequency-stability superradiant active optical clock (AOC) have been achieved. However, a laser with atomic spontaneous radiation being destructively inhibited in an anti-resonant cavity, where the atomic resonance is exactly between two adjacent cavity resonances, has not been reported. Herein, we experimentally demonstrate inhibited stimulated emission and termed it an inhibited laser. Compared with traditional superradiant AOCs, which exhibit superiority in terms of the high suppression of cavity noise, the suppression of the cavity-pulling effect of an inhibited laser can be further improved by a factor of $(2F/pi)^2$, i.e., 2.07 in this work, which was improved from 26 to 53 times. This study will guide further development of AOCs with better stability, and thus, it is significant for quantum metrology and may lead to new research in the laser physics and cavity quantum electrodynamics fields.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： In many-cycle plane waves at intermediate intensities, the nonlinear trident process can be well-approximated by the two sequential steps of nonlinear Compton scattering of a polarised real photon followed by its transformation into an electron-positron pair via nonlinear Breit-Wheeler pair creation. We investigate this two-step process in the intermediate intensity regime by employing the locally monochromatic approximation for each step and numerically evaluating resulting expressions. When photon polarisation is included, it is found to produce an order 10% decrease in the trident rate: the importance of polarisation increases at lower intensities, and decreases at higher intensities. Its importance persists at higher intensities in a linearly-polarised background, but disappears at high intensities in a circularly-polarised background. If the two steps are made to take place in two linearly-polarised plane wave pulses with perpendicular polarisations, the pair yield can be increased by approximately 30% compared to two plane waves with the same polarisation. It is also shown that harmonic structures in the Compton step can be passed to the pair step if the Compton edge is at an energy of the order of the threshold for linear Breit-Wheeler.
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