分类: 物理学 >> 核物理学 提交时间: 2023-06-09 合作期刊: 《Nuclear Science and Techniques》
摘要: Real-time monitoring of the 14-MeV D-T fusion neutron yield is urgently required for the triton burnup study on the Experimental Advanced Superconducting Tokamak (EAST). In this study, we developed an optimal design of a fast-neutron detector based on the scintillating fiber (Sci-Fi) to provide D-T neutron yield through Geant4 simulation. The effect on the detection performance is concerned when changing the number of the Sci-Fis embedded in the probe head, minimum distance between the fibers, length of the fibers, or substrate material of the probe head. The maximum number of scintillation photons generated by the n/γ source particles and output by the light guide within an event (event: the entire simulation process for one source particle) was used to quantify the n/γ resolution of the detector as the main basis. And the intrinsic detection efficiency was used as another evaluation criterion. The results demonstrate that the optimal design scheme is to use a 5-cm probe head whose substrate material is pure aluminum, in which 463 Sci-Fis with the same length of 5 cm are embedded, and the minimum distance between the centers of the two fibers is 2 mm. The optimized detector exhibits clear directionality in the simulation, which is in line with the expectation and experimental data provided in the literature. This study presents the variation trends of the performance of the Sci-Fi detector when its main parameters change, which is beneficial for the targeted design and optimization of the Sci-Fi detector used in a specific radiation environment.
分类: 化学 >> 物理化学 提交时间: 2017-11-05 合作期刊: 《结构化学》
摘要: A new lanthanide formate oxalate framework [Eu(C2O4)(HCOO)]n (1) has been synthesized via hydrothermal method and characterized by single-crystal X-ray diffraction (SC-XRD). The framework crystallizes in the orthorhombic Pnma space group, with a = 7.0984(4), b = 6.6442(3), c = 10.6793(6) Å, V = 503.68(4) Å3, Z = 3, C3HO6Eu, Mr = 285.00 g/mol, Dc = 3.7581 g/cm3, F(000) = 520.3796, μ = 12.413 mm-1, the final R = 0.0264 and wR = 0.0628 for 797 observed reflections with I > 2σ(I). The photoluminescence (PL) measurements reveal the significant red emission of the framework is dominated by the (5D0 → 7F2) electronic transition at 614 nm. Further variable-temperature powder X-ray diffraction (VT-PXRD) indicates that framework 1 shows slight negative thermal expansion (NTE) along the a-axis, and positive thermal expansion (PTE) along the b and c axes.
分类: 物理学 >> 核物理学 分类: 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间: 2024-01-10
摘要: Traditional particle identification methods are time consuming, experience-dependent, and poor repeatability challenges in heavy-ion collisions at low and intermediate energies. Researchers urgently need solutions to the dilemma of traditional particle identification methods. This study explores the possibility of applying intelligent learning algorithms to the particle identification of heavy-ion collisions at low and intermediate energies. Multiple intelligence algorithms, including XgBoost and TabNet, were selected to test datasets from the neutron ion multi-detector for reaction-oriented dynamics (NIMRODISiS) and Geant4 simulation. Machine learning algorithms based on tree structures and deep learning algorithms e.g. TabNet show excellent performance and generalization ability. Adding additional data features besides energy deposition can improve the algorithm's identification ability when the data distribution is nonuniform. Intelligent learning algorithms can be applied to solve the particle identification problem in heavy-ion collisions at low and intermediate energies.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: We study the parity-symmetry-breaking quantum phase transition (QPT) in a cavity magnonic system driven by a parametric field, where the magnons in a ferrimagnetic yttrium-iron-garnet sphere strongly couple to a microwave cavity. With appropriate parameters, this cavity magnonic system can exhibit a rich phase diagram, including the parity-symmetric phase, parity-symmetry-broken phase, and bistable phase. When increasing the drive strength beyond a critical threshold, the cavity magnonic system undergoes either a first- or second-order nonequilibrium QPT from the parity-symmetric phase with microscopic excitations to the parity-symmetry-broken phase with macroscopic excitations, depending on the parameters of the system. Our work provides an alternate way to engineer the QPT in a hybrid quantum system containing the spin ensemble in a ferri- or ferromagnetic material with strong exchange interactions.
分类: 物理学 >> 核物理学 提交时间: 2023-06-20
摘要: The ratio of the number of emitted pions from the target side to that from the projectile side at target rapiditywithin the reaction plane is investigated for the study of the pion dynamics with an isospin-dependent quantummolecular dynamic model. The results show that high-energy pions are emitted preferentially towards the targetside and, therefore, they are freezed out at the early stage of the collision. By contrast, low-energy pionsare emitted predominantly in the opposite direction, which means that they are emitted in later stage. Thisarguement is based on the shadowing effect caused by the interaction of pions with the spectator matter inperipheral collisions at target or projectile rapidities. This phenomenon disappears in the central collision or atmidrapidity due to the weaker shadowing effect. The calculated ratios are also compared with the experimentaldata.
分类: 物理学 >> 核物理学 提交时间: 2023-09-13
摘要: Abstract: In this experimental study, involving deuteriumdeuterium fusion neutron emission spectroscopy (NES) measurement on the experimental advanced superconducting tokamak (EAST), a liquid scintillator detector (BC501A) was employed. This decision was based on the detector's superior sensitivity, optimal time-response, and its exceptional n- discrimination capability. This detector emits fast pulse signals that are as narrow as 100 ns, with high count rates that can peak at several Mcps. However, conventional nuclear circuits faced challenges in performing pulse height analysis, n pulse shape discrimination (PSD), and in recording the entire pulse waveform under such high-count-rate conditions. To address these challenges, a high-speed digital pulse signal acquisition and processing system was designed. The system was developed around a micro-telecommunications computing architecture (MTCA). Within this structure, a signal acquisition and processing (SAQP) module communicated through PCI Express (PCIe) links, achieving a bandwidth of up to 1.6 GB/s. To accurately capture the detailed shape of the pulses, four channels of analog-to-digital converters (ADCs) were used, each with a 500-MSPS sampling rate and a 14-bit resolution, ensuring an accuracy that surpassed 11 bits. An n- discrimination algorithm, based on the two-gate integral method, was also developed. Implemented within field programmable gate arrays (FPGA), this algorithm provided a real-time n- discrimination spectrum for pulse height analysis. The system underwent rigorous testing in a laboratory setting and during an EAST experiment. The results confirmed that the innovative SAQP system can satisfy the demanding requirements of high-parameter experiments, manage count rates of up to 2 Mcps, execute real-time n- discrimination algorithms, and record entire pulse waveforms without any data loss.
分类: 核科学技术 >> 核探测技术与核电子学 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: A nuclear spectrum generator for semiconductor X-ray detectors is designed in this paper. It outputs step ramp signals with random distribution in amplitude and time according to specified reference spectrum. The signals are similar to the signals from an actual semiconductor X-ray detector, and can be use to check spectrum response characteristics of an X-ray fluorometer. This helps improving energy resolution of the X-ray fluorometer. The spectrum generator outputs step ramp signals satisfying the probability density distribution function of any given reference spectrum in amplitude through sampling on the basis of 32-bit randomizer. The system splits 1024 interval segmentation of the time that the step ramp signals appear, and calculates the appearance probability of step ramp signals in different intervals and the average time between the time intervals, by random sampling. The step ramp signals can meet the rule of exponential distribution in time. Test results of the spectrum generator show that the system noise is less than 2.43 mV, the output step ramp signals meet the Poisson distribution in counting rate and the probability density distribution function of the reference spectrum in amplitude. The counting rate of the output step ramp signals can be adjusted. It meets the rule of the output signals from semiconductor X-ray detectors, such as Si-pin detector and silicon drift detector.
分类: 物理学 >> 核物理学 分类: 核科学技术 >> 核科学与技术 分类: 核科学技术 >> 核探测技术与核电子学 提交时间: 2024-01-08
摘要: To detect radioactive substances with low activity levels, an anticoincidence detector and a high-purity germanium (HPGe) detector are typically used simultaneously to suppress Compton scattering background, thereby resulting in an extremely low detection limit and improving the measurement accuracy. However, the complex and expensive hardware required does not facilitate the application or promotion of this method. Thus, a method is proposed in this study to discriminate the digital waveform of pulse signals output using an HPGe detector, whereby Compton scattering background is suppressed and a low minimum detectable activity (MDA) is achieved without using an expensive and complex anticoincidence detector and device. The electric-field-strength and energy-deposition distributions of the detector are simulated to determine the relationship between pulse shape and energy-deposition location, as well as the characteristics of energy-deposition distributions for full- and partial-energy deposition events. This relationship is used to develop a pulse-shape-discrimination algorithm based on an artificial neural network for pulse-feature identification. To accurately determine the relationship between the deposited energy of gamma rays in the detector and the deposition location, we extract four shape parameters from the pulse signals output by the detector. Machine learning is used to input the four shape parameters into the detector. Subsequently, the pulse signals are identified and classified to discriminate between partial- and full-energy deposition events. Some partial-energy deposition events are removed to suppress Compton scattering. The proposed method effectively decreases the MDA of an HPGe -energy dispersive spectrometer. Test results show that the Compton suppression factors for energy spectra obtained from measurements on 152Eu, 137Cs, and 60Co radioactive sources are 1.13 (344 keV), 1.11 (662 keV), and 1.08 (1332 keV), respectively, and that the corresponding MDAs are 1.4%, 5.3%, and 21.6% lower, respectively
分类: 物理学 >> 核物理学 提交时间: 2023-12-07
摘要: To detect radioactive substances with a low activity level, an anti-coincidence detector and high-purity germanium detector (HPGe) are often used in combination to suppress the Compton scattering background, thereby obtaining an extremely low detection limit and improving the measurement accuracy. However, the complex and expensive hardware system required does not facilitate application and promotion of this method. Thus, a method is proposed to discriminate the digital waveform of pulse signals output by a HPGe detector, whereby the Compton scattering background is suppressed and a low minimum detectable activity (MDA) is obtained without using an expensive and complex anti-coincidence detector and device. The electric field strength distribution and the energy deposition distribution in the detector are simulated to determine the relationship between the pulse shape and location of energy deposition, as well as the characteristics of the energy deposition distribution for full- and partial-energy deposition events. This relationship is used to develop a pulse shape discrimination (PSD) algorithm based on employing an artificial neural network (ANN) for pulse feature identification. To accurately determine the relationship between the deposited energy of gamma (g)-rays in the detector and deposition location, we extract four shape parameters from the pulse signals output by the detector. Machine learning is used to input the four shape parameters to the detector. Then, the pulse signals are identified and classified to discriminate between partial- and full-energy deposition events, and some partial-energy deposition events are removed to suppress Compton scattering. The proposed method effectively lowers the MDA of a HPGe -energy dispersive spectrometer. Test results show that the Compton suppression factors for energy spectra obtained from measurements on 152Eu, 137Cs and 60Co radioactive sources are 1.13 (344 keV), 1.11 (662 keV) and 1.08 (1332 keV), respectively, and the corresponding MDAs are lowered by 1.4%, 5.3% and 21.6%.
分类: 物理学 >> 核物理学 提交时间: 2024-07-30
摘要: In current neural network algorithms for nuclide identification in high-background, poor-resolution detectors,traditional network paradigms including back-propagation networks, convolutional neural networks, recurrentneural networks, etc. have been limited in research on γ spectrum analysis because of their inherent mathemat#2;ical mechanisms. It is difficult to make progress in terms of training data requirements and prediction accuracy.In contrast to traditional network paradigms, network models based on the transformer structure have the charac#2;teristics of parallel computing, position encoding, and deep stacking, which have enabled good performance innatural language processing tasks in recent years. Therefore, in this paper, a transformer-based neural network(TBNN) model is proposed to achieve nuclide identification for the first time. First, the Geant4 program wasused to generate the basic single-nuclide energy spectrum through Monte Carlo simulations. A multi-nuclideenergy spectrum database was established for neural network training using random matrices of γ-ray energy,activity, and noise. Based on the encoder-decoder structure, a network topology based on the transformer wasbuilt, transforming the 1024-channel energy spectrum data into a 32 × 32 energy spectrum sequence as themodel input. Through experiments and adjustments of model parameters, including the learning rate of theTBNN model, number of attention heads, and number of network stacking layers, the overall recognition ratereached 98.7%. Additionally, this database was used for training AI models such as back-propagation networks,convolutional neural networks, residual networks, and long short-term memory neural networks, with overallrecognition rates of 92.8%, 95.3%, 96.3%, and 96.6%, respectively. This indicates that the TBNN model exhib#2;ited better nuclide identification among these AI models, providing an important reference and theoretical basisfor the practical application of transformers in the qualitative and quantitative analysis of the γ spectrum.
分类: 核科学技术 >> 核仪器、仪表 提交时间: 2023-06-01
摘要: 核安全防护通常需要同时探测中子和伽马射线,探测器的实时中子/伽马脉冲分辨是其关键性能参数。近年来,采用Cs2LiLaBr6 (CLLB)晶体的双读出探测器引起了广泛关注,论文研究电荷比较法、幅度比较法、时间比较法和脉冲梯度法的甄别性能,以及Sallen-Key滤波器的甄别效果。实验结果表明,通过合适的滤波,四种方法的品质因数(FOM)都有所提高。其中,电荷比较法抗噪声性能最佳,最适合CLLB探测器实时甄别中子/伽马脉冲。其甄别性能取决于参数、和。在对应脉冲峰值10%的时刻,,仅需延迟640-740 ns,此刻对应3.1-3.3 MeV的电荷比较方法最优FOM大于1.46。所提出的最大分辨差模型( MDDM)计算值与最优FOM的差异小于3.9%,表明该模型可以很好地指导电荷比较法的参数选择。
分类: 核科学技术 >> 粒子加速器 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: The multi-bunch injection adopted at Shanghai Synchrotron Radiation Facility (SSRF) increases the injection rate greatly, with much less injection time than that of single bunch injection. It reduces massively the beam failure time during users operation and prolongs the pulsed injection hardware lifetime. In this paper, the scheme to produce multi bunches for the RF electron gun is described. The filling result and beam orbit stability for top up operation is discussed.
提交时间: 2017-05-02
摘要: principles calculations. The obtained phonon frequencies agree well with the measurements of Raman scattering. The thermodynamic properties are calculated within quasi-harmonic approximation, and the measured lattice thermal conductivity is well reproduce
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: SnCdxTe materials were synthesized by the zone-melting method for this thermoelectric performance study. The X-ray diffraction results show that the lattice parameter decreases with increasing x, following Vegard's law of rock-salt structure SnTe and CdTe. Besides, the room temperature Seebeck coefficients of the SnCdxTe system are enhanced to >60 mV K 1, larger than those of Cd-doped SnTe synthesized by spark plasma sintering. A large power factor of 25 mW cm 1 K 1 is achieved in SnCd0.12Te at 820 K, which rivals those of high performance PbTe-based materials. As a result, the highest ZT of 1.03 at 820 K was achieved for SnCd0.12Te.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: We study type I clathrate Ba8Cu5.1Ge40.2Sn0.7 single crystals (space group Pm3"n, no. 223, a 1⁄4 10.7151(3)) grown using a Sn flux method. Microprobe analysis and single-crystal X-ray diffraction reveal a small amount of Sn embedded in the Cu/Ge framework, which increases disorder at the guest Ba sites. Ba8Cu5.1Ge40.2Sn0.7 is diamagnetic with a susceptibility of 2.8 10 7 emu g 1 and shows metal-like behavior (dr/dT > 0) with a low charge carrier concentration of 0.5 e per unit cell at 300 K. The single crystals show a relatively high carrier mobility (m (300 K) 1⁄4 11.9 cm2 V 1) and very low lattice thermal conductivity (0.6 W m 1 K 1). The thermoelectric figure of merit ZT of Ba8Cu5.1Ge40.2Sn0.7 single crystals reaches a maximum value of 0.6 at 773 K, which can be further improved by adjusting the chemical composition.
提交时间: 2017-05-02
摘要: Heterovalent Sn2O3 nanosheets were fabricated via an oxidation annealing process and the formation mechanism was investigated. The temperature required to complete the phase transformation from Sn3O4 to Sn2O3 was considered. Two contrasting experiments sh
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Tin selenide (SnSe) compound has attracted much attention due to its unprecedented high ZT (B2.6) in single crystals. The polycrystalline SnSe materials were then prepared to improve the mechanical performance for large-scaled application. However, the ZT values of 0.3–0.8 were much lower due to their poor electrical properties. In the present study, the zone melting method is employed to prepare the polycrystalline SnSe samples, which show highly textured structures and strong anisotropic thermoelectric performance. A maximum power factor (S2s) of 9.8 mW cm 1 K 2 was obtained in the polycrystalline samples, which is comparable with that of SnSe single crystals, resulting in a peak ZT of 0.92 at 873 K. The zone-melted ingot was then pulverized into powders and the bulk material was prepared by the spark plasma sintering (SPS) technique. As a result, the ZT value was enhanced to be over 1.0, owing to the slight reduction of lattice thermal conductivity and maintenance of electrical performance. The present investigation indicates that the TE performance of the SnSe compound can be significantly improved by the texture modulation.