分类: 核科学技术 >> 核探测技术与核电子学 提交时间: 2024-07-04
摘要: Cosmic-ray muons are highly penetrating background-radiation particles found in natural environments. In this study, we develop and test a plastic scintillator muon detector based on machine-learning algorithms. The detector underwent muon position-resolution tests at the Institute of Modern Physics in Lanzhou using a mul tiwire drift chamber (MWDC) experimental platform. In the simulation, the same structural and performance parameters were maintained to ensure the reliability of the simulation results. The Gaussian process regression (GPR) algorithm was used as the position-reconstruction algorithm owing to its optimal performance. The re sults of the Time Difference of Arrival algorithm were incorporated as one of the features of the GPR model to reconstruct the muon hit positions. The accuracy of the position reconstruction was evaluated by comparing the experimental results with Geant4 simulation results. In the simulation, large-area plastic scintillator detectors achieved a position resolution better than 20 mm. In the experimental-platform tests, the position resolutions of the test detectors were 27.9 mm. We also analyzed factors affecting the position resolution, including the crit ical angle of the total internal reflection of the photomultiplier tubes and distribution of muons in the MWDC. Simulations were performed to image both large objects and objects with different atomic numbers. The results showed that the system could image high- and low-Z materials in the constructed model and distinguish objects with significant density differences. This study demonstrates the feasibility of the proposed system, thereby providing a new detector system for muon-imaging applications.
分类: 物理学 >> 核物理学 提交时间: 2024-04-28
摘要: Capacitors are widely used in pulsed magnet power supplies to reduce ripple voltage, store energy, and decrease power variation. In this study, DC-link capacitors in pulsed power supplies were investigated. By deriving an analytical method for the capacitor current on the H-bridge topology side, the root-mean-square value of the capacitor current was calculated, which helps in selecting the DC-link capacitors. The proposed method solves this problem quickly and with high accuracy. The current reconstruction of the DC-link capacitor is proposed to avoid structural damage in the capacitor’s current measurement, and the capacitor’s hot spot temperature and temperature rise are calculated using the FFT transform. The test results showed that the error between the calculated and measured temperature increases was within 1.5 ◦C. Finally, the lifetime of DC-link capacitors was predicted based on Monte Carlo analysis. The proposed method can evaluate the reliability of DC-link capacitors in a non-isolated switching pulsed power supply for accelerators and is also applicable to film capacitors.
分类: 物理学 >> 交叉学科物理及相关领域的科学与技术 分类: 材料科学 >> 陶瓷学 提交时间: 2024-03-20
摘要: 高放废物固化体的长期辐照稳定性是评价其深地质处置安全性的关键指标之一。本文利用 500 keV He2+离子束辐照 2M、 3O 和 4M 型钙钛锆石陶瓷固化体, 研究高放核素长期α 衰变辐照对陶瓷结构的损伤行为。三种钙钛锆石样品通过传统高温固相法(1400 ℃, 48h两次烧结)合成。掠入射 X 射线衍射(GIXRD) 、 Raman 光谱和 XPS 研究结果发现在 α 粒子辐照下, zirconolite-2M 固化体在辐照非晶化的过程中经历了 zirconolite-2M 到 zirconolite-4M 到 pyrochlore 的结构演变; zirconolite-3O 在 5×1015 ions/cm2 剂量下部分晶体结构转变为钙钛矿,在 1×1016 ions/cm2 以上剂量快速转变为无序烧绿石; zirconolite-4M 样品在 1×1017 ions/cm2 剂量时依旧保留 zirconolite-4M 主相,次生无序烧绿石/缺陷萤石晶相。综上, 从维持晶体结构稳定性来看 zirconolite-2M 和 zirconolite-3O 的抗 α 粒子辐照能力相似,略弱于zirconolite-4M 固化体。
分类: 物理学 >> 核物理学 提交时间: 2023-09-11
摘要: Gamma-ray polarimetry is a new and prospective tool for studying various extreme high-energy celestial objects and is of great significance for the development of astrophysics. With the rapid development of microsatellite technology, the advantages in space exploration are becoming increasingly apparent. Therefore, in this paper, we conducted a simulation study on a soft gamma-ray polarimeter for a microsatellite in space. Here, we proposed a unique design structure for the polarimeter based on the microsatellite design concept and the Compton scattering principle. And then, the detailed Monte Carlo simulations using mono-energetic gamma-ray linear polarization sources and the Crab-like sources in the energy range of 0.1-10 MeV with full consideration of the orbital background were performed. The simulation results show that the polarimeter can exhibit excellent polarization detection performance. The modulation factor is 0.800.01, and the polarization angles are accurate within an error of 0.2 at 200 keV for on-axis incidence. For the Crab-like sources for on-axis incidence, the polarization degrees are consistent with the set values within the error tolerance, the modulation factor is 0.760.01, and the minimum detectable polarization reaches 2.4% at 3 for an observation time of 106 seconds. In addition, the polarimeter has recoil electron tracking, imaging, and powerful background suppression at a large field of view (2 sr). The polarimeter designed can meet the requirements of a space-soft gamma-ray polarization detector very well and has a bright research prospect.
分类: 物理学 >> 核物理学 提交时间: 2023-09-04
摘要: Steam generator tube rupture (SGTR) accident is an important scenario needed to be considered in the safety analysis of lead-based fast reactors. When the steam generator tube breaks close to the main pump, water vapor will enter the reactor core, resulting in a two-phase flow of heavy liquid metal and water vapor in fuel assemblies. The thermal-hydraulic problems caused by the SGTR accident may seriously threaten reactor cores safety performance. In this paper, the open source CFD calculation software OpenFOAM was used to encapsulate the improved Euler method into the self-developed solver LBEsteamEulerFoam. By changing different heating boundary conditions and inlet coolant types, the two-phase flow in the fuel assembly with different inlet gas content was simulated under various accident conditions. The calculation results show that the water vapor may accumulate in edge and corner channels. With the increase of inlet water vapor content, outlet coolant velocity increases gradually. When the inlet water vapor content is more than 15%, the outlet coolant temperature rises sharply with strong temperature fluctuation. When the inlet water vapor content is in the range of 5% to 20%, the upper part of the fuel assembly will gradually accumulate to form large bubbles. Compared with the VOF method, Euler method has higher computational efficiency. However, Euler method may cause an underestimation of the void fraction, so it still needs to be calibrated with future experimental data of the two-phase flow in fuel assembly.
分类: 物理学 >> 核物理学 提交时间: 2023-07-12
摘要: The in-medium feature of nuclear force which includes both nucleon-nucleon ($NN$) and hyperon-nucleon ($\Lambda N$) interactions impacts the description of single-$\Lambda$ hypernuclei. With the alternated mass number or isospin of hypernuclei, such effects could be unveiled by analyzing systematical evolution of the bulk and single-particle properties. From a density-dependent meson-nucleon/hyperon coupling perspective, a new $\Lambda N$ effective interaction in the covariant density functional (CDF) theory, namely DD-LZ1-$\Lambda1$, is obtained by fitting the experimental data of $\Lambda$ separation energies for several single-$\Lambda$ hypernuclei. It is then adopted to study the structure and transition properties of single-$\Lambda$ hypernuclei in Oxygen isotopes, comparing with several selected CDF Lagrangians. Discrepancy is observed explicitly in the isospin evolution of $\Lambda1p$ spin-orbit splitting with various effective interactions, ascribed to their divergence of the meson-hyperon coupling strengths with increasing density. In particular, the density-dependent CDFs introduce an extra contribution to enhance the isospin dependence of the splitting, which is originated from the rearrangement terms of $\Lambda$ self-energies. In addition, the characteristics of hypernuclear radii are studied along the isotopic chain. Owing to the impurity effect of $\Lambda$ hyperon, a size shrinkage is observed in the matter radii of hypernuclei as compared to their cores of normal nuclei, while its magnitude is elucidated further to correlate with the incompressibility of nuclear matter. Besides, there exists a sizable model-dependent trend that $\Lambda$ hyperon radii evolve with the neutron number, which is decided partly by the in-medium $NN$ interactions as well as the core polarization effects.
分类: 物理学 >> 核物理学 提交时间: 2023-06-24
摘要: The multinucleon transfer (MNT) reaction is one promising way to produce neutron-rich heavy nuclei and even super heavynuclei and attracts more and more attentions theoretically and experimentally. A low energy nuclear structure spectrometer calledLENSHIAF specific to the MNT reactions will be designed and constructed in the ongoing big project HIAF in China. In theLENSHIAF spectrometer, the most challenge part is how to collect and stop efficiently the high-energy MNT products into the gascell. By using Monte-Carlo method, the geometry of the gas cell, the thickness of the titanium window/degrader, and the optimalgas pressure filled in the gas cell have been calculated and estimated. For neutron-rich nuclei around N=126 from 136Xe+198Ptreaction, with a titanium window/degrader with a thickness of 2.53.5 um, a cylindrical helium gas cell with a length of 0.6 m and adiameter of 1.2 m can satisfy the requirements to stop the target-like fragments. For heavier and super heavy nuclei from 238U+238Ureaction, with a 58 um thick titanium window/degrader, the cylindrical gas cell has to be as big as a length of at least 1.6 m and adiameter of 1.6 m.
分类: 物理学 >> 核物理学 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: In this study, the activation cross-sections were measured for 232Th(n,2n)231Th reactions at neutron energies of 14.1 and 14.8 MeV, which were produced by a neutron generator through a T(d,n)4He reaction. Induced gamma-ray activities were measured using a low background gamma ray spectrometer equipped with a high resolution HPGe detector. In the cross-section calculations, corrections were made regarding the effects of gamma-ray attenuation, dead-time, fluctuation of the neutron flux, and low energy neutrons. The measured cross-sections were compared with the literature data, evaluation data (ENDF-B/VII.1, JENDL-4.0 and CENDL-3.1), and the results of the model calculation (TALYS1.6).
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: An electrostatic accelerating column was designed and fabricated by Lanzhou University for an intense D-T/D-D neutron generator. In order to achieve a neutron yield of 5.0�1012 n/s, a deuteron beam of 30 mA, accelerated to 400 kV, and transported in the electrostatic accelerating column smoothly are required. One particle-in-cell code BEAMPATH was used to simulate the beam transport, and the IONB1.0 code was used to simulate the intense beam envelopes. Emittance growths due to space charge effect and spherical aberration were analyzed. The simulation results show that the accelerating column can transport deuteron beam of 30 mA smoothly and the requirement for the neutron generator is satisfied.
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: In this paper, model-predictive control (MPC) is proposed for controlling power source of accelerators. The system state equation is employed as the predictive model. With MPC, the difference between possible output and the ideal output is forecasted and decreased, so that the system can trace the ideal trail as closely and quickly as possible. The results of simulations and experiments show that this method can reduce influence of low frequency noise.
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 digital coincidence acquisition system applied to a portable liquid scintillation counting device is developed. The system which simplifies the device design consists of a digitizer card of Agilent U1066A DC438, a discriminator and a host computer. The anode analog pulses from two photomultiplier tubes are captured by the system, which adopts the sequence acquisition storage mode. By choosing proper threshold for each channel, coincidence time window of 30 ns, and comparing the pulse amplitudes from two channels, the portable scintillation counting device can be used to detect particles. For the unquenched standard 3H sample, the results show that the detection efficiency is (58.50.1)% and the background is (86.70.7) cpm. Meanwhile, 3H spectrum is obtained.
分类: 物理学 >> 核物理学 提交时间: 2023-06-02
摘要: In this study, the rapidity distribution, collective flows, and nuclear stopping power in 197Au+197 Au collisions at intermediate energies were investigated using the ultrarelativistic quantum molecular dynamics (UrQMD) model with GEMINI++ code. The UrQMD model was adopted to simulate the dynamic evolution of heavy-ion collisions, whereas the GEMINI++ code was used to simulate the decay of primary fragments produced by UrQMD. The calculated results were compared with the INDRA and FOPI experimental data. It was found that the rapidity distribution, collective flows, and nuclear stopping power were affected to a certain extent by the decay of primary fragments, especially at lower beam energies. Furthermore, the experimental data of the collective flows and nuclear stopping power at the investigated beam energies were better reproduced when the sequential decay effect was included.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2017-03-23
摘要: The effect of isochronal annealing on vacancy-type defects in quenched FeCrNi alloys and SUS316 has been investigated by positron annihilation techniques. Vacancy-type defects gather and grow with the annealing temperature increasing to 523 K, and the vacancy-type defects annihilated gradually in FeCrNi alloys at the annealing temperature increasing. The results indicate that the addition of Mo and nonmetal elements is not the key reasons that determined the annihilated temperature of vacancy-type defects. It’s worth noting that the vacancy-type defects annihilated and dislocation-type defects formed in all sample alloys after 673 K annealing treatment. In addition, the density of defects in Mo diluted FeCrNi model alloy is lower than that in FeCrNi model alloy due to the Mo-vacancy complexes formed in Mo diluted FeCrNi model alloy. The long lifetime of vacancy-type defects in commercial stainless steel SUS316 is smaller than that in FeCrNi model alloys because the mobility of vacancy-type defects changed by nonmetal elements. In addition, vacancy-type and dislocation defects detected contribute to the S and W parameters of positron annihilation in the whole annealing treatment.