Subjects: Physics >> Nuclear Physics submitted time 2023-06-18 Cooperative journals: 《Nuclear Science and Techniques》
Abstract: Isospin-dependent Quantum Molecular Dynamics model (IQMD) has been applied to investigate the Pygmy Dipole Resonance (PDR) and Giant Dipole Resonance (GDR) in Ni isotopes by Coulomb excitation. By Gaussian fitting to the photon emission spectra, the peak energies and strengths of PDR and GDR are extracted. Their sensitivities to impact parameter, incident energy and the symmetry energy are discussed. By the comparison of energy-weighted sum rule (EWSR) with the data and other calculations for 68Ni, the parameters of density-dependence of symmetry energy in the IQMD are constrained. In addition, the N/Z dependence of PDR and GDR parameters of Ni isotopes are investigated, and the results that the EWSR increases linearly with the N/Z are obtained.
Subjects: Geosciences >> Hydrology submitted time 2022-03-24 Cooperative journals: 《干旱区科学》
Abstract:Abstract: Qinghai Lake is the largest saline lake in China. The change in the lake volume is an indicator of the variation in water resources and their response to climate change on the Qinghai-Tibetan Plateau (QTP) in China. The present study quantitatively evaluated the effects of climate change and land use/cover change (LUCC) on the lake volume of the Qinghai Lake in China from 1958 to 2018, which is crucial for water resources management in the Qinghai Lake Basin. To explore the effects of climate change and LUCC on the Qinghai Lake volume, we analyzed the lake level observation data and multi-period land use/land cover (LULC) data by using an improved lake volume estimation method and Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) model. Our results showed that the lake level decreased at the rate of 0.08 m/a from 1958 to 2004 and increased at the rate of 0.16 m/a from 2004 to 2018. The lake volume decreased by 105.40108 m3 from 1958 to 2004, with the rate of 2.24108 m3/a, whereas it increased by 74.02108 m3 from 2004 to 2018, with the rate of 4.66108 m3/a. Further, the climate of the Qinghai Lake Basin changed from warm-dry to warm-humid. From 1958 to 2018, the increase in precipitation and the decrease in evaporation controlled the change of the lake volume, which were the main climatic factors affecting the lake volume change. From 1977 to 2018, the measured water yield showed an increase-decrease-increase fluctuation in the Qinghai Lake Basin. The effects of climate change and LUCC on the measured water yield were obviously different. From 1977 to 2018, the contribution rate of LUCC was 0.76% and that of climate change was 100.76%; the corresponding rates were 8.57% and 91.43% from 1977 to 2004, respectively, and 4.25% and 104.25% from 2004 to 2018, respectively. Quantitative analysis of the effects and contribution rates of climate change and LUCC on the Qinghai Lake volume revealed the scientific significance of climate change and LUCC, as well as their individual and combined effects in the Qinghai Lake Basin and on the QTP. This study can contribute to the water resources management and regional sustainable development of the Qinghai Lake Basin.
Subjects: Physics >> Nuclear Physics submitted time 2024-04-28
Abstract: The Shanghai Laser Electron Gamma Source (SLEGS, located in BL03SSID) beamline at the Shanghai Synchrotron Radiation Facility (SSRF) is a laser Compton scattering (LCS) gamma source used for the investigation of nuclear structure, which is in extensive demand in fields such as nuclear astrophysics, nuclear cluster structure, polarization physics, and nuclear energy. The beamline is based on the inverse Compton scattering of 10640 nm photons on 3.5 GeV electrons and a gamma source with variable energy by changing the scattering angle from 20° to 160°. γ-rays of 0.25–21.1 MeV can be extracted by the scheme consisting of the interaction chamber, coarse collimator, fine collimator, and attenuator. The maximum photon flux for 180° is approximately 10^7 photons/s at the target at 21.7 MeV, with a 3-mm diameter beam. The beamline was equipped with four types of spectrometers for experiments in (γ,γ’), (γ,n), and (γ,p α). At present, nuclear resonance fluorescence (NRF) spectrometry, flat efficiency neutron detector (FED) spectrometry, neutron time-of-flight (TOF) spectrometry, and light-charged particle (LCP) spectrometry methods have been developed.
Subjects: Physics >> Nuclear Physics submitted time 2024-02-16
Abstract: The Shanghai Laser Electron Gamma Source(SLEGS) has delivered a quasi-monochromatic, continuously energy-tunable gamma-ray beam. Based on the photon activation analysis(PAA) method, SLEGS has built and developed a photon activation analysis platform, including online activation and offline low-background HPGe detector measurement systems, as an alternative to direct measurement methods and a cross-tests at low throughput. Due to the short half-lives spanning from minutes to days and characteristics such as ease of fabrication, cost-effectiveness, and stability, gold (197Au) and zinc (64Zn) emerge as favorable activation targets in the gamma-ray beam flux monitor. Notably, their utility shows a multitude of advantages in monitoring the gamma-ray beam flux typically 105 photons/s with the energy of 13.16 to 19.08 MeV under the condition of the 3 mm coarse collimator. Especially in high-flux $\gamma$-ray beam experiments can be well applied.
Peer Review Status:Awaiting Review
Subjects: Physics >> Nuclear Physics submitted time 2024-02-28
Abstract: Shanghai Laser Electron Gamma Source (SLEGS) is a quasi-monoenergetic, and energy-tunable MeV gamma-rays source generated by the inverse Laser Compton Scattering (LCS) of lasers and electrons. SLEGS is the only LCS gamma source in the world with a continuously variable collision angular range. The gamma activation analysis is one of the effective methods to study the properties of materials. This paper introduces the gamma activation platform of SLEGS, including the online activation experiment, the low background offline measurement, and the energy and efficiency calibration for the high purity germanium (HPGe) detector. The counting rate of the shielded HPGe has been controlled down to 5.2 cps/s within 60 keV-3 MeV region under the current low background environment. The activation platform of the SLEGS has provided favorable conditions for gamma activation measurements, which will play an important role in future research in the fields of nuclear physics, nuclear astrophysics, medical applications, materials science, and environmental science.
Subjects: Physics >> Nuclear Physics Subjects: Physics >> Interdisciplinary Physics and Related Areas of Science and Technology submitted time 2023-06-20
Abstract: The Shanghai laser electron gamma source (SLEGS) is a powerful tool for exploring photonuclear physics, such as giant dipole resonance (GDR) and pygmy dipole resonance, which are the main mechanisms of collective nuclear motion. The goal of the SLEGS neutron time-of-fight (TOF) spectrometer is to measure GDR and specifc nuclear structures in the energy region above the neutron threshold. The SLEGS TOF spectrometer was designed to hold 20 sets of EJ301 and LaBr3 detectors. Geant4 was used to simulate the efciency of each detector and the entire spectrometer, which provides a reference for the selection of detectors and layout of the SLEGS TOF spectrometer. Under the events of 208Pb, implementations of coincidence and time-of-fight technology for complex experiments are available; thus, y and neutron decay events can be separated. The performance of SLEGS TOF spectrometer was systematically evaluated using ofine experiments, in which the time resolution reached approximately 0.9 ns.