分类: 物理学 >> 核物理学 分类: 天文学 >> 天文仪器与技术 分类: 材料科学 >> 材料科学(综合) 提交时间: 2023-12-15
摘要: The GECAM series of satellites utilizes LaBr3(Ce), LaBr3(Ce,Sr), and NaI(Tl) crystals as sensitive materials for gamma-ray detectors (GRDs). To investigate the non-linearity in the detection of low-energy gamma rays and address the errors in the calibration of the E-C relationship, comprehensive tests and comparative studies of the three aforementioned crystals were conducted using Compton electrons, radioactive sources, and monoenergetic X-rays. The non-linearity test results of the Compton electrons and X-rays demonstrated substantial differences, with all three crystals presenting a higher non-linearity for X/-rays than for Compton electrons. Despite the LaBr3(Ce) and LaBr3(Ce,Sr) crystals having higher absolute light yields, they exhibited a noticeable non-linear decrease in the light yield, especially at energies below 400 keV. The NaI(Tl) crystal demonstrated an excess light output in the 6200 keV range, reaching a maximum excess of 9.2% at 30 keV in the X-ray testing and up to 15.5% at 14 keV during Compton electron testing, indicating a significant advantage in the detection of low-energy gamma rays. Furthermore, we explored the underlying causes of the observed non-linearity in these crystals. This study not only elucidates the detector responses of GECAM, but also initiates a comprehensive investigation of the non-linearity of domestically produced lanthanum bromide and sodium iodide crystals.
分类: 核科学技术 >> 核科学与技术 提交时间: 2023-12-10
摘要: X-ray photon correlation spectroscopy (XPCS) has emerged as a powerful tool for probing nanoscale dynamics of soft condensed matter and strongly correlated materials, offering high spatial resolution and high penetration capability. This technique requires high brilliance and beam coherence, which are not directly available at modern synchrotron beamlines in China. To pave the way for future XPCS experiments, we first modified the optical setup of the newly commissioned BL10U1 USAXS beamline at the Shanghai Synchrotron Radiation Facility (SSRF). Subsequently, we carried out XPCS measurements on silica suspensions of glycerol, which were opaque in appearance due to high concentrations. Image series were collected by a high frame-rate area detector. Comprehensive analysis was carried out, yielding the correlation functions and several key dynamic parameters. All results agree well with the theory of Brownian motion, demonstrating the feasibility of XPCS at SSRF. Eventually, by carefully optimizing the setup and analyzing algorithms, we achieved a time resolution of 2 ms, enabling characterization of millisecond dynamics in opaque systems.
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: 2017-11-10
摘要: Finding the electromagnetic (EM) counterpart of binary compact star merger, especially the binary neutron star (BNS) merger, is critically important for gravitational wave (GW) astronomy, osmology and fundamental physics. On Aug. 17, 2017, Advanced LIGO and Fermi/GBM independently triggered the first BNS merger, GW170817, and its high energy EM counterpart, GRB 170817A, respectively, resulting in a global observation campaign covering gamma-ray, X-ray, UV, optical, IR, radio as well as neutrinos. The High Energy X-ray telescope (HE) onboard Insight-HXMT (Hard X-ray Modulation Telescope) is the unique high-energy gamma-ray telescope that monitored the entire GW localization area and especially the optical counterpart (SSS17a/AT2017gfo) with very large collection area (~1000 cm2) and microsecond time resolution in 0.2-5 MeV. In addition, Insight-HXMT quickly implemented a Target of Opportunity (ToO) observation to scan the GW localization area for potential X-ray emission from the GW source. Although Insight-HXMT did not detect any significant high energy (0.2-5 MeV) radiation from GW170817, its observation helped to confirm the nexpected weak and soft nature of GRB 170817A. Meanwhile, Insight-HXMT/HE provides one of the most stringent constraints (~10-7 to 10-6 erg/cm2/s) for both GRB170817A and any other possible precursor or extended emissions in 0.2-5 MeV, which help us to better understand the properties of EM radiation from this BNS merger. Therefore the observation of Insight-HXMT constitutes an important chapter in the full context of multi-wavelength and multi-messenger observation of this historical GW event.