按提交时间
按主题分类
按作者
按机构
  • Method for rapid warning and activity concentration estimates in online water γ-spectrometry systems

    分类: 物理学 >> 核物理学 提交时间: 2024-01-03

    摘要: Online γ-spectrometry systems for inland waters, most of which extract samples in situ and in real time, are able to produce reliable activity concentration measurements for waterborne radionuclides only when they are distributed relatively uniformly and enter into a steady-state (SS) diffusion regime in the measurement chamber. To protect residents’ health and ensure the safety of the living environment, better timeliness is required for this measurement method. To address this issue, this study established a mathematical model of the online water γ-spectrometry system so that rapid warning and activity estimates can be obtained for water under non-steady-state (NSS) conditions. In addition, the detection efficiency of the detector for radionuclides during the NSS diffusion process was determined by applying the computational fluid dynamics (CFD) technique in conjunction with Monte Carlo simulations. On this basis, a method was developed that allowed the online water -spectrometry system to provide rapid warning and activity concentration estimates for radionuclides in water. Subsequent analysis of the NSS-mode measurements of 40K radioactive solutions with different activity concentrations determined the optimum warning threshold and measurement time for producing accurate activity concentration estimates for radionuclides. The experimental results show that the proposed NSS measurement method is able to give warning and yield accurate activity concentration estimates for radionuclides 55.42 and 69.42 min after the entry of a 10 Bq/L 40K radioactive solution into the measurement chamber, respectively. These times are much shorter than the 90 min required by the conventional measurement method. Furthermore, the NSS measurement method allows the measurement system to give rapid (within approximately 15 min) warning when the activity concentrations of some radionuclides reach their respective limits stipulated in the Guidelines for Drinking-water Quality of the WHO, suggesting that this method considerably enhances the warning capacity of in situ online water γ-spectrometry systems.

  • Temperature-Dependent Group Delay of Photonic-Bandgap Hollow-Core Fiber Tuned by Surface-Mode Coupling

    分类: 光学 >> 量子光学 提交时间: 2023-02-19

    摘要: Surface modes (SM) are highly spatially localized modes existing at the core-cladding interface of photonic-bandgap hollow-core fiber (PBG-HCF). When coupling with SM, the air modes (AM) in the core would suffer a higher loss despite being spectrally within the cladding photonic bandgap, and would be highly dispersive around the avoided crossing (anti-crossing) wavelength. In this paper, we numerically demonstrate that such avoided crossings can play an important role in the tuning of the temperature dependence of group delay of AM of PBG-HCF. At higher temperatures, both the thermal-optic effect and thermal expansion contribute to the redshift of avoided crossing wavelength, giving rise to a temperature dependence of the AM dispersion. Numerical simulations show that the redshift of avoided crossing can significantly tune the thermal coefficient of delay (TCD) of PBG-HCF from -400 ps/km/K to 400 ps/km/K, approximately -120 ppm/K to 120 ppm/K. In comparison with the known tuning mechanism by the thermal-induced redshift of photonic bandgap [Fokoua et al., Optica 4, 659, 2017], the tuning of TCD by SM coupling presents a much broader tuning range and higher efficiency. Our finding would provide a new route to design PBG-HCF for propagation time sensitive applications.

  • Simulation study of BESIII with stitched CMOS pixel detector using ACTS

    分类: 物理学 >> 核物理学 提交时间: 2023-12-13

    摘要: The reconstruction of the tracks of charged particles with high precision is crucial for HEP experiments to
    achieve their physics goals. The BESIII drift chamber, which is used as the tracking detector of the BESIII
    experiment, has suffered from aging effects resulting in degraded tracking performance after operation for ap-
    proximately 15 years. To preserve and enhance the tracking performance of BESIII, one of the proposals is to
    add one layer of a thin cylindrical CMOS pixel sensor based on state-of-the-art stitching technology between
    the beam pipe and the drift chamber. The improvement in the tracking performance of BESIII with such an
    additional pixel detector compared to that with only the existing drift chamber was studied using the modern
    common tracking software ACTS , which provides a set of detector-agnostic and highly performant tracking
    algorithms that h

  • Measurements of $^{160}$Dy($p,\gamma$) at energies relevant for astrophysical $\gamma$ process

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Rare information on photodisintegration reactions of nuclei with mass numbers $A \approx 160$ at astrophysical conditions impedes our understanding of the origin of $p$-nuclei. Experimental determination of the key ($p,\gamma$) cross sections has been playing an important role to verify nuclear reaction models and to provide rates of relevant ($\gamma,p$) reactions in $\gamma$-process. In this paper we report the first cross section measurements of $^{160}$Dy($p,\gamma$)$^{161}$Ho and $^{161}$Dy($p,n$)$^{161}$Ho in the beam energy range of 3.4 - 7.0 MeV, partially covering the Gamow window. Such determinations are possible by using two targets with various isotopic fractions. The cross section data can put a strong constraint on the nuclear level densities and gamma strength functions for $A \approx$ 160 in the Hauser-Feshbach statistical model. Furthermore, we find the best parameters for TALYS that reproduce the A $\thicksim$ 160 data available, $^{160}$Dy($p,\gamma$)$^{161}$Ho and $^{162}$Er($p,\gamma$)$^{163}$Tm, and recommend the constrained $^{161}$Ho($\gamma,p$)$^{160}$Dy reaction rates over a wide temperature range for $\gamma$-process network calculations. Although the determined $^{161}$Ho($\gamma$, p) stellar reaction rates at the temperature of 1 to 2 GK can differ by up to one order of magnitude from the NON-SMOKER predictions, it has a minor effect on the yields of $^{160}$Dy and accordingly the $p$-nuclei, $^{156,158}$Dy. A sensitivity study confirms that the cross section of $^{160}$Dy($p$, $\gamma$)$^{161}$Ho is measured precisely enough to predict yields of $p$-nuclei in the $\gamma$-process.

  • Model Independent Approach of the JUNO $^8$B Solar Neutrino Program

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: The physics potential of detecting $^8$B solar neutrinos is exploited at the Jiangmen Underground Neutrino Observatory (JUNO), in a model independent manner by using three distinct channels of the charged-current (CC), neutral-current (NC) and elastic scattering (ES) interactions. Due to the largest-ever mass of $^{13}$C nuclei in the liquid-scintillator detectors and the potential low background level, $^8$B solar neutrinos would be observable in the CC and NC interactions on $^{13}$C for the first time. By virtue of optimized event selections and muon veto strategies, backgrounds from the accidental coincidence, muon-induced isotopes, and external backgrounds can be greatly suppressed. Excellent signal-to-background ratios can be achieved in the CC, NC and ES channels to guarantee the $^8$B solar neutrino observation. From the sensitivity studies performed in this work, we show that one can reach the precision levels of 5%, 8% and 20% for the $^8$B neutrino flux, $\sin^2\theta_{12}$, and $\Delta m^2_{21}$, respectively, using ten years of JUNO data. It would be unique and helpful to probe the details of both solar physics and neutrino physics. In addition, when combined with SNO, the world-best precision of 3% is expected for the $^8$B neutrino flux measurement.