Vol.33,

Within the framework of the isospin-dependent quantum molecular dynamics model, we simulate ¹²⁹Xe + ¹¹⁹Sn collisions in an incident energy range of 20 to 190 MeV/nucleon and discuss the liquid-gas phase transition with density fluctuations. For comparison, we also extract the effective Fisher parameter τ_eff, multiplicity of intermediate-mass fragments (IMFs), and information entropy. It is found that the Fisher parameter and maximum information entropy of collisions have peak values at E_beam = 50–80 MeV/nucleon. In addition, the maximum multiplicity of IMFs has a plateau around 70 MeV/nucleon. For higher-order density moments in a larger central region of [-5,5] ³ fm³ in the collision system, a maximum plateau also appears as function of beam energy at energies exceeding 70 MeV/nucleon. These observables, which are consistent with each other, indicate a liquid-gas phase transition around 70 MeV/nucleon for the ¹²⁹Xe + ¹¹⁹Sn system.

467

Within the framework of isospin-dependent Boltzmann-Langevin model, the production cross sections of proton-rich nuclei with Z = 20-25 are investigated. According to the reaction results for different isospin of projectiles ⁴⁸Ni, ⁴⁹Ni, and ⁵⁰Ni, proton-rich fragments tend to be more easily produced in reactions with the proton-rich projectile ⁴⁸Ni. The production cross-sections of the unknown nuclei in the vicinity of the projectile are sensitive to incident energy. It is observed that incident energy of 345 MeV/u is appropriate for producing proton-rich nuclei with Z = 20-25. In projectile fragmentation reactions based on the radioactive ion beam of ⁴⁸Ni at 345 MeV/u, several unknown proton-rich nuclei near the proton drip line are generated in the simulations. All these new nuclei are near-projectile elements near Z = 28. The production cross sections of the new nuclei ³⁴Ca, ^37,38Sc, ³⁸Ti, ^40,41,42V, ^40,41Cr, and ^42,43,44,45Mn are in the range of 10^-2 – 10² mb. Hence, projectile fragmentation of radioactive ion beams of Ni is a potential method for generating new proton-rich nuclei with Z = 20-25.

744

The ultralow detection threshold, ultralow intrinsic background, and excellent energy resolution of p-type point-contact germanium detectors are important for rare-event searches, in particular for the detection of direct dark matter interactions, coherent elastic neutrino-nucleus scattering, and neutrinoless double beta decay. Anomalous bulk events with an extremely fast rise time are observed in the CDEX-1B detector. We report a method of extracting fast bulk events from bulk events using a pulse shape simulation and reconstructed source experiment signature. Calibration data and the distribution of X-rays generated by intrinsic radioactivity verified that the fast bulk experienced a single hit near the passivation layer. The performance of this germanium detector indicates that it is capable of single-hit bulk spatial resolution and thus provides a background removal technique.

455

In this study, we investigated the isospin properties of intermediate mass fragments (IMFs) for the central collisions of ^112,124Sn+^112,124Sn at a beam energy of 50 MeV per nucleon using an improved quantum molecular dynamics model (ImQMD) coupled with a sequential decay model (GEMINI). Three observables were analyzed: 1) the average center-of-mass kinetic energy per nucleon 〈Ec.m./A〉 of fragments as a function of their charge number Z; 2) the average neutron number to proton number ratio (〈N〉/Z) of fragments with a given charge number Z as a function of their center-of-mass kinetic energy per nucleon (E_c.m./A); and 3) the average total neutron number to total proton number ratio (∑N/∑Z) and double ratio (DR(N/Z)) of IMFs with Z=3-8 as a function of their center-of-mass kinetic energy per nucleon E_c.m./A. Our calculations revealed that the sensitivity of the isospin properties of IMFs relative to the stiffness of the symmetry energy remains even after sequential decay. By comparing the calculations of ∑N/∑Z and DR(N/Z) with the data, it was found that the soft symmetry energy, i.e., γ=0.5, is favored.

532

The Jiangmen Underground Neutrino Observatory (JUNO) is a multi-purpose neutrino experiment. One of the main goals is to determine the neutrino mass ordering by precisely measuring the energy spectrum of reactor antineutrinos. For the detection of reactor antineutrinos, cosmogenic backgrounds, such as ⁹Li/⁸He and fast neutrons induced by cosmic muons, should be rejected carefully by applying muon veto cuts, which require good muon track reconstruction. With a 20-kton liquid scintillator detector, the simulation shows the proportion of muon bundles (muon multiplicity ≥2) to be approximately 8% in JUNO, whereas its reconstruction has been rarely discussed in previous experiments. This study proposes an efficient algorithm for muon track reconstruction based on the charge response of a photomultiplier tube array. This is the first reconstruction of muon bundles in a large-volume liquid scintillator detector. In addition, the algorithm shows good performance and potential for reconstruction for both a single muon and double muons (muon multiplicity = 2). The spatial resolution of a single-muon reconstruction was 20 cm, and the angular resolution was 0.5°. For double-muon reconstruction, the spatial and angular resolutions could be 30 cm and 1.0°, respectively. Moreover, this paper also discusses muon classification and the veto strategy.

444

Determining the mass of plutonium metal is an important research objective in the field of nuclear material accounting and control. Based on the 3D neutron and photon transport code JMCT (Jointed Monte Carlo Transport), the gamma ray multiplicity of ²⁴⁰Pu was simulated in this study, and the average number of gamma rays leaking from ²⁴⁰Pu solid spheres with different masses was also obtained. The simulation results show that there is a one-to-one correspondence between the average number of gamma rays and the mass of ²⁴⁰Pu solid spheres in the range of 0.50∼3.00 Kg. This result provides a basis for using the average number of gamma rays to account for the mass of ²⁴⁰Pu.

552

The results of an accident analysis for the loss of offsite power (LOOP) scenario in a reference Bushehr-1 VVER-1000/V446 nuclear power plant (NPP) are presented in this paper. This study attempted to provide a better analysis of LOOP accident management by integrating deterministic and probabilistic approaches. The RELAP5 code was used to investigate the occurrence of specific thermal-hydraulic phenomena. The probabilistic safety assessment of the LOOP accident is presented using the SAPHIRE software. LOOP accident data were extracted from the Bushehr NPP final safety analysis reports and probabilistic safety analysis reports. A deterministic approach was used to reduce the core damage frequency in the probabilistic analysis of LOOP accidents. The probabilistic approach was used to better observe the philosophy of defense in depth and safety margins in the deterministic analysis of the LOOP accident. The results show that the integration of the two approaches in LOOP accident investigations improved accident control.

520

In this paper, we present a nonrecursive residual Monte Carlo method for estimating discretization errors associated with the S_N transport solution to radiation transport problems. Although this technique is general, we applied it to the mono-energetic 1-D S_N equation with linear-discontinuous finite element method spatial discretization as a demonstration of the theory for the purpose of this study. Two angular flux representations: conforming and simplified representations, were considered in this analysis, and the results were compared. It is shown that the simplified representation dramatically reduces the memory footprint and computational complexity of residual source generation and sampling while accurately capturing the error associated with certain types of responses.

436

The integrity and reliability of fuel rods under both normal and accidental operating conditions are of great importance for nuclear reactors. In this study, considering various irradiation behaviors, a fuel rod performance analysis code, named KMC-Fueltra, was developed to evaluate the thermal-mechanical performance of oxide fuel rods under both normal and transient conditions in the LMFR. The accuracy and reliability of the KMC-Fueltra were validated by analytical solutions as well as the results obtained from codes and experiments. The results indicated that KMC-Fueltra can predict the performance of oxide fuel rods under both normal and transient conditions in the LMFR.

621

Models to describe the damage and fracture behaviors of the interface between the fuel foil and cladding in UMo/Zr monolithic fuel plates were established and numerically implemented. The effects of the interfacial cohesive strength and cohesive energy on the irradiation-induced thermal-mechanical behaviors of fuel plates were investigated. The results indicated that for heterogeneously irradiated fuel plates: (1) interfacial damage and failure were predicted to be initiated near the fuel foil corner with higher fission densities, accompanied by the formation of a large gap after interface failure, which was consistent with some experimental observations; high tensile stresses in the fuel foil occurred near the edges of the failed interface, attributed to through-thickness cracking of the fuel foil, as found in some post-irradiation examinations; (2) the cohesive strength and cohesive energy of the interface both influenced the in-pile evolution behaviors of fuel plates; a lower cohesive strength or cohesive energy resulted in faster interfacial damage; (3) after interface fracture, the thickness of the whole plate increased to a greater degree (by ~20%) than that of the samples without interfacial damage, which was attributed to the locally enhanced Mises stresses and the nearby creep deformations around the cracked interface. This study provided a theoretical basis for assessing failure in fuel elements.

551

Electron spin resonance (ESR) techniques were employed to investigate the effects of the absorbed dose and post-irradiation conditions on the evolution and decay of free-radicals in cross-linked polytetrafluoroethylene (XPTFE), induced by γ-ray radiation. Chain-end free-radicals, chain alkyl free-radicals, and tertiary alkyl free-radicals were detected when XPTFE was irradiated under Ar atmosphere. The corresponding peroxy free-radicals were formed upon exposure of irradiated XPTFE to air; the free-radicals concentration first increased linearly with increasing absorbed dose, and then gradually saturated. The free-radicals yield under air atmosphere was greater than that under Ar, and the peroxy free-radicals were preserved for a relatively long time when irradiated XPTFE was stored under air atmosphere. The chain alkyl free-radicals may be converted to chain end free-radicals by β-scission, while chain end free-radicals are more sensitive to oxygen than chain alkyl free-radicals. When the annealing temperature was raised above the α-transition temperature of XPTFE, the decay of the free-radicals was greatly affected and accelerated by the motion of the molecules over the long-range.

552

Tune ripple has a significant influence on beam spill ripple in RF-knockout (RF-KO) slow extraction. In this study, a model was proposed to explain how the tune ripple affects the beam spill in RF-KO slow extraction; consequently, a simulation was performed using the lattice of the Xi'an Proton Application Facility (XiPAF) synchrotron to verify the model. The simulation demonstrates that the tune ripple influences the beam spill in two ways. On the one hand, the tune ripple causes a direct fluctuation in the separatrix area, which induces beam spill ripple. On the other hand, the tune ripple influences the emittance growth rate in RF-knockout slow extraction. These two aspects simultaneously contribute to the beam spill ripple.

619

Spatial resolution and image-processing methods for full-field X-ray fluorescence (FF-XRF) imaging using X-ray pinhole cameras were studied using Geant4 simulations with different geometries and algorithms for image reconstruction. The main objectives were: 1) calculating the quantum efficiency curves of specific cameras, 2) studying the relationships between the spatial resolution and the pinhole diameter, magnification, and camera binning value, and 3) comparing image-processing methods for pinhole camera systems. Several results were obtained using a point and plane source as the X-ray fluorescence emitter and an array of 100×100 silicon pixel detectors as the X-ray camera. The quantum efficiency of a back-illuminated deep depletion (BI-DD) structure was above 30% for the XRF energies in the 0.8–9 keV range, with the maximum of 93.7% at 4 keV. The best spatial resolution of the pinhole camera was 24.7 μm and 31.3 lp/mm when measured using the profile function of the point source, with the diameter of 20 μm, magnification of 3.16, and camera bin of 1. A blind deconvolution algorithm with Gaussian filtering performed better than the Wiener filter and Richardson iterative methods on FF-XRF images, with the signal-to-noise ratio of 7.81 dB and improved signal-to-noise ratio of 7.24 dB at the diameter of 120 μm, magnification of 1.0, and camera bin of 1.

495

An experimental picosecond time-resolved x-ray ferromagnetic resonance (TR-XFMR) apparatus with a time resolution of 13 ps (RMS) or 31 ps (FWHM) was constructed and demonstrated in the 07U and 08U1A soft X-ray beamlines at the Shanghai Synchrotron Radiation Facility (SSRF) using pump-probe detection and X-ray magnetic circular dichroism (XMCD) spectroscopy. Element- and time-resolved ferromagnetic resonance were excited by continuous microwave phase-locking of the bunch clock within the photon beam during synchrotron radiation, and were characterized by detecting the magnetic circular dichroism signals of the elements of interest in the magnetic films. Using this equipment, we measured the amplitude of the element-specific moment precession during ferromagnetic resonance (FMR) at 2 GHz in a single Ni₈₁Fe₁₉ layer.

586

China plans to develop the next generation dark matter particle explorer satellite, referred to as the Very Large Area Space Telescope (VLAST). As an essential step in this process, the prototype designing of detectors and electronics for the VLAST is currently underway. The nuclide detector is a core detector in the VLAST. It mainly measures nuclides' charges and distinguishes high-energy gamma rays and electrons. This paper will discuss the prototype readout electronics for the VLAST’s nuclide detector, which accurately measures the charge signal of the photomultiplier tubes using the VATA160 application-specific integrated circuit chip; furthermore, we consider a series of critical problems, including radiation-hardening and environment monitoring. The test results show that the system exhibits stable operation, good performance, and good technical indicators. Furthermore, each electronic channel achieves a dynamic range of 0–12.5 pC, the random noise level exceeds 1.6 fC, and the integral nonlinearity exceeds 0.35%.

421