Abstract：The 232Th(n,f) cross-section is very important in basic nuclear physics and applications based on the Th/U fuel cycle. Using the time-of-flight method and a multi-cell fast fission ionization chamber, a novel measurement of the 232Th(n,f) cross-section relative to 235U in the 1–200 MeV range was performed at the China Spallation Neutron Source Back-n white neutron source (Back-n). The fission event-neutron energy spectra of 232Th and 235U fission cells were measured in the single-bunch mode. Corrected 232Th/235U fission cross-section ratios were obtained, and the measurement uncertainties were 2.5–3.7% for energies in the 2–20 MeV range and 3.6–6.2% for energies in the 20–200 MeV range. The 232Th(n,f) cross-section was obtained by introducing the standard cross-section of 235U(n,f). The results were compared with those of previous theoretical calculations, measurements, and evaluations. The measured 232Th fission cross-section agreed with the main evaluation results in terms of the experimental uncertainty, and 232Th fission resonances were observed in the 1–3 MeV range. The present results provide 232Th(n,f) cross-section data for the evaluation and design of Th/U cycle nuclear systems.
Abstract：The nuclear charge radius plays a vital role in determining the equation of state of isospin asymmetric nuclear matter. Based on the correlation between the differences in charge radii of mirror-partner nuclei and the slope parameter (L) of symmetry energy at the nuclear saturation density, an analysis of the calibrated slope parameter L was performed in finite nuclei. In this study, relativistic and non-relativistic energy density functionals were employed to constrain the nuclear symmetry energy through the available databases of the mirror-pair nuclei 36Ca-36S, 38Ca-38Ar, and 54Ni-54Fe. The deduced nuclear symmetry energy was located in the range 29.89–31.85 MeV, and L of the symmetry energy essentially covered the range 22.50–51.55 MeV at the saturation density. Moreover, the extracted Ls at the sensitivity density was located in the interval range 30.52–39.76 MeV.
Abstract：Radio-frequency (RF) breakdown analysis and location are critical for successful development of high-gradient traveling-wave (TW) accelerators, especially those expected to generate high-intensity, high-power beams. Compared with commonly used schemes involving dedicated devices or complicated techniques, a convenient approach for breakdown locating based on transmission line (TL) theory offers advantages in the typical constant-gradient TW-accelerating structure. To deliver such an approach, an equivalent TL model has been constructed to equate the TW-accelerating structure based on the fundamental theory of the TL transient response in the time domain. An equivalence relationship between the TW-accelerating structure and the TL model has been established via analytical derivations associated with grid charts and verified by TL circuit simulations. Furthermore, to validate the proposed fault-locating method in practical applications, an elaborate analysis via such a method has been conducted for the recoverable RF-breakdown phenomena observed at an existing prototype of a TW-accelerating-structure-based beam injector constructed at the Huazhong University of Science and Technology. In addition, further considerations and discussion for extending the applications of the proposed method have been given. This breakdown-locating approach involving the transient response in the framework of TL theory can be a conceivable supplement to existing methods, facilitating solution to construction problems at an affordable cost.
Abstract：Neutron computed tomography (NCT) is widely used as a noninvasive measurement technique in nuclear engineering, thermal hydraulics, and cultural heritage. The neutron source intensity of NCT is usually low and the scan time is long, resulting in a projection image containing severe noise. To reduce the scanning time and increase the image reconstruction quality, an effective reconstruction algorithm must be selected. In CT image reconstruction, the reconstruction algorithms used can be divided into three categories: analytical algorithms, iterative algorithms, and deep learning. Because the analytical algorithm requires complete projection data, it is not suitable for reconstruction in harsh environments, such as strong radiation, high temperature, and high pressure. Deep learning requires large amounts of data and complex models, which cannot be easily deployed, as well as has a high computational complexity and poor interpretability. Therefore, this paper proposes the OS-SART-PDTV iterative algorithm, which uses the ordered subset simultaneous algebraic reconstruction technique (OS-SART) algorithm to reconstruct the image and the first-order primal-dual algorithm to solve the total variation (PDTV), for sparse-view NCT three-dimensional reconstruction. The novel algorithm was compared with other algorithms (FBP, OS-SART-TV, OS-SART-AwTV, and OS-SART-FGPTV) by simulating the experimental data and actual neutron projection experiments. The reconstruction results demonstrate that the proposed algorithm outperforms the FBP, OS-SART-TV, OS-SART-AwTV, and OS-SART-FGPTV algorithms in terms of preserving edge structure, denoising, and suppressing artifacts.
Abstract：With the advancement in X-ray astronomical detection technology, various celestial polarization detection projects have been initiated. To meet the calibration requirements of polarimeters on the ground, a polarized X-ray radiation facility was designed for this study. The design was based on the principle that X-rays incident at 45° on a crystal produce polarized X-rays, and a second crystal was used to measure the polarization of the X-rays produced by the facility after rotation. The effects of different diaphragm sizes on the degree of polarization were compared, and the facility produced X-rays with polarization degrees of up to 99.55±0.96% using LiF200 and LiF220 crystals. This result revealed that the polarization of incident X-rays is one of the factors affecting the diffraction efficiency of crystals. The replacement of different crystals can satisfy the calibration requirements of polarized X-ray detectors with more energy points in the energy range (4–10) keV. In the future, the facility should be placed in a vacuum environment to meet the calibration requirements at lower energies.
Abstract：The in-core self-powered neutron detector (SPND) acts as a key measuring device for the monitoring of parameters and evaluation of the operating conditions of nuclear reactors. Prompt detection and tolerance of faulty SPNDs are indispensable for reliable reactor management. To completely extract the correlated state information of SPNDs, we constructed a twin model based on a generalized regression neural network (GRNN) that represents the common relationships among overall signals. Faulty SPNDs were determined because of the functional concordance of the twin model and real monitoring systems, which calculated the error probability distribution between the model outputs and real values. Fault detection follows a tolerance phase to reinforce the stability of the twin model in the case of massive failures. A weighted K-nearest neighbor model was employed to reasonably reconstruct the values of the faulty signals and guarantee data purity. The experimental evaluation of the proposed method showed promising results, with excellent output consistency and high detection accuracy for both single- and multiple-point faulty SPNDs. For unexpected excessive failures, the proposed tolerance approach can efficiently repair fault behaviors and enhance the prediction performance of the twin model.