Vol.33,

Muon tomography is a novel method for the non-destructive imaging of materials based on muon rays, which are highly penetrating in natural background radiation. Currently, the most commonly used imaging methods include muon radiography and muon tomography. A previously studied method known as coinciding muon trajectory density tomography, which utilizes muonic secondary particles, is proposed to image low and medium atomic number (Z) materials. However, scattering tomography is mostly used to image high-Z materials, and coinciding muon trajectory density tomography exhibits a hollow phenomenon in the imaging results owing to the self-absorption effect. To address the shortcomings of the individual imaging methods, hybrid model tomography combining scattering tomography and coinciding muon trajectory density tomography is proposed and verified. In addition, the peak signal-to-noise ratio was introduced to quantitatively analyze the image quality. Different imaging models were simulated using the Geant4 toolkit to confirm the advantages of this innovative method. The simulation results showed that hybrid model tomography can image centimeter-scale materials with low, medium, and high Z simultaneously. For high-Z materials with similar atomic numbers, this method can clearly distinguish those with apparent differences in density. According to the peak signal-to-noise ratio of the analysis, the reconstructed image quality of the new method was significantly higher than that of the individual imaging methods. This study provides a reliable approach to the compatibility of scattering tomography and coinciding muon trajectory density tomography.

448

Experimental techniques based on SR facilities have emerged with the development of synchrotron radiation (SR) sources. Accordingly, detector miniaturization has become significant for the development of SR experimental techniques. In this study, the miniaturization of a detector was achieved by coupling a commercial silicon PIN photodiode (SPPD) into a beamstop, aiming for it not only to acquire X-ray absorption fine structure (XAFS) spectra, but also to protect the subsequent two-dimensional detector from high-brilliance X-ray radiation damage in certain combination techniques. This mini SPPD detector coupled to a beamstop was used as the rear detector in both the conventional sampling scheme and novel high-frequency (HF) sampling scheme to collect the transmission XAFS spectra. Traditional ion chambers were also used to collect the transmission XAFS spectra, which were used as the reference. These XAFS spectra were quantitatively analyzed and compared; the results demonstrated that the XAFS spectra collected by this SPPD in both the conventional sampling scheme and HF sampling scheme are feasible. This study provides a new detector-selection scheme for the acquisition of the quick-scanning XAFS (QXAFS) and HF sampling XAFS spectra. The SPPD detector presented in this study can partially meet the requirements of detector miniaturization.

483

As modern accelerator technologies advance toward more compact sizes, conventional invasive diagnostic methods of cavity detuning introduce negligible interference in measurements and run the risk of harming structural surfaces. To overcome these difficulties, this study developed a non-invasive diagnostic method using knowledge of scattering parameters with a convolutional neural network and the interior point method. Meticulous construction and training of the neural network led to remarkable results on three typical acceleration structures: a 13-cell S-band standing-wave linac, a 12-cell X-band traveling-wave linac, and a 3-cell X-band RF gun. The trained networks significantly reduced the burden of the tuning process, freed researchers from tedious tuning tasks, and provided a new perspective for the tuning of side-coupling, semi-enclosed, and total-enclosed structures.

411

There is an urgent need for high-quality and high-frequency clock generators for high-energy physics experiments. The transmission data rate exceeds 10 Gbps for a single channel in future readout electronics of silicon pixel detectors. Others, such as time measurement detectors, require a high time resolution based on the time-to-digital readout architecture. A phase-locked loop (PLL) is an essential and broadly used circuit in these applications. This study presents an application-specific integrated circuit of a low-jitter, low-power LC-tank that is PLL fabricated using 55-nm CMOS technology. It includes a 3rd-order frequency synthesis loop with a programmable bandwidth, a divide-by-2 pre-scaler, standard low-voltage differential signaling interfaces, and a current mode logic (CML) driver for clock transmissions. All the d-flip-flop dividers and phase-frequency detectors are protected from single-event upsets using the triple modular redundancy technique. The proposed VCO uses low-pass filters to suppress the noise from bias circuits. The tested LC-PLL covers a frequency locking range between 4.74 GHz to 5.92 GHz with two subbands. The jitter measurements of the frequency-halved clock (2.56 GHz) are less than 460 fs and 0.8 ps for the random and deterministic jitters, respectively, and a total of 7.5 ps peak-to-peak with a bit error rate of 10^-12. The random and total jitter values for frequencies of 426 MHz and 20 MHz are less than 1.8 ps and 65 ps, respectively. The LC-PLL consumed 27 mW for the core and 73.8 mW in total. The measured results nearly coincided with the simulations and validated the analyses and tests.

675

A transition edge sensor (TES) is extremely sensitive to changes in temperature, and combined with a high-Z metal of a certain thickness, it can realize high-energy resolution measurements of particles such as X-rays. X-rays with energies below 10 keV have a weak penetrating ability; hence, only gold or bismuth of a few micrometers in thickness can guarantee a quantum efficiency higher than 70%. Therefore, the entire structure of the TES X-ray detector in this energy range can be realized using a microfabrication process. However, for X-rays or γ-rays from 10 keV to 200 keV, submillimeter absorber layers are required, which cannot be realized using the microfabrication process. This paper first briefly introduces a set of TES X-ray detectors and their auxiliary systems, and then focuses on the introduction of the TES γ-ray detector with an absorber based on a submillimeter lead–tin alloy sphere. The detector achieved a quantum efficiency above 70% near 100 keV and an energy resolution of approximately 161.5 eV at 59.5 keV.

427

P-i-n Al_xGa_1-xAs/GaAs detectors with graded compositions and graded doping were grown and prepared. From the current–voltage and capacitance–voltage measurement results, the devices had good p–n junction diode characteristics, and the electric field strength under an unbiased voltage was 1.7 × 10⁵ Vcm^-1. The full width at half maximum and charge collection efficiency of the detectors obtained from energy spectrum measurements of 5.48-MeV alpha particles were 3.04 and approximately 93%, respectively. In this study, we created the most advanced and promising state-of-the-art unbiased detector reported to date.

414

The small-angle neutron scattering (SANS) instrument, one of the first three instruments of the China Spallation Neutron Source (CSNS), is designed to probe the microscopic and mesoscopic structures of materials in the scale range 1 to100 nm. A large-area ³He tube array detector has been constructed and operates at the CSNS SANS instrument since August 2018. It consists of 120 linear position-sensitive detector tubes, each 1 m in length and 8 mm in diameter, and filled with ³He gas at 20 bar to obtain a high detection efficiency. The ³He tubes were divided into ten modules, providing an overall area of 1000 mm × 1020 mm with a high count rate capability. Because each tube is installed independently, the detector can be quickly repaired in situ by replacing damaged tubes. To reduce air scattering, the SANS detector must operate in a vacuum environment (0.1 mbar). An all-metal sealing technique was adopted to avoid high-voltage breakdown by ensuring a high-voltage connection and an electronic system working in an atmospheric environment. A position resolution of 7.8±0.1 mm (full width at maximum) is measured along the length of the tubes, with a high detection efficiency of 81±2 % at 2 Å. Operating over the past four years, the detector appears to perform well and with a high stability, which supports the SANS instrument to finish approximately 200 user scientific programs.

636

The precise vertex reconstruction for large-liquid scintillator detectors is essential. A novel machine-learning-based method was successfully developed to reconstruct an event vertex in JUNO. In this study, the performance of machine-learning-based vertex reconstruction was further improved by optimizing the input images of neural networks. By separating the information of different types of PMTs and adding the information of the second hit of PMTs, the vertex resolution was improved by approximately 9.4 % at 1 MeV and 9.8 % at 11 MeV.

519

A new type of neutron detector based on monocrystalline Si is developed to measure the fluence and flux density of thermal and fast neutrons. The principle of this detector is based on the relationship between changes in electrical conductivity and neutron fluence during irradiation. Therefore, the absolute values of thermal neutron fluence and flux density are measured in a facile manner with high reliability. Compared with activation methods, our method not only possesses a similar accuracy, but also demonstrates superior application potential for the investigation of neutron fields in nuclear reactors owing to its suitable half-life.

420

For a more systematic understanding of the levels of environmental tritium and its behavior in East Asia, a database on environmental tritium was established based on the literature published in the past 30 years. Subsequently, the levels and behavior of the environmental tritium were further studied by statistical analyses. The results indicate that the distribution of environmental tritium is inhomogeneous and complex. In areas without nuclear facilities, the level of environmental tritium has decreased to its background level, even though a certain number of atmospheric nuclear tests were performed before 1980. In general, the level of atmospheric tritium was marginally higher than the levels in precipitation and surface water; the levels in shallow groundwater and seawater were considerably lower. Furthermore, the levels of tritium in the atmosphere, precipitation, and inland surface water were strongly correlated with latitude and distance from the coastline. In soil and living organisms, the level of tissue-free water tritium (TFWT) was comparable to the tritium levels in local rainfall, whereas persistence of organically bound tritium (OBT) in the majority of organisms resulted in an OBT/TFWT ratio greater than one. Conversely, extremely high levels of environmental tritium were observed near certain nuclear power plants and the Fukushima accident sites. These results highlight the requirement to know the tritium baseline level and its behavior in the environment beforehand to better assess the impact of tritium discharge. Further investigations of environmental tritium in East Asia using more efficient and adequate monitoring methods are also required.

492

The Shanghai Laser Electron Gamma Source (SLEGS) is a powerful gamma source that provides MeV gamma-ray beams for nuclear science and technology. It was developed as one of the 16 beamline stations in the Phase II Project of the Shanghai Synchrotron Radiation Facility (SSRF). The slant-scattering mode is for the first time systematically employed in laser Compton scattering (LCS) at SLEGS to produce energy-tunable quasi-monoenergetic gamma-ray beams. The SLEGS officially completed its commissioning from July to December 2021. Gamma rays in the energy range of 0.25 - 21.7 MeV with a flux of 2.1 × 10⁴ - 1.2 × 10⁷ photons/s and an energy spread of 2 – 15 % were produced during the test. This paper reports the results from commissioning the SLEGS beamline.

548

Muon radiography is a promising technique for imaging the internal density structures of targets such as tunnels, pyramids, and volcanoes up to a scale of a few hundred meters by measuring the flux attenuation of cosmic ray muons after they have travelled through these targets. In this study, we conducted experimental muon radiography of one of the volcanoes in the Wudalianchi area in Northeast China to image its internal density structure. The muon detector used in this study was composed of plastic scintillators and silicon photomultipliers. After approximately one and a half months of observing the crater and conduit of the Laoheishan volcano cone in Wudalianchi from September 23^rd to November 10^th 2019, more than 3 million muon tracks fulfilling the data selection criteria were collected. Based on the muon samples and high-resolution topography obtained through aerial photogrammetry using an unmanned aerial vehicle, a density image of the Laoheishan volcano cone was constructed. The results obtained in this experiment demonstrate the feasibility of using a radiography technique based on plastic scintillator detectors. To obtain the density distribution, we performed a detailed background analysis and found that low-energy charged particles dominated the background noise. Relatively higher densities were found near the surface of the volcanic cone, whereas relatively lower densities were found near the center of the volcanic cone. The experiment in this study is the first volcano muon tomography study performed in China. Our work provides an important reference for future research.

405

The deuteron breakup on heavy targets has been investigated in the framework of an improved quantum molecular dynamics model, focusing on the production of neutrons near zero degrees. The experimental differential cross-sections of neutron production in the 102 MeV d+C reactions were reproduced by simulations. Based on the consistency between the model prediction and experiment, the feasibility of producing a neutron beam through the breakup of deuteron on a carbon target was demonstrated. Because of the nucleon Fermi motion inside the deuteron, the energy spectrum of the inclusive neutron near 0° in the laboratory exhibits considerable energy broadening in the main peak, whereas the long tail on the low-energy side is suppressed. By coincidentally measuring the accompanying deuteron breakup proton, the energy of the neutron can be tagged with an intrinsic uncertainty of approximately 5% (1σ). The tagging efficiency of the accompanying proton on the forward-emitted neutron can reach 90%, which ensures that the differential cross-section in the (d, np) channel remains two orders higher than that in (p,n) after considering the measurement of accompanying protons. This enables the application of a well-defined energy neutron beam in an event-by-event scheme.

381

Polytetrafluoroethylene (PTFE) is a low-background polymer that is applied to several applications in rare-event detection and underground low-background experiments. PTFE-based electronic substrates are important for reducing the detection limit of high-purity germanium detectors and scintillator calorimeters, which are widely applied in dark matter and 0υββ detection experiments. The traditional adhesive bonding method between PTFE and copper is not conducive to working in liquid nitrogen and extremely low-temperature environments. To avoid adhesive bonding, PTFE must be processed for surface metallization owing to the mismatch between the PTFE and copper conductive layer. Low-background PTFE matrix composites (m-PTFE) were selected to improve the electrical and mechanical properties of PTFE by introducing SiO₂/TiO₂ particles. The microstructures, surface elements, and electrical properties of PTFE and m-PTFE were characterized and analyzed following ion implantation. PTFE and m-PTFE surfaces were found to be broken, degraded, and crosslinked by ion implantation, resulting in C=C conjugated double bonds, increased surface energy, and increased surface roughness. Comparably, the surface roughness, bond strength, and conjugated double bonds of m-PTFE were significantly more intense than those of PTFE. Moreover, the interface bonding theory between PTFE and the metal copper foil was analyzed using the direct metallization principle. Therefore, the peel strength of the optimized electronic substrates was higher than that of the industrial standard at extremely low temperatures, while maintaining excellent electrical properties.

663