Vol.30,

Nano-structures/patterns formed by biomolecules can produce different physicochemical properties in terms of hydrophobicity, zeta-potential, color, etc., which play paramount roles in life. Peptides, as the main bio-building blocks, can form nanostructures with different functions, either in solutions or on interfaces. Previously, we synthesized a short peptide with the inspiration of an Alzheimer’s disease (AD) related peptide: amyloid β peptide (A-β), namely GAV-9, which can epitaxially self-assemble into regular nanofilaments on liquid–solid interfaces, and it was found that both the hydrophobicity and charge state of the interfaces can significantly influence its assembling behavior. It was also reported that another A-β contained dipeptide, FF, can self-assemble into nanostructures in solutions. Owing to the close relationship between these two short peptides, it is interesting to conjugate them into a de novo peptide with two separated structural domains and study its self-assembling behavior. To this end, herein we have synthesized the GAV-FF peptide with a sequence of NH₂-VGGAVVAGVFF-CONH₂, and verified its self-assembling property using the in situ liquid phase atomic force microscopy (AFM). The results show that the GAV-FF peptide can self-assemble into nanofilaments both in solutions and on aqueous–solid interfaces, but with different morphologies. The FF domain accelerates the template-assisted self-assembling (TASA) process of the GAV domain, which in return enhances the solubility of FF in aqueous solutions and further participates in the fibrillization of FF. The current results could help deepen the understanding of the aggregation mechanism of disease-related peptides, and could also shed light on the strategies to create artificial bio-functional nanostructures/patterns, which hold a significant potential for biomedical applications.

407

Muon scattering tomography is believed to be a promising technique for cargo container inspection owing to the ability of natural muons to penetrate into dense materials and the absence of artificial radiation. In this work, the material discrimination ability of muon scattering tomography is evaluated based on experiments at the Tsinghua University cosmic ray muon tomography (TUMUTY) facility, with four materials: flour (as drugs substitute), aluminum, steel, and lead. The features of the different materials could be discriminated with cluster analysis and classifiers based on support vector machine (SVM). The overall discrimination precisions for these four materials could reach 70, 95, and 99% with 1-, 5-, and 10-min-long measurement, respectively.

353

Using molecular dynamics simulations, we investigate the influence of Na and Cl ions on the evaporation of nanoscale water on graphene oxide surfaces. As the concentration of NaCl increases from 0 to 1.5 M, the evaporation rate shows a higher decrease on patterned graphene oxide than that on homogeneous graphene oxide. The analysis shows an obvious decrease in the evaporation rate from unoxidized regions, which can be attributed to the increased amount of Na⁺ ions near the contact lines. The proximity of Na⁺ significantly extends the H-bond lifetime of the outermost water molecules, which reduces the number of water molecules diffusing from the oxidized to unoxidized regions. Moreover, the effect of the ions on water evaporation is less significant when the oxidation degree varies in a certain range. Our findings advance the understanding of the evaporation process in the presence of ions, and highlights the potential application of graphene oxide in achieving controllable evaporation of liquids.

403

The ¹²C+¹²C fusion reaction is famous because of its complication of molecular resonances, and it plays an important role in both nuclear structural research and astrophysics. It is extremely difficult to measure the cross-sections of ¹²C+¹²C fusions at energies of astrophysical relevance because of the very low reaction yields. To measure the complicated resonant structure that exists in this important reaction, an efficient thick target method has been developed and applied for the first time at energies E_c.m. lt;5.3 MeV. A scan of the cross-sections over a relatively wide range of energies can be carried out using only a single beam energy. The result of measurement at E_c.m.= 4.1 MeV is compared with results from previous work. This method will be useful for searching for potentially existing resonances of ¹²C+¹²C in the energy range 1 MeV lt; E_c.m. lt;3 MeV.

465

PrFeB magnets, which possess excellent magnetic properties at low temperatures, have important application value as cryogenic permanent magnet undulators for synchrotron radiation sources and free electron lasers. In this research study, several high-performance PrFeB magnets (P42H, P48SH, and P48UH) were prepared, and their performance was comprehensively examined, including evaluations of their magnetic properties, microstructures, uniformity, and stability. Next, their application prospects were analyzed and discussed. In China, the first cryogenic permanent magnet undulators (CPMU) with P48SH magnets with 18 mm cycle lengths have been developed. When the temperature is 80 K and the gap is 6.0 mm, the magnetic field measurement results of the CPMU showed that the effective magnetic field peak was approximately 0.92 T, yielding an increase of 11.76 % relative to operation at 300 K, with an RMS phase error of about 4.99°.

379

The silicon photomultiplier (SiPM) with epitaxial quenching resistor (EQR) is an emerging and developing technology that has recently attracted the interest from the research community. It has characteristics of a continuous low-resistance cap layer and integrated quenching resisters in epitaxial silicon layer, which makes it possible to increase microcell density or reduce microcell size, thus obtain large dynamic range and high photon detection efficiency (PDE) simultaneously. Results published show that the EQR SiPM with N-on-P diode configuration had relatively low PDE at peak wavelength of 480nm as 16%. This paper reported the EQR SiPM with P-on-N diode configuration having active area of 3×3 mm² and cell density of 10000/mm² (total 90000 pixels). It was characterized with gain of 2E5, dark count rate of 7 MHz, crosstalk of 7%, dynamic range of 85000 pixels, overall recovery time of 32 ns at room temperature and over-voltage of 3.5 V. The improved PDE at peak wavelength of 420nm was 30%.

442

In this paper, we present an ultrafast digitizer utilizing the DRS4 switched capacitor array application-specific integrated circuit to achieve an ultrafast sampling speed of at most 5 GS/s. We cascaded all eight channels (sub-channels) of a single DRS4 chip for increased storage depth. The digitizer contains four DRS4 chips, a quad-channel analog-to-digital converter, a controlling field-programmable gate array, a PXI interface, and an SFP+ connector. Consequently, each DRS4 channel has a depth of 8192 points and a vertical resolution of 14 bits. The readout sequences should be broken into several segments and then reordered to obtain the correct sequential data sets, and this offline procedure varies in different readout modes. This paper describes the design and implementation of the hardware; in particular, the respective processing procedures are described in detail. Furthermore, the offset error is calibrated and corrected to improve the precision of the captured waveform in both single-channel and high-resolution modes.

483

An experimental muon source (EMuS) will be built at the China Spallation Neutron Source (CSNS). In Phase-I of CSNS, it has been decided that EMuS will provide a proton beam of 5 kW and 1.6 GeV to generate muon beams. A 128-channel muon spin rotation/relaxation/resonance (μSR) spectrometer is proposed as a prototype surface muon spectrometer in a sub-branch of EMuS. The prototype spectrometer includes a detection system, sample environment, and supporting mechanics. The current design has two rings located at the forward and backward directions of the muon spin with 64 detectors per ring. The simulation shows that the highest asymmetry of approximately 0.28 is achieved by utilizing two 10-mm-thick brass degraders. To obtain the optimal asymmetry, the two-ring structure is updated to a four-ring structure with 32 segments in each ring. An asymmetry of 0.42 is obtained through the simulation, which is higher than that of all the current μSR spectrometers in the world.

635

Real-time track reconstruction in high energy physics experiments at colliders running at high luminosity is very challenging for trigger systems. To perform pattern recognition and track fitting, artificial retina or Hough transformation algorithms have been introduced to the field typically implemented on state-of-the-art field-programmable gate array (FPGA) devices. In this paper we report on two FPGA implementations of the retina algorithm: one using a mixed Floating-Point core and the other using Fixed-Point and Look-Up Table, and detailed measurements of the retina performance are investigated and compared. So far, the retina has mainly been used in a detector configuration comprising parallel planes, and the goal of our work is to study the hardware implementation of the retina algorithm and estimate the possibility of using such a method in a real experiment.

416

A spaceborne hard X-ray spectrometer, composed of an array of 99 scintillation detectors and associated readout electronics, has been developed for the hard X-ray imager (HXI). The HXI is one of the three payloads onboard the Advanced Space-based Solar Observatory (ASO-S), which is scheduled to be launched in early 2022 as the first Chinese solar satellite. LaBr₃ scintillators and photomultiplier tubes with a super bialkali cathode are used to achieve an energy resolution better than 20% at 30 keV. Further, a new multi-channel charge-sensitive readout application-specific integrated circuit guarantees high-frequency data acquisition with low power consumption. This paper presents a detailed design of the spectrometer for the engineering model of the HXI, and discusses its noise and linearity performance.

471

Multiple analytical methods and Monte Carlo simulations were performed to evaluate neutron penetration in straight and curved labyrinths. Factors studied included variations in beam losses of off-axis point source, on-axis point source, and line source. For the straight labyrinth, it was found that the analytical expressions neglect the dose rate platform appearing at the bend of the labyrinth, and the agreement between analytical methods and Monte Carlo estimation was related to the type of neutron source term. For the curved labyrinth, the neutron attenuation length obtained under different conditions was nearly identical, and appeared to be in quite good accord with the empirical formula calculation. Moreover, the neutron energy spectra along the centerline distance of the labyrinth were also analyzed. In the first leg, differences in beam loss led to variance in the distribution of spectra, while in the second and subsequent legs, the spectra were similar, where the main contributors were thermal neutrons. This work is valuable for practical design of the labyrinths in the accelerator facilities.

422

The solid-fuel thorium molten salt reactor (TMSR-SF1) is a 10-MWth fluoride-cooled pebble bed reactor. As a new reactor concept, one of the major limiting factors to reactor lifetime is radiation-induced material damage. The fast neutron flux (E > 0.1 MeV) can be used to assess possible radiation damage. Hence, a method for calculating high-resolution fast neutron flux distribution of the full-scale TMSR-SF1 reactor is required. In this study, a two-step subsection approach based on MCNP5 involving a global variance reduction (GVR) method, referred to as forward-weighted consistent adjoint driven importance sampling (FW-CADIS), was implemented to provide fast neutron flux distribution throughout the TMSR-SF1 facility. In addition, instead of using the general source specification cards, the user-provided SOURCE subroutine in MCNP5 source code was employed to implement a source biasing technique specialized for TMSR-SF1. In contrast to the one-step analog approach, the two-step subsection approach eliminates zero-scored mesh tally cells and obtains tally results with extremely uniform and low relative uncertainties. Furthermore, the maximum fast neutron fluxes of the main components in TMSR-SF1 are provided, which can be used for radiation damage assessment of the structural materials.

403

There is an obvious effort to increase the burn up of used fuel assemblies in order to improve fuel utilization. A more effective operation can be realized by extending the fuel cycles or by increasing the number of reloadings. This change is nevertheless connected with increasing the uranium enrichment even above 5% of ²³⁵U. Burnable absorbers are widely used to compensate for the positive reactivity of fresh fuel. With proper optimization, burnable absorbers decrease the reactivity excess at the beginning of the cycle, and they can help with stabilization of power distribution. This paper describes properties of several materials that can be used as burnable absorbers. The change in concentration or position of the pin with a burnable absorber in a fuel assembly was analyzed by the HELIOS transport lattice code. The multiplication factor and power peaking factor dependence on fuel burn up were used to evaluate the neutronic properties of burnable absorbers. The following four different materials are discussed in this paper: Gd₂O₃, IFBA, Er₂O₃, and Dy₂O₃. Gadolinium had the greatest influence on fuel characteristics. The number of pins with a burnable absorber was limited in the VVER-440 fuel assembly to six. In the VVER-1000 fuel assembly, 36 pins with a burnable absorber can be used as the assembly is larger. The erbium depletion rate was comparable with uranium burn up. Dysprosium had the largest parasitic absorption after depletion.

606

In fast reactors, the inherent neutron source strength is often insufficient for monitoring the reactor startup operation with ex-core detectors. To increase the subcritical neutron flux, an auxiliary neutron source subassembly (SSA) is generally used to overcome this problem. In this study, the estimated neutron source strength and detector count rate of an antimony–beryllium-based SSA are obtained using the deterministic transport code DORT and Monte Carlo calculations. Because the antimony activation rate is a critical parameter, its sensitivity to the capture cross section and neutron flux spectrum are studied. The reaction cross section sensitivity is studied by considering data from different evaluated nuclear data files. It is observed that, because of the variation in the cross sections from different evaluated nuclear data files, the values of the saturation gamma (>1.67MeV) activity and neutron strength predicted by ORIGEN2 lie within +2%. The obtained antimony activation rate and sensitivity to the neutron flux are partially validated by irradiating samples of antimony in the KAMINI reactor. The average one-group capture cross sections of bare and cadmium-covered ¹²³Sb samples obtained by the ratio method are 4.0 and 1.78b, respectively. The results of the calculation predicting the activated neutron source strength as a function of operating time and sensitivity to the neutron spectrum in the irradiation region are also presented.

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