Vol.26,

424

The BL14W1 beamline at Shanghai Synchrotron Radiation Facility (SSRF) is an X-ray absorption fine-structure (XAFS) beamline, for investigating atomic local structure, which is demanded extensively in the fields of physics, chemistry, materials science, environmental science and so on. The beamline is based on a 38-pole wiggler with the maximum magnetic field of 1.2 T. X-rays of 4.5–40 keV can be extracted by the optical scheme consisting of white beam vertical collimating mirror, liquid-nitrogen-cooled double crystal monochromator of Si(111) and Si(311), toroidal focusing mirror and higher harmonics rejection mirror. The maximum photon flux about 5×10¹² photons/s at the sample at 10 keV, with a beam size of 0.3 mm×0.3 mm. The beamline is equipped with four types of detectors for experiments in either transmission or fluorescence mode. At present, quick-XAFS, grazing incidence XAFS, X-ray emission spectroscopy, high-pressure XAFS and time-resolved X-ray excited optical luminescence methods have been developed.

598

High brightness γ-rays produced by laser Compton scattering (LCS) are ideal probes for the study of nucleon and nuclear structure. We propose such a γ-ray source using the backscattering of a laser from the bright electron beam produced by the linac of the Shanghai Soft X-ray Free-electron Laser (SXFEL) test facility at the Shanghai Institute of Applied Physics (SINAP). The performance is optimized through theoretical analysis and benchmarked with 4D Monte-Carlo simulations. The peak brightness of the source is expected to be larger than 2×10²² photons/(mm² mrad² s 0.1%BW) and photon energy ranges from 3.7 MeV to 38.9 MeV. Its performance, compared to Extreme Light Infrastructure-Nuclear Physics (ELI-NP), and the Shanghai Laser-Electron Gamma-ray Source (SLEGS), is given. The potential for basic and applied research is also briefly outlined.

452

401

A direct incident fluence measurement method based on amorphous silicon electronic portal imaging device (a-Si EPID) has been developed for pretreatment verification of intensity-modulated radiation therapy (IMRT). The EPID-based incident fluence conversion method deconvolves EPID images to the primary response distribution based on measured lateral scatter kernels in the EPID detector using Conjugate Gradient algorithm. The primary response is converted to the incident fluence based on measured fluence conversion matrix which corrects for off-axis position dependence of the a-Si EPID response and the "horn" beam profile caused by flatting filter. To verify feasibility and accuracy of this method, square fields of various sizes and two IMRT plans were delivered. The dose distributions computed based on EPID-derived incident fluence were compared with the measurement data. For all square field sizes except the smallest field (2 cm), the mean dose differences in cross-line dose profiles were within 1% excluding the penumbra region, and gamma passing percentages with a 2%/2 mm criterion were about 99%. For two IMRT plans, the least gamma passing percentage for all eight IMRT fields was 98.14% with 2%/3 mm criteria. It can be concluded that our direct EPID-based incident fluence conversion method is accurate and capable of being applied to pretreatment dose verification in clinical routines.

385

The gel dosimeter has the uniquely capacity in recording radiation dose distribution in three dimensions (3D), which has the specific advantages in dosimetry measurements where steep dose gradients exist. In this study, a novel radiochromic gel dosimeter was developed by dispersing nanovesicles self-assembled by 10, 12-pentacosadiynoic acid (PCDA) into the tissue equivalence gel matrix. The characteristics of radiochromic PCDA vesicle gel dosimeters were evaluated. Results indicate that these radiochromic gel dosimeters have good linear response to 1.7 MeV electron beam irradiation in the dose range of 0.32–6.36 kGy. In addition, the radiochromic gel dosimeters overcome the limitations of the existing gel dosimeters such as diffusion effect, post-radiation effect, and poor forming ability. Hence, the radiochromic PCDA vesicle gel dosimeters developed could be generally applied to 3D dose distribution measurement with optical readout.

468

Diffusion behaviors of Se(IV) and Re(VII) in bentonite were investigated by a through-diffusion method in nitrate, sulfate, carbonate and silicate solutions. SEM-EDS analysis showed that Se(IV) was reduced to red precipitate Se(0) by sulfite. Se(IV) was sorbed on bentonite with distribution coefficient K_d of (2.6–5.3)×10^-4 m³/kg in sulfite, nitrate and sulfate solutions, whereas it was hardly sorbed in carbonate and silicate solutions. The effective diffusion coefficients were D_e= (0.81–7.0)×10^-11 m²/s for Se(IV) and D_e= (1.4–4.4)×10^-11 m²/s for Re(VII). The D_e value of Se(IV) exhibited a dependence on the inorganic salts in the order of sulfite ≈ nitrate ≈ sulfate > silicate > carbonate, whereas the salts had insignificant effect on Re(VII) diffusion. The results suggest that the discrepancy in diffusion mechanism may lead to the different impact of the salts on the diffusion of Se(IV) and Re(VII) in GMZ bentonite.

385

Understanding uranium-protein interaction is important for revealing the mechanism of uranyl ion (UO₂²⁺) toxicity. In this study, we investigated the interaction between UO₂²⁺ and a quadruple mutant of cytochrome b₅ (E44/48/56A/D60A cyt b₅, namely 4A cyt b₅) by spectroscopic approaches. The four mutated negatively-charged surface residues of cyt b₅ have been considered to be the interactive sites with cytochrome c (cyt c). Also, we studied the interaction between UO₂²⁺ and the protein-protein complex of 4A cyt b₅-cyt c. The results were compared to the interaction between UO₂²⁺ and cyt b₅, and the interaction between cyt c and cyt b₅-cyt c complex, from previous studies. It was found that the interaction of UO₂²⁺-cyt b₅, i.e., uranyl ion binding to cyt b₅ surface at Glu37 and Glu43 as previously proposed by molecular modeling, is regulated by both surface mutations of cyt b₅ and its interacting protein partner cyt c. These provide valuable information on metal-protein-protein interactions and clues for understanding the mechanism of uranyl toxicity.

346

As a potential matrix of three-dimensional gel dosimeter, agarose hydrogels will be used for measuring radiation doses, hence the importance of studying their radiation resistance and radiolysis mechanism. Physical property and chemical structure of physically cross-linked agarose hydrogel samples irradiated to 0–200 kGy by ⁶⁰Co γ-rays were analyzed by universal testing machine, gel permeation chromatography, fourier transform infrared spectrometer, ultraviolet visible spectroscopy, nuclear magnetic resonance, and gas chromatography. The results showed that agarose hydrogels had good radiation stability below 25 kGy, and the maximum compression strength of sample was ca. 0.1 MPa at 25 kGy. The irradiated samples degraded obviously and liquefied gradually with increasing doses. Compared with unirradiated sample, carbonyl groups, which generated from the molecular chains of agarose hydrogels, were observed at 25 kGy and increased gradually with dose. The main gas products evolved from irradiated agarose hydrogels were H₂, CO₂, CO and CH₄. Based on the analysis of radiolytic products, the radiolysis mechanism of agarose hydrogels under γ-radiation was proposed.

520

The gamma-ray linear and the mass attenuation coefficients of Pb, Al, Cu, and plexiglass materials were calculated from both experimental and theoretical (simulation) methods. For the experimental results, a spectrometer, which was consisted of a NaI(Tl) inorganic scintillation detector, was used. The theoretical attenuation values were calculated by means of the FLUKA Monte Carlo (MC) and XCOM programs. Obtained attenuation coefficients from the experiment and the theoretical methods were compared with each other and literature values.

640

Trapezoidal pulse shaping algorithm is widely applied to improve signal-to-noise ratio (SNR), throughput and energy resolution with the properties of noise suppression, pile-up pulse separation and ballistic deficit correction. The algorithm can be acquired by z transform method which is easier for derivation. However, the baseline drift of trapezoidal pulse appears because the noise superimposes on the input signal. In this paper, two new methods based on convergence analysis and noise suppression are proposed to remove the baseline drift resulting from trapezoidal pulse shaping. Simulations and experimental tests are carried out to verify the methods. The results demonstrate that the proposed methods can remove baseline drift in trapezoidal pulse shaping.

495

This paper tries to address the problem of binary CT image reconstruction in non-destructive detection with an algorithm based on compressed sensing (CS) and Otsu’s method, which could reconstruct binary CT image of test object from incomplete detection data. According to binary CT image characteristics, we employ Split-bregman method based on L_1/2 regularization to solve piecewise constant region reconstruction. To improve the reconstructed image quality from incomplete detection data, we utilize a priori knowledge and Otsu’s method as the optimization constraint. In our study, we make numerical simulation to investigate our proposed method, and compare reconstructed results from different reconstruction methods. Finally, the experimental results demonstrate that the proposed method could effectively reduce noise and suppress artifacts, and reconstruct high-quality binary image from incomplete detection data.

369

Experimental evidence is presented showing obvious azimuthal dependence of single event upsets (SEU) and multiple-bit upset (MBU) patterns in radiation hardened by design (RHBD) and MBU-sensitive static random access memories (SRAMs), due to the anisotropic device layouts. Depending on the test devices, a discrepancy from 24.5% to 50% in the SEU cross sections of dual interlock cell (DICE) SRAMs is shown between two perpendicular ion azimuths under the same tilt angle. Significant angular dependence of the SEU data in this kind of design is also observed, which does not fit the inverse-cosine law in the effective LET method. Ion trajectory-oriented MBU patterns are identified, which is also affected by the topological distribution of sensitive volumes. Due to that the sensitive volumes are periodically isolated by the BL/BLB contacts along the Y-axis direction, double-bit upsets along the X-axis become the predominant configuration under normal incidence. Predominant triple-bit upset and quadruple-bit upset patterns are the same under different ion azimuths (L-shaped and square-shaped configurations, respectively). Those results suggest that traditional RPP/IRPP model should be promoted to consider the azimuthal and angular dependence of single event effects in certain designs. During earth-based evaluation of SEE sensitivity, worst case beam direction, i.e., the worst case response, should be revealed to avoid underestimation of the on-orbit error rate.

317

In advanced technologies, single event upset reversal (SEUR) due to charge sharing can make the upset state of SRAM cells recover to their initial state, which can reduce the soft error for SRAMs in radiation environments. By using the full 3D TCAD simulations, this paper presents a new kind of SEUR triggered by the charge collection of the Off-PMOS and the delayed charge collection of the On-NMOS in commercial 40-nm 6 T SRAM cells. The simulation results show that the proposed SEUR can not occur at normal incidence, but can present easily at angular incidence. It is also found that the width of SET induced by this SEUR remains the same after linear energy transfer (LET) increases to a certain value. In addition, through analyzing the effect of the spacing, the adjacent transistors, the drain area, and some other dependent parameters on this new kind of SEUR, some methods are proposed to strengthen the recovery ability of SRAM cells.

418

A simulation approach is developed to obtain the linear energy transfer (LET) spectrum of all secondary ions and predict single event upset (SEU) occurrence induced by neutron in memory devices. Neutron reaction channels, secondary ion species and energy ranges, and LET calculation method are introduced respectively. Experimental results of neutron induced SEU effects on static random access memory (SRAM) and programmable read only memory (EEPROM) are presented to confirm the validity of the simulation results.

511

The key to large-scale parallel solutions of deterministic particle transport problem is single-node computation performance. Hence, single-node computation is often parallelized on multi-core or many-core computer architectures. However, the number of on-chip cores grows quickly with the scale-down of feature size in semiconductor technology. In this paper, we present a scalability investigation of one energy group time-independent deterministic discrete ordinates neutron transport in 3D Cartesian geometry (Sweep3D) on Intel’s Many Integrated Core (MIC) architecture, which can provide up to 62 cores with four hardware threads per core now and will own up to 72 in the future. The parallel programming model, OpenMP, and vector intrinsic functions are used to exploit thread parallelism and vector parallelism for the discrete ordinates method, respectively. The results on a 57-core MIC coprocessor show that the implementation of Sweep3D on MIC has good scalability in performance. In addition, the application of the Roofline model to assess the implementation and performance comparison between MIC and Tesla K20C Graphics Processing Unit (GPU) are also reported.

576

The nuclear level density and entropy were calculated for ¹⁰⁵Cd, ¹⁰⁶Cd, ¹¹¹Cd and ¹¹²Cd based on the Back Shifted Fermi Gas (BSFG) model and the Constant Temperature (CT) model. Then, the entropies were extracted in the microcanonical ensemble according to recent experimental data on nuclear level density measured by the Oslo group for these nuclei and are compared with their corresponding macroscopic calculations. Entropies of the neutron hole were estimated from the entropy difference between the odd-mass and even-even nuclei. The results reveal that the CT model describes better the extracted microcanonical results.

489

DNA origami technique, a breakthrough in DNA nanotechnology, has been widely used to prepare complex DNA nanostructures with nanoscale addressability. However, the purity and yield are generally the bottleneck to application of DNA nanostructures, and current methods for purifying DNA origami nanostructures in large quantities are time-consuming and laborious. This study aims to develop a scalable, cost-effective and contamination-free method of purifying DNA origami nanostructures. We employ an effective and convenient purification approach to purify planar rectangle DNA origami structures through rate-zonal centrifugation. By subjecting DNA origami samples to high centrifugal force in a density gradient media of glycerol, well-folded nanostructures and by-products are separated successfully, which are confirmed by agarose gel electrophoresis and atomic force microscopy (AFM). This method will aid the production of pure rectangle DNA origami nanostructures in large quantity.

438

As a potential candidate for generation IV reactors, lead-alloy cooled reactor has attracted much attentions in recent years. The China LEAd-based research Reactor (CLEAR) is proposed as the primary choice for the accelerator driven subcritical system project launched by Chinese Academy of Sciences. Lead-bismuth eutectic (LBE) is selected as the coolant of CLEAR owing to its efficient heat conductivity properties and high production rate of neutrons. In order to compensate the buoyancy due to the high density of lead-alloy, fixation methods of fuel assembly (FA) have become a research hotspot worldwide. In this paper, we report an integrated system of ballast and fuel element for CLEAR FA. It guarantees the correct positioning of each FA in normal and refueling operations. Force calculation and temperature analysis prove that the FA will be stable and safe under CLEAR operation conditions.

386

Probabilistic safety assessment (PSA) is important in nuclear safety review and analysis. Because the design and physics of the fluoride salt-cooled high temperature reactor (FHR) differ greatly from the pressurized water reactor (PWR), the methods and steps of PSA in FHR should be studied. The high-temperature gas-cooled reactor (HTR-PM) and sodium-cooled fast reactors have built the PSA framework, and the framework to finish the PSA analysis. The FHR is compared with the PWR, HTR-PM and sodium-cooled fast reactors from the physics, design and safety. The PSA framework of FHR is discussed. In the FHR, the fuel and coolant combination provides large thermal margins to fuel damage (hundreds of degrees centigrade). The tristructural-isotropic (TRISO) as the fuel is independent in FHR core and its failure is limited for the core. The core damage in Level 1 PSA is of lower frequency. Levels 1 and 2 PSA are combined in the FHR PSA analysis. The initiating events analysis is the beginning, and the source term analysis and the release types are the target. Finally, Level 3 PSA is done.

399

In large-scale, loosely coupled systems, Monte Carlo criticality calculation always suffers from slow fission source convergence resulting from the high dominance ratio. The fission matrix acceleration method has shown its potential to accelerate the convergence of the fission source in many numerical simulations. In practice, however, instability of this method may be caused by imbalanced precisions of elements of the fission matrix. Hence, an improved method, in which the space mesh used to compute the fission matrix is defined adaptively based on the fission bank in each cycle, is introduced. The proposed method ensures balanced precisions of elements of the fission matrix, so is more stable than the existing fission matrix method.

462