Vol.30,

Analyses of chemical bonding and geometric structures in species with chalcogen elements EThF₂ (E = O, S, Se, Te) are performed by the density functional theory. Kohn-Sham molecular orbitals and Th-E bond lengths of these species both indicate multiple bond character for the terminal chalcogen complexes. This is also confirmed by natural bond orbital (NBO) analyses using the one-electron density matrix generated by relativistic density functional calculations. Theoretical analyses indicate that electron donation from E to Th increases down the chalcogen group (O < S < Se < Te). These molecules can serve as examples of multiple bonding between actinide elements and selenium or tellurium.

352

Cerenkov luminescence imaging (CLI) has been widely investigated for biological imaging. However, the luminescence generated from Cerenkov Effect is relatively weak and has poor penetration ability in biological tissues. These limitations consequently hindered the clinical translation of CLI. In this study, we proposed an in-vitro experimental study for the demonstration of quantum dots (QDs) configurations affected by the improvement of the signal intensity of CLI. Results revealed that the optimal concentrations were 0.1 mg/mL and 0.25 mg/mL for the studied CdSe/ZnS QDs with fluorescence emission peaks of 580 nm and 660 nm, respectively. The detected optical signal intensity with long-wavelength emission QDs were stronger than those with short-wavelength emission QDs. This study illustrates an experiment to study the effects of concentrations and fluorescence emission peaks of QDs on an enhanced optical signal for the external detection of CLI.

512

The impregnation behavior of molten 2LiF-BeF₂ (FLiBe) salt into a graphite matrix of fuel elements for a solid fuel thorium molten salt reactor (TMSR-SF) at pressures varying from 0.4 MPa to 1.0 MPa was studied by mercury intrusion, molten salt impregnation, X-Ray diffraction, and scanning electron microscopy techniques. It was found that the entrance pore diameter of the graphite matrix is less than 1.0 µm and the contact angle is about 135°. The threshold impregnation pressure was found to be around 0.6 MPa experimentally, consistent with the predicted value of 0.57 MPa by the Washburn equation. With the increase of pressure from 0.6 MPa to 1.0 MPa, the average weight gain of the matrix increased from 3.05% to 10.48%, corresponding to an impregnation volume increase from 2.74% to 9.40%. The diffraction patterns of FLiBe are found in matrices with high impregnation pressures (0.8 MPa and 1.0 MPa). The FLiBe with sizes varying from tens of nanometers to a micrometer mainly occupies the open pores in the graphite matrix. The graphite matrix could inhibit the impregnation of the molten salt in the TMSR-SF with a maximum operation pressure of less than 0.5 MPa.

483

The present study explored the 18-kDa translocator protein radioligand ¹⁸F-PBR06 as a PET imaging biomarker for diagnosis of inflammation and compared it with ¹⁸F-FDG for differentiation of inflammation and lung tumors in animals. ¹⁸F-PBR06 was synthesized with an average decay corrected radiochemical yield of 30%–40% (end of synthesis, EOS), and the radiochemical purity was greater than 99%. The inflammation-to-blood ratio of ¹⁸F-PBR06 (3.53 ± 0.26) was higher than the tumor-to-blood ratio (1.77 ± 0.35) (P < 0.001). The inflammation-to-muscle ratio of ¹⁸F-PBR06 (2.33 ± 0.64) was also higher than the tumor-to-muscle ratio (1.45 ± 0.14) (P = 0.036). Micro-PET/CT images showed high uptake of ¹⁸F-FDG in both inflamed muscles and lung tumor tissues. However, ¹⁸F-PBR06 uptake in inflamed muscles remained higher than that in the lung tumor tissues, following 90 min of dynamic Micro-PET/CT imaging. Further, macrophages in the inflammatory regions showed a higher fluorescence signal than in lung tumor tissues. Results of the study confirmed that ¹⁸F-PBR06 PET/CT imaging allowed for diagnosis of inflammation. Moreover, ¹⁸F-PBR06 uptake in the inflammatory regions was significantly higher than in lung tumor tissues, suggesting that ¹⁸F-PBR06 PET/CT imaging has potential to differentiate between peripheral lung cancer and inflammation nodules.

369

Free electron lasers (FELs) provide high-power and ultrashort pulses with extreme brightness. In order to improve a facility’s capabilities and explore the possibility of performing high resolution time-resolved experiments, a beam arrival time resolution under 100 fs is required. In this article, a novel beam arrival time monitor (BAM) equipped with two cavities has been designed and a beam flight time measurement scheme based on the BAM prototype has been proposed to estimate phase jitter in the signal measurement system. The two BAM cavities work at different frequencies and the frequency difference is designed to be 35 MHz. Therefore, a self-mixing intermediate frequency (IF) signal can be generated using the two cavities. The measured beam flight time shows a temporal deviation of 37 fs (rms).

339

In the past few decades, various surface analysis techniques find wide applications in studies of interfacial phenomena ranging from fundamental surface science, catalysis, environmental science and energy materials. With the help of bright synchrotron sources, many of these techniques have been further advanced into novel in situ/operando tools at synchrotron user facilities, providing molecular level understanding of chemical/electrochemical processes in situ at gas-solid and liquid-solid interfaces. Designing a proper endstation for a dedicated beamline is one of the challenges in utilizing these techniques efficiently for a variety of user’s requests. Many factors, including pressure differential, geometry and energy of the photon source, sample and analyzer, need to be optimized for the system of interest. In this paper, we discuss the design and performance of a new endstation at beamline 02B at the Shanghai Synchrotron Radiation Facility (SSRF) for ambient pressure X-ray photoelectron spectroscopy (APXPS) studies. This system, equipped with the newly developed high-transmission HiPP-3 analyzer, is demonstrated to be capable of efficiently collecting photoelectrons up to 1500 eV from ultrahigh vacuum (UHV) to ambient pressure of 20 mbar. The spectro-microscopy mode of HiPP-3 analyzer also enables detection of photoelectron spatial distribution with resolution of 2.8±0.3 µm in one dimension. In addition, the designing strategies of systems that allow investigations in phenomena at gas-solid interface and liquid-solid interface will be highlighted through our discussion.

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A bunch arrival-time monitor (BAM) system, based on electro-optical intensity modulation scheme, is under study at Shanghai soft X-ray Free Electron Laser (SXFEL). The aim of the study is to achieve high-precision time measurement for minimizing bunch fluctuations. A readout electronics is developed to fulfill the requirements of the BAM system. The readout electronics is mainly composed of a signal conditioning circuit, Field-Programmable Gate Array (FPGA), Mezzanine Card (FMC150), and powerful FPGA carrier board. The signal conditioning circuit converts the laser pulses into electrical pulse signals using a photodiode. Thereafter, it performs splitting and low noise amplification to achieve the best voltage sampling performance of the dual channel Analog-to-Digital Converter (ADC) in FMC150. The FMC150 ADC daughter card includes a 14-bit 250 Msps dual channel high-speed ADC, a clock configuration, and a management module. The powerful FPGA carrier board is a commercial high-performance Xilinx Kintex-7 FPGA evaluation board. To achieve clock and data alignment for ADC data capture at a high sampling rate, we used ISERDES, IDELAY, and dedicated carry-in resources in the Kintex-7 FPGA. This paper presents a detailed development of the readout electronics in the BAM system and its implementation performance.

352

A novel simple, sensitive, rapid, direct, and spectrophotometric-based procedure was investigated to determine Th(IV) at trace amounts. The new method is based on Th(IV) chelation with 3,6–dichloro-2,5-dihydroxy–l,4-benzoquinone (DDBQ). The reagent reacts with Th(IV) in 0.1M HCl to form an orange 1:2 complex. The stability constant value is 6.62×10⁴ for the Th(IV)-complex. The Th(IV)-DDBQ obtained shows one peak with a maximum at about 346 nm. The chelate forms immediately and the absorbance remains stable for over 24 h. Beer’s law was obeyed in the concentration range 0-10 µg·mL⁻¹. The molar absorptivity and Sandell’s sensitivity were 4.4×10⁴ L·mol⁻¹·cm⁻¹ and 0.0053 μg.cm⁻², respectively. Different analytical parameters were tested in detail. Interfering ion (cations and anions) effects were tested. Methods for Th(IV) determination by second and third-derivative spectrophotometry were also introduced at about 344 and 341 nm, respectively. These two derivative orders offer the feature of sensitivity without the necessity for solvent extraction, heating, or pre-concentration steps. Finally, the methods were successfully utilized for Th(IV) determination in monazite, environmental water, and wastewater samples.

424

This study investigates the risks of non-conservative piping design according to ASME B31.1 for high-temperature piping subjected to long-term operation at high temperature in a creep regime based on a sensitivity analysis of the hold time. Design evaluations of high-temperature piping were conducted over a range of hold times in the creep regime according to ASME B31.1, which implicitly considers the creep effects, and the French high-temperature design code of the RCC-MRx, which explicitly considers the creep effects. Conservatisms were quantified among the codes in terms of the hold times. In the case of B31.1, the design evaluation results do not change depending on the hold time at high temperature, whereas in the case of RCC-MRx, they do. It was shown that the design limits of RCC-MRx were exceeded when the hold time exceeded certain values, whereas those of B31.1 were satisfied regardless of the hold times. Thus, the design evaluations according to B31.1 did not consistently yield conservative results and might lead to non-conservative results in the case of long-term operations in the creep range.

657

The thorium molten salt reactor–liquid fuel (TMSR-LF1) has inherent safety features. The accident occurrence possibility and their consequences are much lower for the TMSR-LF1 than that of traditional reactors. Based on accident analysis, the maximum credible accident and the radioactive source terms of the TMSR-LF1 were first estimated. Then, the total effective dose of the maximum credible accident was calculated. Based on calculations, the cover gas flow rate can significantly affect the radiation consequences of the maximum credible accident when it changes from 0 to 10 L/min. If no cover gas is flowing, a site area emergency would be required within the range of 50–73 m from the reactor. In the case of cover gas flow, only an abnormal notification and an alert two emergency class would be required within the range of 50 m.

483

In this study, a displacement–reactivity feedback model, which can directly represent the inherent "thermal expansion extinction effect" of Fast Burst Reactors (FBRs), was developed with the aid of the static neutron transport component of the FBR–MPC code. Dynamic behaviors of bursts in the Godiva I reactor were simulated by coupling the simplified multiphysics models consisting of the point kinetic equations for neutronics, adiabatic equation for temperature, and thermoelastic equations for displacement/stress with the developed model. The results were compared with the corresponding experimental data and those obtained using the traditional fission yield (temperature rise)–reactivity feedback models. It was found that the developed model can provide good results for the bursts with no or a small inertia effect. For the bursts with a prominent inertia effect, the smaller burst width and asymmetric distribution of the fission rate curve, noticed in the experiments but not evident using the traditional models, can be reproduced. In addition, the realistic oscillations in reactivity and fission rate caused by the core vibration, as well as the deeper sub–prompt criticality in the plateau following the burst, can be observed. Therefore, the developed displacement–reactivity feedback model can be expected to be an effective tool for calculating the dynamic behaviors of bursts.

348

The calculation time in the Monte Carlo simulations, consistently represents an essential issue. It is often very long, and its decrease constitutes a challenge for the simulator. Generally, an MC simulation is qualified as quality or not according to two main criteria: The calculation time and the accuracy of the results. However, in most cases, the optimization of one criterion affects negatively the other. Therefore, a compromise between both of them is always required in this kind of simulation. The present work aims at studying the impact of the production threshold (or cut) of the GEANT4 toolkit on the calculation of the power deposition in the MEGAPIE spallation target. The production threshold of secondaries is a GEANT4 intrinsic parameter. It indicates the limit of energy we can reach in the production of secondary particles. This study has allowed us to make the following conclusions. First, the influence of the cut on the calculation of the deposited power depends on the volume size, its arrangement, and the importance of the electromagnetic processes occurring within. Second, the accuracy of the calculations can be acceptable only below a given value of the cut energy. Third, this accuracy remains almost unchangeable from a certain value of the cut. The study has also made it possible to explore the prevalence of certain interactions in the zone of spallation in the MEGAPIE target.

428

In this study, a scintillation detector was developed to measure the space proton effective dose for astronauts based on the proton effective dose conversion coefficients provided by ICRP (International Commission on Radiological Protection) Report No. 116. In the MCNPX (Monte Carlo N-Particle Transport Code X, Version 2.6.0) simulation process, by modulating the depth and solid angle of truncated conical holes in an iron shell from lower-energy protons to higher-energy protons, the energy deposited in the scintillator by isotropic protons was nearly proportional to the corresponding effective dose, with a maximum relative deviation of 13.28% at thirteen energy points in the energy range of 10–400 MeV. Therefore, the detector can monitor proton effective dose indirectly in real time by measuring the deposited energy. We calibrated the photoelectric conversion efficiency of the detector at the cobalt source, tested the response of the detector in the energy range of 30–100 MeV in unidirectional proton field, and validated the simulation with the experimental results.

429

Single event effects of 1-T structure programmable read-only memory (PROM) devices fabricated with a 130-nm complementary metal oxide semiconductor (CMOS)-based thin/thick gate oxide anti-fuse process were investigated using heavy ions and a picosecond pulsed laser. The cross sections of a single event upset (SEU) for radiation-hardened PROMs were measured using a linear energy transfer (LET) ranging from 9.2 to 95.6 MeV·cm²·mg^-1. The result indicated that the LET threshold for a dynamic bit upset was ~9 MeV·cm²·mg^-1, which was lower than the threshold of ~20 MeV·cm²·mg^-1 for an address counter upset owing to the additional triple-modular-redundancy structure present in the latch. In addition, a slight hard error was observed in the anti-fuse structure when employing ²⁰⁹Bi ions with extremely high LET values (~91.6 MeV·cm²·mg^-1) and large ion fluence (~1 × 10⁸ ions·cm^-2). To identify the detailed sensitive position of an SEU in PROMs, a pulsed laser with a 5-μm beam spot was used to scan the entire surface of the device. This revealed that the upset occurred in the peripheral circuits of the internal power source and I/O pairs rather than in the internal latches and buffers. This was subsequently confirmed by a ¹⁸¹Ta experiment. Based on the experimental data and a rectangular parallelepiped (RPP) model of the sensitive volume, the space error rates for the used PROMs were calculated using the CRÈME-96 prediction tool. The results showed that this type of PROM was suitable for specific space applications, even in the geosynchronous orbit.

396

An adaptable and compact fast pulse sampling module was developed for the neutron-gamma discrimination. The developed module is well suited for low cost and low power consumption applications. It is based on the Domino Ring Sampler 4 (DRS4) chip, which offers fast sampling speeds up to 5.12 giga samples per second (GSPS) to digitize pulses from front end detectors. The high resolution GSPS data is useful for obtaining precise real-time neutron-gamma discrimination results directly in this module. In this study, we have implemented real-time data analysis in a field programmable gate array. Real-time data analysis involves two aspects: digital waveform integral and digital pulse shape discrimination (PSD). It can significantly reduce the system dead time and data rate processed offline. Plastic scintillators (EJ-299-33), which have proven capable of PSD, were adopted as neutron detectors in the experiments. A photomultiplier tube (PMT) (model #XP2020) was coupled to one end of a detector to collect the output light from it. The pulses output from the anode of the PMT were directly passed onto the fast sampling module. The fast pulse sampling module was operated at 1 GSPS and 2 GSPS in these experiments, and the AmBe-241 source was used to examine the neutron-gamma discrimination quality. The PSD results with different sampling rates and energy thresholds were evaluated. The figure of merit (FOM) was used to describe the neutron-gamma discrimination quality. The best FOM value of 0.91 was obtained at 2 GSPS and 1 GSPS sampling rates with an energy threshold of 1.5 MeV_ee (electron equivalent).

489

A compact D-D neutron generator, with a peak neutron yield of D-D reactions up to 2.48 × 10⁸ n/s is being developed at Lanzhou University in China for application in real-time neutron activation analysis. During tests, the problem of back-acceleration of secondary electrons liberated from the neutron production target by deuterium ions bombardment was encountered. In this study, an electric field method and a magnetic field method for suppressing secondary electrons are designed and experimentally investigated. The experimental results show that the electric field method is superior to the magnetic field method. Effective suppression of the secondary electrons can be achieved via electrostatic suppression when the bias voltage between the target and the extraction-accelerating electrode is greater than 204 V. Furthermore, the secondary electron emission coefficient for the mixed deuterium ion (D₁⁺_, D₂⁺_, and D₃⁺) impacting on molybdenum is estimated. In the deuterium energy range of 80–120 keV, the estimated secondary electron emission coefficients are approximately 5–5.5 for the mixed deuterium ion glancing incidence of 45° and approximately 3.5–3.9 for the mixed deuterium ion normal-incidence.

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