Low energy accelerator driven neutron sources are promising candidates to obtain a neutron yield as high as 1014 n/s, which is required for a variety of applications, such as boron neutron capture ...therapy, neutron imaging, and neutron scattering. The methods to generate neutrons can be divided into two categories: hadron-based and photon-based methods. In order to better understand which kind of source would be the better choice for delivering a brilliant neutron beam robustly, in this paper, the underlying principles of neutron production, as well as the simulation results of neutron yield, target heat dissipation, thermal stress, and reaction byproducts concentration of these two types of neutron sources, will be elaborated on. A preliminary photoneutron target station design based on a 50 MeV/50 kW electron linear accelerator, including the optimized neutron yield, thermal hydraulic analysis, and shielding calculation, is presented as well to demonstrate the method to deliver brilliant thermal neutron beam of 1.03 × 1010 cm−2 s−1 sr−1.
Urbanization often exerts multiple effects on aquatic and terrestrial organisms, including changes in biodiversity, species composition and ecosystem functions. However, the impacts of urbanization ...on river phytoplankton in subtropical urbanizing watersheds remain largely unknown. Here, we explored the effects of urbanization on phytoplankton community structure (i.e., biomass, community composition and diversity) and function (i.e., resource use efficiency) in a subtropical river at watershed scale in southeast China over 6 years. A total of 318 phytoplankton species belonging into 120 genera and 7 phyla were identified from 108 samples. Bacillariophyta biomass showed an increasing trend with increasing urbanization level. The phytoplankton community shifted from Chlorophyta dominance in rural upstream waters to Bacillariophyta dominance in urbanized downstream waters. Furthermore, phytoplankton diversity and resource use efficiency (RUE = phytoplankton biomass/total phosphorus) were significantly decreased with increasing urbanization level from upstream to downstream. Phytoplankton RUE exhibited a significant positive correlation with species richness, but a negative correlation with phytoplankton evenness. The variation in environmental factors (turbidity, total nitrogen, NH4+-N, total phosphorus, PO43−-P and percentage urbanized area) was significantly correlated with phytoplankton diversity and RUE. Overall, our results revealed the influence of urbanization on phytoplankton community structure and ecosystem function was due to its altering the environmental conditions. Therefore, human-driven urbanization may play crucial roles in shaping the structure and function of phytoplankton communities in subtropical rivers, and the mechanism of this process can provide important information for freshwater sustainable uses, watershed management and conservation.
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Both X-ray imaging and neutron imaging are essential methods in non-destructive testing. In this work, a bimodal imaging method combining neutron and X-ray imaging is introduced. The experiment is ...based on a small electron accelerator-based photoneutron source that can simultaneously generate the following two kinds of radiations: X-ray and neutron. This identification method utilizes the attenuation difference of the two rays’ incidence on the same material to determine the material’s properties based on dual-imaging fusion. It can enhance the identification of the materials from single ray imaging and has the potential for widespread use in on-site, non-destructive testing where metallic materials and non-metallic materials are mixed.
A new design of the boron-lined gaseous neutron detector composed of a boron-lined honeycomb neutron converter and an electron multiplier is proposed in this paper. The motivation for this research ...was to decrease the manufacturing difficulty and improve the robustness of the boron-lined gaseous neutron detector. The numerous anode wires in the traditional designs were removed, and the gas electron multiplier (GEM) was used as the electron multiplier. To drive the ionized electrons produced inside the honeycomb structure out to the incident surface of the GEM, a drift electric field was applied inside the holes of the honeycomb structure. The design principles of this detector were discussed. Geant4, Maxwell11, and Garfield9 were used to estimate the neutron absorption efficiency and the electron migration process. A prototype detector was constructed and experimentally evaluated. Both the simulation and experimental results indicate that this detector has the potential to be used in the applications of small angle neutron scattering for scientific research, and to replace the currently used 3 He detectors, which have the trouble of very limited supply of 3 He gas.
To reduce the manufacturing difficulty and improve the robustness of traditional boron-lined detectors that may replace the 3 He counter, the honeycomb neutron converter-based gaseous neutron ...detector has been proposed. A drift electric field is applied to drive electrons ionized by α or 7 Li after the 10 B(n, α) 7 Li reaction from their origination positions to the incident surface of the gas electron multiplier (GEM), which multiplies electrons and forms the neutron signal. As the working gas affects the energy deposition of α or 7 Li, the transverse diffusion of electrons in the migration process, as well as the multiplication of electrons in the GEM detector, the working gas selection of the honeycomb converter-based detector would be very important. Fourteen different working gases are investigated in detail through simulation research. Four working gases, Ar:iC 4 H 10 :CF 4 = 90:7:3, Ar:CO 2 = 95:5, Ar:CH 4 = 90:10, and Ar:DME = 95:5, are experimentally tested. Both the simulation and experimental results demonstrate that working gases of Ar:iC 4 H 10 :CF 4 = 90:7:3, Ar:CO 2 = 95:5, and Ar:DME = 95:5 show good performances benefitting from both the large stopping powers of α or 7 Li and the small transverse diffusion coefficients of electrons. The simulation results indicate that the detection efficiency with one of the three gases is 1.33 to 1.48 times the Ar:CH 4 = 90:10, while the experimental results demonstrate that there is 1.34-1.49 times of the detection efficiency. The research in this paper helps improve the performance of the honeycomb converter-based neutron detector.
To explore the detection of impact sound insulation performance of nano-inorganic composite floor slabs for green buildings, for 4 types of floor slab practices in a certain area, we carry out the ...detection of the sound insulation performance of the floor impact sound and analyze and summarize the test results. Finally, several common technical measures to effectively improve the sound insulation performance of floor impact sound are summarized. Experimental results show that with floor slabs using nano-inorganic composite material FBP, the impact sound insulation performance of the floor slab can be greatly improved. FRP materials have the advantages of high strength, lightweight, and good corrosion resistance. They are more and more widely used in construction engineering. At this stage, for environmental friendly green building materials and nano-inorganic composite materials with certain effects, their main practice and application play an important role. It is proved that adding FBP material can greatly improve the impact sound insulation performance of floor slabs.
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•12-tungstophosphoric acid (TPA) immobilized on Sn-based MOFs (Sn(II)-BDC) was successfully fabricated with water as a solvent.•The TPA/Sn(II)-BDC catalyst exhibits excellent ...catalytic activity and recyclability.•The highest conversion of oleic acid (91.7%) was achieved over TPA/Sn(II)-BDC.•Reaction kinetics were evaluated for oleic acid esterification.
Facilitating energy resource deficiency and environmental contamination, this work focuses on sustainable biodiesel production through the esterification reactions of oleic acid (OA) with methanol. To address the reaction, a novel heterogeneous acid catalyst, 12-tungstophosphoric acid (TPA) immobilized on Sn-based MOFs (Sn(II)-BDC) was synthesized via a simple, green solvent, and easy-to-implement synthesis strategy for the first time, and applied effectively for esterification process of OA to produce biodiesel. The structure and composition of as-obtained catalyst have been verified using XRD, FTIR, N2 physisorption, SEM, EDX, TG, Py-FTIR, TPD-NH3, and XPS techniques. The obtained TPA/Sn(II)-BDC catalyst was found to be the best with 60 wt% of TPA loading, which resulted in an OA conversion of 91.7 % at optimized conditions of 0.15 g catalyst loading and methanol to OA molar ratio of 20:1 at temperature of 120 °C in 4 h, and the excellent performance arises from available pores structure, large amounts of acidic sites, good stability and the synergistic catalytic effect of TPA and Sn(II)-BDC. Furthermore, the composite catalyst reusability has been studied for five cycles, and it exhibits an acceptable conversion. This research provides a green and large-scale synthesis route for the sustainable production of biofuels by constructing heteropolyacids/Sn-based MOFs synergistic catalysts.
Contraband-detection systems can use X-rays and photoneutrons delivered from the same 7-MeV electron linear accelerator (e-LINAC) to stimulate and extract information from inspected materials. The ...X-ray attenuation information is used to measure the mass thickness, which is combined with the photoneutron attenuation information to categorize inspected materials as common organic materials, metals, and heavy metals. Once a heavy metal is found, the beta-delayed neutrons stimulated by the (γ,fission) reaction are measured by a polyethylene-moderated 3 He counter to clarify if the material is fissile. The presence of neutron events 2000 μs after the X-ray pulse confirms the existence of the fissile material. The isotopes in the material are then identified using the time-of-flight method to analyze the resonant attenuation of the fissile material to the 10 -1 -10 2 eV photoneutrons emitted from and thermalized by the D 2 O photonto-neutron convertor, which converts X-rays to photoneutrons. Eight high-Z simulants are tested to confirm the feasibility of identifying the isotopes from the photoneutron resonance. The underlying principles and experimental results are discussed.
Yield calculation for delayed gamma-ray neutron activation analysis Cui, Tongyuan; Yang, Yigang
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
September 2023, 2023-09-00, Letnik:
1054
Journal Article
Recenzirano
Predicting the analysis sensitivities of interested elements is one of the major concerns in various applications of neutron activation analysis (NAA). As the specific gamma-ray yield after the ...neutron irradiation could be affected by the irradiating neutrons’ spectrum, which can hardly be constant for NAA applications of different interested elements (and matrix elements) that need their own customized optimal neutron moderators, a calculator for predicting the analysis sensitivities of NAA should be able to consider all the contributions of neutrons with different energies. In this study, a MATLAB-based code, named as CYANUS (the Calculator for Yield Analysis of NeUtron Activation) is developed to quantitatively evaluate the specific yields of delayed gamma-rays released from the neutron irradiated objects. The comparison between the results calculated by CYANUS and those from other currently available online programs demonstrates that this work shows the smallest relative error with respect to the experimentally measured results, indicating that CYANUS is promising to provide an accurate evaluation of the specific gamma-ray yields when the object is irradiated by customized neutron spectrum in the NAA applications.
Oligosaccharides, as a wide type of polysaccharide, have a broad antimicrobial spectrum and promote development as plant growth stimulants. To investigate the regulation effects of different ...oligosaccharides on the dynamic changes of chlorophyll content, leaf fluorescence, root activity and morphology, and chloroplast ultrastructure, as well as the yields and yield components of strawberry and cucumber, typical greenhouse experiments were conducted over two years (2021–2022). The experimental plants were foliar sprayed with tap water (CK), chitosan oligosaccharide (CSOS), and mixed oligosaccharides (MixOS) five times before flowering. The conventional management (CM) was conducted as a conventional control. The findings of the present study suggest that the application of MixOS has the greatest regulation effects on delayed leaf senescence, well-developed roots, and higher fruit productions of strawberry and cucumber. Exogenous MixOS resulted in significant increases in SPAD values, maximum photochemical efficiency (Fv/Fm), and photochemical quenching coefficiency (qP); they were increased by 1.94–28.96%, 5.41–33.89%, and 9.93–62.07%, compared to the CSOS, CM, and CK treatments, respectively. The orderly and steady structure of thylakoids in the chloroplast, and the randomly distributed starch grains, could be clearly observed in the MixOS treatment, while the non-photochemical quenching (NPQ) was correspondingly reduced by 19.04–45.92%. Meanwhile, the remarkable promotion of root activity and root surface morphology indicators (i.e., root length, surface area, average diameter, and volume) could be observed when exposed to the MixOS treatments, and the total yields of strawberry and cucumber were all increased by 12.40–25.57%. These findings suggest that the mixed oligosaccharides mainly promote the coordinated growth of root and shoot, which leads to the improved yields of strawberry and cucumber.
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