Search Results (330)

The photolysis kinetics of propaquizafop in water under ultraviolet light was investigated in this study, and the effects of different influencing factors (pH, ${\mathrm{N}\mathrm{O}}_3^{-}$, metal ions) on the photolysis of propaquizafop were clarified. Propaquizafop residues in water were determined by a HPLC-UV detector. The results showed that the pH of the aqueous solution had no significant effect on the photolysis of propaquizafop (p < 0.05). The low ${\mathrm{N}\mathrm{O}}_3^{-}$, concentration (0.5~2 mmol/L) had a weak inhibitory effect on the photolysis of the propaquizafop; when the concentration of ${\mathrm{N}\mathrm{O}}_3^{-}$ was 4 mmol/L, the degradation half-life of the propaquizafop was significantly higher than with other treatments (p < 0.05); Different concentrations of Fe³⁺ had varying degrees of inhibitory effects on the photolysis of propaquizafop. The inhibitory effect was stronger at low concentrations (0.5 mmol/L and 1 mmol/L) and weaker at high concentrations (2 mmol/L and 4 mmol/L). As the concentrations of Cu²⁺, Cd²⁺, Mn²⁺, Zn²⁺, and Ni²⁺ increased, their inhibitory effect on the photolysis of propaquizafop in an aqueous solution became stronger. In addition, LC–QTOF-MS was used to identify the photoproducts of propaquizafop in aqueous solution in this study. Five types of photoproducts were identified, and several propaquizafop degradation pathways and mechanisms were proposed, mainly including rearrangement, cracking reactions, dechlorination reactions, and light-induced redox reactions. The results of this study will help us to better understand the photodegradation law of propaquizafop in aqueous solution and provide data support for its safety evaluation in water. Full article

Tea is one of the most consumed beverages in the world and presents a great aromatic diversity depending on the origin of the production and the transformation process. Volatile organic compounds (VOCs) greatly contribute to the sensory perception of tea and are excellent markers for traceability and quality. In this work, we analyzed the volatile organic compounds (VOCs) emitted by twenty-six perfectly traced samples of tea with two analytical techniques and two data treatment strategies. First, we performed headspace solid-phase microextraction gas chromatography–mass spectrometry (HS-SPME-GC-MS) as the most widely used reference method for sanitary and quality controls of food. Next, we analyzed the samples with selected-ion flow-tube mass spectrometry (SIFT-MS), an emerging method for direct analysis of food products and aroma. We compared the performances of both techniques to trace the origin and the transformation processes. We selected the forty-eight most relevant markers with HS-SPME-GC-MS and evaluated their concentrations with a flame ionization detector (FID) on the same instrument. This set of markers permitted separation of the origins of samples but did not allow the samples to be differentiated based on the color. The same set of markers was measured with SIFT-MS instrument without success for either origin separation or color differentiation. Finally, a post-processing treatment of raw data signals with an untargeted approach was applied to the GC-MS and SIFT-MS dataset. This strategy allowed a good discrimination of origin and color with both instruments. Advantages and drawbacks of volatile profiles with both instruments were discussed for the traceability and quality assessment of food. Full article

This article introduces the design and development of a space environment monitoring unit embedded in the versatile experimental assembly for electronic components outside the China space station’s Wentian laboratory cabin module. A newly designed comprehensive detection system is being used for the first time in this kind of detector. The sensor head of the instrument includes a silicon telescope (composed of two silicon semiconductors) for measuring the LET spectrum and radiation dose rate, a typical chip for monitoring a single-event upset, and a CR-39 plastic nuclear track detector for detecting heavy ion tracks. The two silicon sensors stacked up and down are used for measuring the LET spectrum, which ranges from 0.001 to 100 MeV·cm²/mg. A sensor charge allocation method is adopted to divide the detection range into four cascaded levels, each achieving different detection ranges separately and then concatenated together, while traditional detection methods need multiple sets of probes to achieve the same dynamic range. At the same time, using the two sensors mentioned above, the silicon absorption dose rate under two different shielding thicknesses can be obtained through calculation, ranging from 10⁻⁵ to 10⁻¹ rad (Si)/h. Multiple calibration methods are applied on the ground. The preliminary in-orbit detection results are provided and compared with the simulation results obtained using the existing space environment model, and we analyze and discuss their differences. Full article

A new method for simultaneous determination by liquid chromatography coupled with high resolution mass spectrometry (UHPLC-HRMS/MS) of 14 paralytic shellfish poisoning toxins (PSP), that is, Saxitoxin, Neosaxitoxin, Gonyautoxins and their respective variants, in bivalve molluscs, is herein described. The samples were extracted by acetic acid solution, then analysed by UHPLC coupled with a Q-Exactive Orbitrap Plus high resolution mass spectrometer, by electrospray ionization mode (ESI) with no further clean up step. The analysis was carried out by monitoring both the exact mass of the molecular precursor ion of each compound (in mass scan mode, resolution at 70,000 FWHM) and its respective fragmentation patterns (two product ions) with mass accuracy greater than 5 ppm. The analytical performance of the method was evaluated calculating trueness, as mean recoveries of each biotoxin, between 77.8% and 111.9%, a within-laboratory reproducibility (RSD_R) between 3.6% and 12.2%, the specificity, the linearity of detector response, and the ruggedness for slight changes The results of the validation study demonstrate this method fits for the purposes of the official control of PSP toxins in molluscs. The results of two years of monitoring in local mussel farms are also reported, showing that no significant concerns for food safety in the monitored productions. Full article

This study presents the results of investigating the interaction between the CeF₃–EuF₃ system and the NaCl–KCl salt melt using spectroscopic methods. It was found that CeF₃ ions undergo no significant changes upon dissolution in the NaCl–KCl melt. In contrast, the dissolution of EuF₃, both individually and within the CeF₃–EuF₃ system, is accompanied by redox reactions leading to the formation of Eu²⁺. The diffuse reflectance spectra of both the bottom (insoluble sediment) and upper parts of the solidified salt melt in the UV range indirectly indicate photoluminescence excitation from Ce³⁺ and Eu²⁺ ions. In addition, absorption bands in the near-IR region (1900–2300 cm⁻¹) confirm the retention of some Eu³⁺ ions in the salt melt. The study explored the effects of various factors—including sample composition, excitation wavelength, prior and subsequent heat treatment, and medium composition—on the excitation and emission spectra of the samples. Intense 5d-4f luminescence of Ce³⁺ and Eu²⁺ ions (at 330 and 430 nm, respectively) was observed predominantly in the upper part of the salt melts, along with much weaker 4f-4f luminescence from Eu³⁺ ions. Certain parameters were optimized to reduce the luminescence contribution from Ce³⁺ and especially Eu³⁺ ions while enhancing the luminescence of Eu²⁺ ions. Solidified salt solution-melts of the NaCl–KCl–CeF₃–EuF₃ system show promise as materials for developing solar ultraviolet radiation detectors. Full article

Timing and/or position-sensitive MCP detectors, which detect secondary electrons (SEs) emitted from a conversion foil during ion passage, are widely utilized in nuclear physics and nuclear astrophysics experiments. This review covers high-performance timing and/or position-sensitive MCP detectors that use SE emission for mass measurements of exotic nuclei at nuclear physics facilities, along with their applications in new measurement schemes. The design, principles, performance, and applications of these detectors with different arrangements of electromagnetic fields are summarized. To achieve high precision and accuracy in mass measurements of exotic nuclei using time-of-flight (TOF) and/or position (imaging) measurement methods, such as high-resolution beam-line magnetic-rigidity time-of-flight (B$\rho$-TOF) and in-ring isochronous mass spectrometry (IMS), foil-MCP detectors with high position and timing resolution have been introduced and simulated. Beyond TOF mass measurements, these new detector systems are also described for use in heavy ion beam trajectory monitoring and momentum measurements for both beam-line and in-ring applications. Additionally, the use of position-sensitive timing foil-MCP detectors for Penning trap mass spectrometers and multi-reflection time-of-flight (MR-TOF) mass spectrometers is proposed and discussed to improve efficiency and enhance precision. Full article

Carbon dots (CDs) derived from mandarin peel biochar (MBC) at different pyrolysis temperatures (200, 400, 600, and 800 °C) have been synthesized and characterized. This high-value transformation of waste materials into fluorescent nanoprobes for environmental monitoring represents a step forward towards a circular economy. In this itinerary, CDs produced via one-pot hydrothermal synthesis were utilized for the detection of copper (II) ions. The study looked at the spectroscopic features of biochar-derived CDs. The selectivity of CDs obtained from biochar following carbonization at 400 °C (MBC400-CDs towards various heavy metal ions resulted in considerable fluorescence quenching with copper (II) ions, showcasing their potential as selective detectors. Transmission electron microscopic (TEM) analysis validated the MBC-CDs’ consistent spherical shape, with a particle size of <3 nm. The Plackett–Burman Design (PBD) was used to study three elements that influence the F₀/F ratio, with the best ratio obtained with a pH of 10, for 10 min, and an aqueous reaction medium. Cu (II) was detected over a dynamic range of 4.9–197.5 μM and limit of detection (LOD) of 0.01 μM. Validation testing proved the accuracy and precision for evaluating tap and mountain waters with great selectivity and no interference from coexisting metal ions. Full article

In this work, the properties of LiF crystals grown using Li of different isotopic compositions are described from the standpoint of their application as fluorescent nuclear track detectors used in measurements in the neutron radiation fields. The crystals were grown using two techniques: the Czochralski method and the micro-pulling-down method. Three isotopic compositions of Li were studied: natural, highly enriched in ⁶Li, and highly enriched in ⁷Li. It was found that ⁶LiF detectors are about six times more sensitive to thermal (low energy) neutrons than natural LiF, which significantly decreases the lower detection limit. ⁷LiF detectors are insensitive to thermal neutrons, which makes it easier to detect tracks due to other radiation modalities, such as energetic ions or nuclei recoiled in collisions with high-energy neutrons. Besides the response to neutron radiation, no other significant differences in the crystal properties were identified, irrespective of the isotopic composition and crystal growth method employed. Full article

Experimental methods of single-molecule enzymology allow scientists to determine physicochemical properties of distinct single molecules of various enzymes and to perform direct monitoring of functioning of enzymes at different steps of their catalytic cycle. The approach based on the use of solid-state nanopores is a promising tool for studying the functioning of single-enzyme molecules. Herein, this approach is employed for monitoring the functioning of cytochrome P450 BM3, which represents a very convenient model of cytochrome P450-containing monooxygenase systems. A nanopore of ~5 nm in diameter has been formed in a 40 nm-thick silicon nitride chip by electron beam drilling (EBD), and a single molecule of the BM3 enzyme has been entrapped in the pore. The functioning of the enzyme molecule has been monitored by recording the time dependence of the ion current through the nanopore during the reaction of laurate hydroxylation. In our experiments, the enzyme molecule has been found to be active for 1500 s. The results of our research can be further used in the development of highly sensitive detectors for single-molecule studies in enzymology. Full article

The influence of the etching method on the occurrence of defect levels in InAs/InAsSb type-II superlattice (T2SLs) and MCT photodiode is presented. For both analyzed detectors, the etching process was performed by two methods: wet chemical etching and dry etching using an ion beam (RIE—reactive ion etching). The deep-level transient spectroscopy (DLTS) method was used to determine the defect levels occurring in the analyzed structures. The obtained results indicate that the choice of etching method affects the occurrence of additional defect levels in the MCT material, but it has no significance for InAs/InAsSb T2SLs. Full article

A group of EUV lines of H- and He-like ions of C provides excellent wavelength calibrations for a position-sensitive multichannel detector at a high-resolution spectrograph. We have exploited this setting for a series of spectra of highly charged Eu ions recorded at the Livermore SuperEBIT electron beam ion trap. A variation in the electron beam energy results in spectra with correspondingly staggered highest Eu ion charge states ranging from Na- through to Ni-like Eu ions. A number of spectral features can be identified from the literature, but the majority of line identifications need guidance from computations of simulated spectra on the basis of collisional-radiative models. For ions with more than two electrons in the valence shell, the typical computational results are of a markedly lower accuracy. We have applied the Flexible Atomic Code (FAC), which is capable of handling all our measured ions with reasonable accuracy. We look into the systematics of the deviation of the computed transition energies from the measured ones as a function of the electron number. Full article

In recent years, the enthusiasm for deep space missions has remained unabated, resulting in continuous advancements in the research field of space environment and particles. Many instruments carried on these missions have conducted detection of pickup ions (PUIs) in the solar system. For those instruments, simulation is an effective means and a crucial step for their performance optimization and future operation in-orbit. It holds great significance for the instrument’s in-orbit performance assessment, science operation optimization, and detection efficiency enhancement. In this paper, the traditional probability model and the Vasyliunas and Siscoe (V–S) model are used to generate the PUIs, which are the input for the simulation of the PUI detector. For further analysis, the numerical results of the simulation are processed to calculate the instrument’s geometric factor, mass resolution, and count rates. Then, two sets of experiments are carried out for the comparison of the traditional probability model and the V–S model. The results show that, for the simulation of the instrument in the design stage, the simulation results of the traditional probability model and the V–S model are not much different. However, for the simulation of the instrument performance in-orbit, the PUI data generated based on the V–S model gave a better result than those of the traditional probability model. This conclusion is of great significance for evaluating the detection ability of the PUI detector in future deep space explorations. Full article

A highly efficient and sensitive ion mobility spectrometry (IMS) system with laser desorption sampling was applied for rapid explosive detection using different surface materials. This portable IMS detector, powered by a battery, offers mobility and is suitable for use in the field or combat zones. The laser desorption (LD) sampling of common explosives (Trinitrotoluene—TNT; Dinitrotoluenes—DNTs; Hexogene—RDX; pentaerythritol tetranitrate—PETN; plastic explosives—Compound 4 (C-4) and Semtex) on a wide range of common surface materials, such as metal, ceramic, plastic, glass, drywall, paper, wood, and textiles, was studied. Successful detection was achieved on nearly all surfaces except flammable materials (paper, wood, and textiles). The limit of detection (LOD) was determined for each explosive and specific surface, demonstrating an impressive LOD of 7 ng/mm² for TNT. RDX, C-4, PETN, and Semtex achieved LOD values of 15 ng/mm², while DNTs showed an LOD of approximately 50 ng/mm². Full article

Advances in accelerator technology have enabled the use of exotic and intense radioactive ion beams. Enhancements to tracking detectors are necessary to accommodate increased particle rates. Recent advancements in digital electronics have led to the construction or planning of next-generation detectors. To conduct kinematically complete measurements, it is essential to track and detect all particles produced as a result of the reaction. Furthermore, the need for high-precision physics experiments has led to significant developments in the detector field. In recent years, highly efficient and highly granular tracking detectors have been developed. These detectors significantly enhance the physics programme at dedicated facilities. An overview of charged-particle tracking detectors in low-energy nuclear physics will be given. Full article

Time-resolved spectroscopic and electron–ion coincidence techniques are essential to study dynamic processes in materials or chemical compounds. For this type of analysis, it is necessary to have detectors capable of providing, in addition to image-related information, the time of arrival for each individual detected particle (“x, y, time”). The electronics capable of handling such sensors must meet requirements achievable only with time-to-digital converters (TDC) with a resolution on the order of tens of picoseconds and the use of a field-programmable gate array (FPGA) to manage data acquisition and transmission. This study introduces the design and implementation of an innovative TDC based on two FPGAs working symbiotically with different tasks: the first (AMD/Xilinx Artix^® 7) directly implements a TDC, aiming for a temporal precision of 12 picoseconds, while the second (Intel Cyclone^® 10) manages the acquisition and connectivity with the external world. The TDC has been optimized to operate on eight channels (+ sync) simultaneously but is potentially extendable to a greater number of channels, making it particularly suitable for coincidence measurements where it is necessary to temporally correlate multiple pieces of information from various measurement systems. Full article