Photoionization Method Research Articles

Calculating Radio Emissions of Positive Streamer Phenomena Using 3D Simulations

AbstractWe study radio emissions from positive streamers in air using 3D simulations, from which the radiated electric field is computed by solving Jefimenko’s equations. The simulations are performed at using two photoionization methods: the Helmholtz approximation for a photon density and a Monte Carlo method using discrete photons, with the latter being the most realistic. We consider cases with single streamers, streamer branching, streamers interacting with preionization and streamer‐streamer encounters. We do not observe a strong VHF radio signal during or after branching, which is confirmed by lab experiments. This indicates that the current inside a streamer discharge evolves approximately continuously during branching. On the other hand, stochastic fluctuations in streamer propagation due to Monte Carlo photoionization lead to more radio emission being emitted at frequencies of 100 MHz and above. Another process that leads to such high‐frequency emission is the interaction of a streamer with a weakly preionized region, which can be present due to a previous discharge. In agreement with previous work, we observe the strongest and highest‐frequency emission from streamer encounters. The amount of total energy that is radiated seems to depend primarily on the background electric field, and less on the particular streamer evolution. Finally, we present approximations for the maximal current along a streamer channel and a fit formula for a streamer's current moment.

Photoionization of hydrogen halides using the R-matrix method

Abstract In this study, we use the UK Molecular R-matrix (UKRMol) codes in the close-coupling approximation to examine the photoionization of hydrogen halides (hydrogen fluoride, hydrogen chloride, and hydrogen bromide). This article reports the total and partial photoionization cross sections for the X2Π, A2Σ+, and B2Σ+ ionic states of these halides. The calculated cross sections are compared with the available literature, which does not accurately represent the effective cross sections near the threshold region, which is dominated by the Rydberg series autoionization resonances converging to the A2Σ+ ionic state. There seems to have been minimal effort to investigate the Rydberg-bound states of these halides. Meanwhile, the R-matrix approaches have traditionally excelled at characterizing such studies. This indicates the effectiveness of this method for molecular photoionization as well as for understanding the resonant contribution to the photoionization cross sections. The detailed cross sections calculated comprise the complex autoionizing resonance structures capable of significantly contributing to the computations of total photoionization rates, which are necessary to maintain a steady state of ionization in astrophysical plasmas. Comparisons with the experimental measurements and the theoretical data generally show reasonable agreement across the reported energy range.

Optimized laser photoionization scheme of separation of complex isotopes in the separator devices

An effective approach to determining parameters of optimal schemes of the method of laser selective photoionization of heavy isotopes, in particular, lanthanides (Gd atoms as the example) with ionization at the final stage by a pulsed electric field, autoionization through the narrow autoionization resonances and due to collisions is developed for separation of heavy isotopes in the separator devices. On the basis of the theory of optimal control and previously developed theoretical quantum approaches (the energy formalism and the relativistic many-body perturbation theory with the Dirac-Kohn-Sham-Sturm zeroth approximation for computing the parameters of elementary atomic processes such as excitation, ionization amplitudes, cross-sections, energies, widths of autoionization resonances etc.) an optimized scheme for the separation of Gd isotopes by the method of 3-stage laser photoionization with ionization at the final stage by a pulsed electric field, ionization through narrow autoionization resonances is presented. For the first time, there are theoretically calculated parameters of the narrow autoionization resonances for Gd in a sufficiently weak electric field, which are in physically reasonable agreement with data of the known experiment by Letokhov et al. Narrow-width autoionization resonances in Gd (in general in spectra of any lanthanide & actinide atom) have a relatively long lifetime, correspondingly, their excitation, ionization cross sections have the same order as the excitation one at the initial stage of separation scheme. Therefore, the use of these long-lived states can ensure the optimal implementation of a laser scheme for the separation of heavy isotopes. The obtained results for Gd with using models of optimal governing confirm the perspective of construction of the optimized schemes of the laser photoionization method with ionization at the final stage by a pulsed electric field, autoionization and allow determining the optimal parameters of the separation scheme, including diagram of atomic transitions, shape of laser pulses, etc. It is hoped that this work will also provide new opportunities for further development of laser chemistry of lanthanides, as well as actinides, taking into account new physics of autoionization resonances in their spectra.

Resonance ionization spectrum of autoionization states of lutetium atom

<sup>177</sup>Lu is an important medical isotope used in imaging-guided radiotherapy, and it can be produced by irradiating <sup>176</sup>Lu or <sup>176</sup>Yb with high abundance. With an increasing demand for medical isotopes, it is very essential to improve the supply capacity for <sup>177</sup>Lu. The multi-step multi-color photoionization method is an effective method to obtain isotopes, and the information of odd-parity autoionization levels is essential. Laser resonance ionization spectroscopy is one of a few spectroscopic experimental methods that can study autoionization levels. An experimental system is developed for the frontier spectroscopic research, and it consists of custom-made tunable lasers and a high-resolution time of flight mass spectrometer. The lifetime of the excited state 35274.5 cm<sup>–1</sup> is measured to be (31.6 ± 1.7) ns by the delayed photoionization method for the first time. A three-step three-color photoionization process is used to detect the autoionization levels, with a delay of 30 ns between <i>λ</i><sub>2</sub> – <i>λ</i><sub>1</sub> and <i>λ</i><sub>3</sub> – <i>λ</i><sub>2</sub> respectively, in order to avoid any unexpected transitions. Forty-seven odd-parity autoionization levels are obtained, of which 33 levels are discovered for the first time, and the <i>λ</i><sub>2</sub> and <i>λ</i><sub>1</sub> are blocked to exclude possible interference peaks, such as the <i>λ</i><sub>1</sub>+<i>λ</i><sub>3</sub>+<i>λ</i><sub>3</sub> transition. Several autoionization levels show asymmetrical peak shapes, and the Fano fitting is carried out for all the levels to determine the widths and relative transition strengths of the autoionizing transitions. This study provides critical data for the high-efficient photoionization of lutetium atoms in the visible range. The angular momenta of 21 odd-parity autoionization levels in an energy range of 50650–51650 cm<sup>–1</sup> are identified for the first time, which provides a reference for determining the forbidden state of electric dipole transitions from other excited states and ascertaining the electronic configuration.

A New Statistical Distance Scale for Planetary Nebulae, Based on Gaia EDR3

The present work aims to build a new statistical distance scale for planetary nebulae (PNe) based on a rigorous calibration sample. The distances of the calibration sample are derived from the trigonometric parallax method using the recent measurements of Gaia Early Data Release 3 (Gaia EDR3). The new distance scale is created by applying the well-known linear relationship between the radio surface brightness temperature and the nebular radius. The calibration sample is made up of 96 PNe of accurately computed distances with uncertainties less than 20%. Earlier ground- and space-based trigonometric parallaxes of PNe display inconsistency with those of Gaia, particularly the Hipparcos results. In addition, these measurements have appreciably lower precision than those of Gaia. When compared to the trigonometric technique, the expansion and kinematic methods exhibited more consistency than the spectroscopic, extinction, gravity, and photoionization methods. Furthermore, contrary to earlier results in the literature, the extinction and gravity methods, on average, underestimate and slightly overestimate the PN distances respectively. As a byproduct of extracting the Gaia parallaxes, we detect the radial velocity and variability for 14 and 3 PN central stars (CSs), respectively. To our knowledge, the variability of Hen 2-447 CS has been determined for the first time.

Analysis of RABITT time delays using the stationary multiphoton molecular R -matrix approach

We employ the recently developed multiphoton $R$-matrix method for molecular above-threshold photoionization to obtain second-order ionization amplitudes that govern the interference in RABITT experiments. This allows us to extract RABITT time delays that are in better agreement with nonperturbative time-dependent simulations of this process than the typically used combination of first-order (Wigner) delays and asymptotic corrections. We calculate molecular-frame as well as orientation-averaged RABITT delays for ${\mathrm{H}}_{2}, {\mathrm{N}}_{2}, {\mathrm{CO}}_{2}, {\mathrm{H}}_{2}\mathrm{O}$, and ${\mathrm{N}}_{2}\mathrm{O}$ and analyze the origin of various structures in the time delays including the effects of partial-wave interference, shape resonances, and orientation averaging. Time delays for B and C states of ${\mathrm{CO}}_{2}{}^{+}$ are strongly affected by absorption of the second (IR) photon in the ion. This effect corresponds to an additional contribution ${\ensuremath{\tau}}_{\text{coupl}}$ to the asymptotic approximation for the RABITT delays $\ensuremath{\tau}\ensuremath{\approx}{\ensuremath{\tau}}_{\text{mol}}+{\ensuremath{\tau}}_{cc}+{\ensuremath{\tau}}_{\text{coupl}}$. Applicability of the asymptotic theory depends on the target and IR photon energy but typically starts at approximately 30--35 eV of XUV photon energy.

Nitrous acid in high-pressure oxidation of CH4 doped with nitric oxide: Challenges in the isomer-selective detection and quantification of an elusive intermediate

The nitrous acid combustion intermediate has recently been detected in several reaction conditions using hydrocarbon fuels with different analytical techniques. Three of the several isomers of nitrous acid are expected to be produced during combustion: trans-HONO, cis-HONO and HNO2. It has recently been shown that cis-HONO dissociates upon ionization, rendering isomer selective quantification with methods requiring photoionization prior to detection impossible. This fact is of importance, since cis-HONO is produced at a ten times higher rate than trans-HONO according to recently published isomer branching ratios, possibly leading to sensitivity issues when a detection of the isomer mix is attempted with photoionization methods. We provide a quantitative glimpse at the trans-HONO isomer in a systematic set of measurements of NO doped methane oxidized in a plug-flow reactor covering three reaction conditions in the lean and rich regimes. Reactions take place at equivalence ratios of 0.7 and 1.2 with 1000 ppm NO and at an equivalence ratio of 2.1 doped with 1% NO. Double imaging photoelectron photo ion coincidence spectroscopy, i2PEPICO, was used to selectively and assuredly detect and assign trans-HONO. We touch on the difficulties encountered when attempting to detect cis-HONO. HNO2 remained undetectable despite recently published reaction rates for HNO2 decomposition suggesting modelled concentrations of this species two orders of magnitude larger than previously believed, yet 10 times lower than the reported isomer branching ratio. The recent reaction rates add a new path for HNO2 decomposition leading to formation of OH and NO which in turn influences the remaining decomposition kinetics of HNO2. A literature model is modified to include the recently published reaction rates for HONO and HNO2 decomposition and isomerization and compared to the measurements. Despite the higher predicted concentration of HNO2, that should be sufficient for detection, no HNO2 is detected in the experiment. Other nitrogen containing species, such as nitromethane and NO2, the precursor of both HONO and nitromethane, have also been detected. Interestingly, ammonia was also present in significant concentration, albeit exclusively in the fuel-rich conditions, despite the relatively low maximum temperature of 923 K at which the experiments have been performed. We conclude that, facing the unfavorable photoionization properties of cis-HONO as well as the decomposition and formation kinetics of HNO2, a measurement of isomer branching fractions by means of selective and sensitive photoionization methods may remain unattainable.

Isotope-selective laser ablation ion-trap loading of Ba+137 using a BaCl2 target

The $^{133}\mathrm{Ba}^+$ ion is a promising candidate as a high-fidelity qubit, and the $^{137}\mathrm{Ba}^+$ isotope is promising as a high-fidelity qudit ($d>2$). Barium metal is very reactive, and $^{133}\mathrm{Ba}^+$ is radioactive and can only be sourced in small quantities, so the most commonly used loading method, oven heating, is less suited for barium, and is currently not possible for $^{133}\mathrm{Ba}^+$.Pulsed laser ablation solves both of these problems by utilizing compound barium sources, while also giving some distinct advantages, such as fast loading, less displaced material, and lower heat load near the ion trap. Because of the relatively low abundances of the isotopes of interest, a two-step photoionization technique is used, which gives us the ability to selectively load isotopes. Characterization of the ablation process for our $\mathrm{BaCl}_2$ targets are presented, including observation of neutral and ion ablation-fluence regimes, preparation/conditioning and lifetimes of ablation spots, and plume velocity distributions.We show that using laser ablation on $\mathrm{BaCl}_2$ salt targets with a two-step photoionization method, we can produce and trap barium ions reliably. Further, we demonstrate that with our photoionization method, we can trap $^{137}\mathrm{Ba}^+$ with an enhanced selectivity compared to its natural abundance.

Quantitative analysis of polycyclic aromatic hydrocarbons using high-performance liquid chromatography-photodiode array-high-resolution mass spectrometric detection platform coupled to electrospray and atmospheric pressure photoionization sources.

Polycyclic aromatic hydrocarbons (PAHs) are common pollutants present in atmospheric aerosols and other environmental mixtures. They are of particular air quality and human health concerns as many of them are carcinogenic toxins. They also affect absorption of solar radiation by aerosols, therefore contributing to the radiative forcing of climate. For environmental chemistry studies, it is advantageous to quantify PAH components using the same analytical technics that are commonly applied to characterize a broad range of polar analytes present in the same environmental mixtures. Liquid chromatography coupled with photodiode array and high-resolution mass spectrometric detection (LC-PDA-HRMS) is a method of choice for comprehensive characterization of chemical composition and quantification of light absorption properties of individual organic compounds present in the environmental samples. However, quantification of non-polar PAHs by this method is poorly established because of their imperfect ionization in electrospray ionization (ESI) technique. This tutorial article provides a comprehensive evaluation of the quantitative analysis of 16 priority pollutant PAHs in a standard reference material using the LC-MS platform coupled with the ESI source. Results are further corroborated by the quantitation experiments using an atmospheric pressure photoionization (APPI) method, which is more sensitive for the PAH detection. The basic concepts and step-by-step practical guidance for the PAHs quantitative characterization are offered based on the systematic experiments, which include (1) Evaluation effects of different acidification levels by formic acid on the (+)ESI-MS detection of PAHs. (2) Comparison of detection limits in ESI+ versus APPI+ experiments. (3) Investigation of the PAH fragmentation patterns in MS2 experiments at different collision energies. (4) Calculation of wavelength dependent mass absorption coefficient (MACλ) of the standard mixture and its individual PAHs using LC-PDA data. (5) Assessment of the minimal injected mass required for accurate quantification of MACλ of the standard mixture and of a multi-component environmental sample.

Primary and Secondary Emissions of VOCs and PAHs in Indoor Air from a Waterproof Coal-Tar Membrane: Diagnosis and Remediation

Primary and secondary emissions of volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs) from a waterproof coal tar membrane and their effect on the indoor air quality were investigated through a case study in a residential building situated in Madrid, Spain. The air contaminants were analyzed in situ using photoionization method and several samples of contaminants were taken using three sorbents: activated carbon, XAD2 and Tenax GR. It was found that various VOCs such as toluene, p- and m-Xylene, PAHs such as naphthalene, methyl-naphthalenes, acenaphthene, acenaphthylene, phenanthrene and fluorine, volatile organic halogens including chloroform and trichlorofluoromethane, and alkylbenzene (1,2,4-trimethylbenzene) were found at concentrations, which exceeded the limits established by international and national agencies (WHO, EPA, OSHA). Some of the above organic compounds were found also in the samples of construction and building materials, which were obtained at different heights and places. The analysis of possible sources of the contaminants pointed at the original coal-tar membrane, which was applied on the terrace to be waterproof. During a posterior reparation the membrane was coated with a new one that hindered dissipation of emitted contaminants. The contaminants leached out and were absorbed by construction materials down in the dwelling. These materials then acted as secondary emission sources. To remediate the emission problem as the contaminated materials were removed and then a ventilation system was installed to force the gasses being emitted from the rest of contaminated slab outside. Follow-up has validated the success of the remediation procedure.

Advanced Laser-Photoionization Scheme of Separation of Heavy Isotopes in the Gases Separator Devices

An effective approach to determining the parameters of the optimal schemes of the method of laser selective photoionization of atoms (elements and isotopes) with finite ionization due to collisions, ionization by a pulsed electric field, ionization through high (Rydberg) states and narrow autoionization resonances for the separation of heavy isotopes has been proposed. in gas separator devices. On the basis of the theory of optimal control and previously developed quantum models for calculating the characteristics of elementary atomic processes, optimization models of isotope separation are numerically implemented in the scheme of selective laser photoionization with ionization due to collisions in gas mixtures, ionization by a pulsed electric field, autoionization, etc. etc. The data obtained quantitatively confirm the promise of the method of laser photoionization with finite ionization due to collisions, ionization by a pulsed electric field, ionization through high-lying (Rydberg) states and narrow autoionization resonances and give a set of parameters for the desired optimal schemes, in particular, the laser pulse optimal shape for rubidium and uranium isotopes.

The CaFe project: Optical Fe II and near-infrared Ca II triplet emission in active galaxies: simulated EWs and the co-dependence of cloud size and metal content

Aims. Modelling the low-ionisation lines (LILs) in active galactic nuclei (AGNs) still faces problems in explaining the observed equivalent widths (EWs) when realistic covering factors are used and the distance of the broad-line region (BLR) from the centre is assumed to be consistent with the reverberation mapping measurements. We re-emphasise this problem and suggest that the BLR ‘sees’ a different continuum from that seen by a distant observer. This change in the continuum reflected in the change in the net bolometric luminosity from the AGN is then able to resolve the above problem. Methods. We carefully examine the optical Fe II and near-infrared (NIR) Ca II triplet (CaT) emission strengths with respect to Hβ emission using the photoionisation code CLOUDY and a range of physical parameters. Prominent among these parameters are (a) the ionisation parameter (U), (b) the local BLR cloud density (nH), (c) the metal content in the BLR cloud, and (d) the cloud column density. Using an incident continuum for I Zw 1 –a prototypical Type-1 narrow-line Seyfert galaxy– our basic setup is able to recover the line ratios for the optical Fe II (i.e. RFeII) and for the NIR CaT (i.e. RCaT) in agreement with the observed estimates. Nevertheless, the pairs of (U,nH) that reproduce the conforming line ratios do not relate to agreeable line EWs. We therefore propose a way to mitigate this issue. The LIL region of the BLR cloud does not see the same continuum emitted by the accretion disc as that seen by a distant observer; rather it sees a filtered version of the original continuum which brings the radial sizes into agreement with the reverberation mapped estimates for the extension of the BLR. This is achieved by scaling the radial distance of the emitting regions from the central continuum source using the photoionisation method in correspondence with the reverberation mapping estimates for I Zw 1. Taking inspiration from past studies, we suggest that this collimation of the incident continuum can be explained by the anisotropic emission from the accretion disc, which modifies the spectral energy distribution such that the BLR receives a much cooler continuum with a reduced number of line-ionising photons, allowing reconciliation in the modelling with the line EWs. Results. (1) The assumption of the filtered continuum as the source of BLR irradiation recovers realistic EWs for the LIL species, such as the Hβ, Fe II, and CaT. However, our study finds that to account for the adequate RFeII (Fe II/Hβ flux ratio) emission, the BLR needs to be selectively overabundant in iron. On the other hand, the RCaT (CaT/Hβ flux ratio) emission spans a broader range from solar to super-solar metallicities. In all these models, the BLR cloud density is found to be consistent with our conclusions from prior studies, that is, nH ∼ 1012 cm−3 is required for the sufficient emission of Fe II and CaT. (2) We extend our modelling to test and confirm the co-dependence between metallicity and cloud column density for these two ionic species (Fe II and CaT), further allowing us to constrain the physical parameter space for the emission of these LILs. Adopting the estimates from line ratios that diagnose the metallicity in these gas-rich media –which suggest super-solar values (≳5−10 Z⊙)–, we arrive at cloud columns that are of the order of 1024 cm−2. (3) Finally, we test the effect of inclusion of a micro-turbulent velocity within the BLR cloud and find that the Fe II emission is positively affected. An interesting result obtained here is the reduction in the value of the metallicity by up to a factor of ten for the RFeII cases when the microturbulence is invoked, suggesting that microturbulence can act as an apparent metallicity controller for the Fe II. On the contrary, the RCaT cases are relatively unaffected by the inclusion of microturbulence.

Experimental validation of theoretically predicted cut-off of L1–L3M4,5 transitions at Z = 50 through measurements of fluorescence and Coster–Kronig yields for Sn and Sb

In the present work, we have deduced the fluorescence (ω 1, ω 2, ω 3) and Coster–Kronig (CK)(f 12, f 13, f 23) yields for Sn (Z = 50) and Sb (Z = 51) from the L i (i = 1–3) sub-shell x-ray intensities measured using the energy tunable synchrotron radiation employing the selective photoionization method. For both the elements, yields have been obtained using two sets of theoretical photoionization cross sections based on the non-relativistic Hartree–Fock–Slater (HFS) model and the self-consistent Dirac–Hartree–Fock (DHF) model. In case of Sb, we have obtained a third set of measured yields also by using the experimental photoionization cross sections evaluated from independent measurements of the mass-attenuation coefficients. The experimental yields for Sb are reported for the first time by us. We have compared the present deduced fluorescence and CK yields with the Dirac–Hartree–Slater model based values, the semi-empirical values tabulated by Krause and the earlier reported values. In case of Sn, using the DHF and the HFS model based photoionization cross sections, two sets of present measured L1 sub-shell fluorescence yields (ω 1) are found to be 0.039 ± 0.007 and 0.036 ± 0.003, and the CK yields (f 13) are found to be 0.428 ± 0.107 and 0.405 ± 0.028, respectively. In case of Sb, using three sets of the photoionization cross sections (DHF, HFS and recent experimental values), the ω 1 values are measured to be 0.042 ± 0.007, 0.040 ± 0.004 and 0.047 ± 0.005, and the CK yields are measured to be 0.343 ± 0.085, 0.297 ± 0.021 and 0.247 ± 0.022, respectively. The comparison of these present measured yields with the theoretical values provided a reliable experimental evidence indicating cut-off of the intense L1–L3M4,5 CK transitions at Z = 50.

Principle and technology of attosecond pulse characterization

Attosecond pulses have potential applications in the fields of physics, chemistry, biology, and medicine owing to the extremely high time resolution brought by their extremely short pulse widths. The generation and measurement technology of attosecond pulses provides a powerful means for the study of electron dynamical process in atoms. Since the date of its birth, the time width of an attosecond pulse has become shorter and shorter, making its measurement a challenging task. Although attosecond pulses are more and more widely used in the study of ultrafast dynamics and more interest is attracted into the field of attosecond science, it is undeniable that there are still difficulties and challenges for the measurement of attosecond pulses. This review is divided into two parts. The first part presents the development of technics for characterizing attosecond pulses, and briefly describes several experimental principles, setups and results for acquiring time-domain information of attosecond pulses, including RABITT (reconstruction of attosecond beating by interference of two-photon transitions) and laser-assisted lateral X-ray photoionization for measuring attosecond pulse train, attosecond streak camera for measuring single attosecond pulses, TIPTOE (tunneling ionization with a perturbation for the time-domain observation of an electric field) for measuring time-domain information of periodic pulses, as well as theoretical proposals such as attosecond cross correlation, asymmetric photoionization method, and SPIDER (attosecond spectral phase interferometry for direct electric-field reconstruction). The second part introduces the principle and structure of inversion algorithms for extracting time-domain information of attosecond pulses from spectrograms obtained with an attosecond streak camera, including FROG-CRAB (frequency resolved optical gating for complete reconstruction of attosecond bursts), PROOF (phase retrieval by omega oscillation filtering), VTGPA (Volkov transform generalized projections algorithm), PROBP-AC (phase retrieval of broadband pulses with autocorrelation) and CVGN (conditional variational generative network). We also evaluate the calculation time and accuracy of the algorithms. Finally, we summarize the experimental and theoretical challenges of the characterization of attosecond pulses, and look forward to the future development of attosecond pulse measurement.

Time-of-flight mass spectrometric diagnostics for ionized and neutral species in high-power pulsed magnetron sputtering of titanium

A photoionization method using a vacuum ultraviolet laser was applied to the time-of-flight mass spectrometry of ions formed in high-power pulsed magnetron sputtering (HPPMS). This method is a new plasma diagnostic technique for measuring simultaneously the amounts of sputtered ionized and neutral species in HPPMS. The temporal profiles for the amounts of ions and neutrals were observed with respect to the trigger of the pulsed discharge in HPPMS. This result is discussed in connection with the atomic processes of light-emitting ionized and neutral species measured in optical emission spectroscopy for HPPMS.

A Study of the Kinetic Parameters of Lu Laser Photoionization Scheme

Development of the laser photoionization method for obtaining 177Lu radionuclide for a medical purpose requires the knowledge of the light-saturation intensities at each stage of the Lu photoionization scheme (5d6s22D3/2−5d6s6p4F$$_{{5/2}}^{^\circ }$$−5d6s7s4D3/2−(53 375 cm–1)$$_{{1/2}}^{^\circ }$$), taking into account the used components of the hyperfine structure of transitions. The effective excitation cross sections of various hyperfine transition components for 175Lu, 176Lu, 177Lu, and 177mLu isotopes have been experimentally determined for radiations of pulsed tunable dye lasers pumped by copper-vapor lasers.

CHARACTERIZATION OF VOLATILE ORGANIC COMPOUNDS AND ODOUR POLLUTION IN ATMOSPHERE AT OIL AND GASOLINE HANDLING AND PROCESSING IMPACT ZONE

Air quality pollution problem is still one of the crucial points for citizens in Europe for already receiving increasing attention, particularly because of the major European cities 10 and more years. Although the EU's long-term goal is to achieve levels of air quality that do not impact and risks to human health and the environment, many of member states still didn`t reach stated goals. Additionally, to gaseous pollutants, recently specific type of pollution, - odour, seems to become more important. Usually in order to determine pollution levels, national, municipal and private monitoring equipment is used. For this research municipal monitoring site in Riga (Latvia), at Milgravja Street 10, controlling gaseous pollutants (SO2, O3, BTX, PM10) and airborne particulate matter, and private monitoring results from Riga, Milgravja Street 16, where odour pollution was obtained, are analysed. Distance between both stations are just 500 m. Measurements at municipal monitoring site is obtained by DOAS and gravimetric sampling, while at Milgravja 16 by photoionization method or so-called “electronic nose”. Monitoring results in municipal station show that in 2017 the average benzene concentration was 4,87 ug/m3, toluene – 8,89 ug /m3 and xylene – 5,07 ug/m3, while the odour pollution level does not exceed 5 odour units. In general estimation of pollution averaged annually do not show and explain variability of pollution levels. It`s well known that high BTX and odour pollution episodes occur in shorter periods, thus short term limit values would be useful in order to characterize short term effects on human health and well-being.

SDSS-IV/SPIDERS: A catalogue of X-ray selected AGN properties

This work presents the catalogue of optical spectral properties for all X-ray selected SPIDERS active galactic nuclei (AGN) up to SDSS DR14. SPIDERS (SPectroscopic IDentification of eROSITA Sources) is an SDSS-IV programme that is currently conducting optical spectroscopy of the counterparts to the X-ray selected sources detected in the ROSAT all-sky survey and the XMM-Newton slew survey in the footprint of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS). The SPIDERS DR14 sample is the largest sample of X-ray selected AGN with optical spectroscopic follow-up to date. The catalogue presented here is based on a clean sample of 7344 2RXS (z¯ = 0.5) and 1157 XMM-Newton slew survey (z¯ = 0.4) type 1 AGN with spectroscopic coverage of the Hβ and/or MgII emission lines. Visual inspection results for each object in this sample are available from a combination of literature sources and the SPIDERS group, which provide both reliable redshifts and source classifications. The spectral regions around the Hβ and MgII emission lines have been fit in order to measure both line and continuum properties, estimate bolometric luminosities, and provide black hole mass estimates using the single-epoch (or photoionisation) method. The use of both Hβ and MgII allows black hole masses to be estimated up to z ≃ 2.5. A comparison is made between the spectral properties and black hole mass estimates derived from Hβ and MgII using the subsample of objects which have coverage of both lines in their spectrum. These results have been made publicly available as an SDSS-IV DR14 value added catalogue.

The effect of the stochasticity of photoionization on 3D streamer simulations

Positive streamer discharges require a source of free electrons ahead of them for their growth. In air, these electrons are typically provided by photoionization. Here we investigate how stochastic fluctuations due to the discreteness of ionizing photons affect positive streamers in air. We simulate positive streamers between two planar electrodes with a 3D plasma fluid model, using both a stochastic and a continuum method for photoionization. With stochastic photoionization, fluctuations are visible in the streamer’s direction, maximal electric field, velocity, and electron density. The streamers do not branch, and we find good agreement between the averaged stochastic results and the results with continuum photoionization. The streamers stay roughly axisymmetric, and we show that results obtained with an axisymmetric model indeed agree well with the 3D results. However, we find that positive streamers are sensitive to the amount of photoionization. When the amount of photoionization is doubled, there is even better agreement between the stochastic and continuum results, but with half the amount of photoionization, stochastic fluctuations become more important and streamer branching starts to occur.

Experimental study of the degree of extraction of a target isotope in the process of laser photoionisation separation of lutetium isotopes

The degree of target isotope extraction is studied in application to the problem of extracting the radioisotope 177Lu by means of the laser photoionisation method using the developed high-efficiency three-stage scheme 5d6s2 2D3/2–5d6s6p 4D3/2–53375.049 cm−1.