Atomic Isotope Research Articles

Continuous wave dual-wavelength Nd:YVO4 laser at 1342 and 1525 nm for generating a 714-nm emission

Continuous wave dual-wavelength lasers at 1342 and 1525 nm are developed by using separate Nd:YVO4 and YVO4 crystals to form compactly coupled cavities for fundamental and Raman waves, respectively. The design of the coupled cavity not only reduces the thermal lensing effect in the Nd:YVO4 crystal, but also improves the stimulated Raman scattering (SRS) efficiency in the undoped YVO4 crystal. In addition, the Raman crystal is coated to form a highly reflective mirror to minimize cavity losses. By using a plano-concave cavity with a pump power of 40 W, the output powers of the fundamental and Raman waves are 470 mW and 310 mW, respectively. Changed to a concave cavity, the output powers of fundamental and Raman waves are 220 mW and 510 mW, respectively. Basis on the dual-wavelength operation, the maximum output power at 714 nm can reach 2.0 W via the sum frequency generation. A light source at 714 nm can be used for laser spectroscopy of atomic and ionic radium isotopes.

Isotope shift factors for theCd+5s2S1/2→5p2P3/2transition and determination of Cd nuclear charge radii

The accuracy of atomic isotope shift factors limits the extraction of nuclear charge radii from isotope shift measurements because determining these factors is experimentally and theoretically challenging. Here, the isotope shift of the ${\mathrm{Cd}}^{+}\phantom{\rule{4pt}{0ex}}5s{\phantom{\rule{0.16em}{0ex}}}^{2}{S}_{1/2}\ensuremath{\rightarrow}5p{\phantom{\rule{0.16em}{0ex}}}^{2}{P}_{3/2}$ transition is measured precisely using laser-induced fluorescence from a sympathetically cooled large ${\mathrm{Cd}}^{+}$ ion crystal. A King-plot analysis is performed based on the new measurement to obtain accurate atomic field shift $F$ and mass shift $K$ factors that have been cross-checked by state-of-the-art configuration interaction plus many-body perturbation theory. The nuclear charge radii (${R}_{\mathrm{ch}}$) of $^{100\text{--}130}\mathrm{Cd}$ extracted using these $F$ and $K$ values demonstrate a near fivefold precision increase in the neutron-rich region. This work proves that accurate extraction of ${R}_{\mathrm{ch}}$ from isotope shifts is possible. New ${R}_{\mathrm{ch}}$ values reveal hidden discrepancies with previous density functional predictions in the neutron-rich region and pose strong challenges to advancements in nuclear models.

Doppler-dependent fluorescence spectroscopy of Yb atomic gas for trapped-ion experiments

An ion trap-based Quantum system has been one of the leading architectures toward building a scalable and practical quantum computer. The trapped ion system also has been used for precision experiments such as quantum sensing, metrology, and atomic clock. For the ion-trap experiment, searching resonant frequencies of atomic isotopes are essential for selectively ionization and trapping a specific isotope. In this work, we set up an Yb fluorescence spectroscopy for detecting 399 nm photons of 1S0 → 1P1 transition of the Yb gas from a heated oven. We observed the relative frequency differences between the Yb isotopes and calibrated an optical wavemeter comparing with previous literatures. In addition, we obtain characteristic properties of the atomic oven such as gas’ velocity and density distribution at different oven temperatures. Our experiment can offer a relatively simple and cost-efficient apparatus of spectroscopy and can be useful for designing trap devices in the trapped-ion experiment.

Structural Modifications as Tools in Mechanistic Studies of the Cleavage of RNA Phosphodiester Linkages.

The cleavage of RNA phosphodiester bonds by RNase A and hammerhead ribozyme at neutral pH fundamentally differs from the spontaneous reactions of these bonds under the same conditions. While the predominant spontaneous reaction is isomerization of the 3',5'-phosphodiester linkages to their 2',5'-counterparts, this reaction has never been reported to compete with the enzymatic cleavage reaction, not even as a minor side reaction. Comparative kinetic measurements with structurally modified di-nucleoside monophosphates and oligomeric phosphodiesters have played an important role in clarification of mechanistic details of the buffer-independent and buffer-catalyzed reactions. More recently, heavy atom isotope effects and theoretical calculations have refined the picture. The primary aim of all these studies has been to form a solid basis for mechanistic analyses of the action of more complicated catalytic machineries. In other words, to contribute to conception of a plausible unified picture of RNA cleavage by biocatalysts, such as RNAse A, hammerhead ribozyme and DNAzymes. In addition, structurally modified trinucleoside monophosphates as transition state models for Group I and II introns have clarified some features of the action of large ribozymes.

Resonance Raman spectroscopy of pyranopterin molybdenum enzymes

Resonance Raman spectroscopy (rR) is a powerful spectroscopic probe that is widely used for studying the geometric and electronic structure of metalloproteins. In this focused review, we detail how resonance Raman spectroscopy has contributed to a greater understanding of electronic structure, geometric structure, and the reaction mechanisms of pyranopterin molybdenum enzymes. The review focuses on the enzymes sulfite oxidase (SO), dimethyl sulfoxide reductase (DMSOR), xanthine oxidase (XO), and carbon monoxide dehydrogenase. Specifically, we highlight how Mo-Ooxo, Mo-Ssulfido, Mo-Sdithiolene, and dithiolene CC vibrational modes, isotope and heavy atom perturbations, resonance enhancement, and associated Raman studies of small molecule analogs have provided detailed insight into the nature of these metalloenzyme active sites.

Anisotropic angular scattering models of elastic electron-neutral collisions for Monte Carlo plasma simulations

Many laboratory and industrial plasma applications require accurate modeling techniques to understand the interplay between microscopic and macroscopic processes. A prime example of this interplay is how particle and Monte Carlo (MC) simulation codes describe angular scattering of electrons following elastic scattering events. The forward peaked nature of high energy electron elastic scattering is relatively trivial to accurately describe in plasma simulations. However, for lower energy collisions, which produce near isotropic or backward peaked differential cross sections, there is not a strong consensus among the plasma modeling community on how to best describe these angular scattering trends. In this study, we propose a systematic method to approximate the aforementioned non-trivial angular scattering behavior with a formula that can be readily implemented in particle-in-cell (PIC) and/or MC plasma simulation codes. The present approach is specifically applied to fusion relevant atomic hydrogen and helium, as well as for molecular hydrogen, and results are also applicable to the atomic isotopes and homonuclear molecular isotopologues of these species. Comparisons between the present angular distribution function and benchmark scattering data were used to validate the proposed models. In addition, two-term Boltzmann calculations and PIC direct simulation MC simulations revealed that the proposed angular distribution function is accurate, agreeing very well with benchmark convergent close-coupling scattering calculations, and electron transport measurements. These studies confirmed that the present angular distribution function model can be utilized without the need of renormalization to the momentum transfer cross section (as opposed to using the elastic scattering integrated cross section), which has been suggested by several studies in order to correct for deficient angular scattering models, and to agree with transport measurements. Hence, the present anisotropic angular scattering model can be utilized to accurately model the momentum transfer as well as the electron trajectories of elastic collisions.

NORTH-EASTERN SHARED RESEARCH FACILITIES OF NEISRI FEB RAS: EQUIPMENT AND DIRECTIONS OF RESEARCH

The activity of the North-Eastern Shared Research Facilities of the Shilo North-East Interdisciplinary Scientific Research Institute, Far Eastern Branch of the Russian Academy of Sciences (NEISRI FEB RAS) is aimed at conducting analytical studies of rocks, minerals, ores, soils, lake and sea sediments, water bodies using various methods: optical microscopy, X-ray microanalysis, X-ray fluorescence analysis, quantitative emission spectral analysis, atomic absorption spectrometry, isotope geochronology, paleomagnetism and petromagnetism. The results of mineralogical, geochemical, petrophysical, isotope-geochronological (including radiocarbon) and palynological studies have been published in national and international scientific journals.

Proteomics Standards Initiative's ProForma 2.0: Unifying the Encoding of Proteoforms and Peptidoforms.

It is important for the proteomics community to have a standardized manner to represent all possible variations of a protein or peptide primary sequence, including natural, chemically-induced and artifactual modifications. The Human Proteome Organization (HUPO) Proteomics Standards Initiative (PSI) in collaboration with several members of the Consortium for Top-Down Proteomics (CTDP) has developed a standard notation called ProForma 2.0, which is a substantial extension of the original ProForma notation developed by the CTDP. ProForma 2.0 aims to unify the representation of proteoforms and peptidoforms.ProForma 2.0 supports use cases needed for bottom-up and middle-/top-down proteomics approaches and allows the encoding of highly modified proteins and peptides using a human-and machine-readable string. ProForma 2.0 can be used to represent protein modifications in a specified or ambiguous location, designated by mass shifts, chemical formulas, or controlled vocabulary terms, including cross-links (natural and chemical), and atomic isotopes. Notational conventions are based on public controlled vocabularies and ontologies. The most up-to-date full specification document and information about software implementations are available at http://psidev.info/proforma.

Matter radii and skins of [formula omitted]He from reaction cross section of proton+[formula omitted]He scattering based on the Love–Franey [formula omitted]-matrix model

Background:For 4,6,8He, Tanihata et al. determined matter radii rm(σI)=1.57(4),2.48(3),2.52(3) fm from interaction cross sections σI for 4,6,8He scattering on Be, C Al targets at 790 MeV/nucleon. Lu et al. measured the atomic isotope shifts (AIS) for 4,6,8He and determined proton radii rp(AIS) for 4,6,8He. As for p+4,6,8He scattering, reaction cross sections σR(exp) are available at 700 MeV with high accuracy. Aim:Our aim is to determine matter radii rm and skins rskin for 6,8He from the σR(exp) and the rp(AIS). Method:Our model is the Love–Franey t-matrix folding model, since the model is better than the optical limit of Glauber model. Results:Our results for 6,8He are rm(exp)=2.48(3),2.53(2) fm and rskin=0.78(3), 0.82(2) fm. Conclusion:For 6,8He, our results rm(σR) agree with those of Tanihata et al.. For 8He, the distance between 4He and the center of mass of valence four neutrons is 2.367 fm.

Folding-model approach to reaction cross section of [formula omitted]He+12C scattering at 790 MeV

Tanihata et al. (1988) determined matter radii rm(σI) for 4,6,8He from interaction cross sections σI of 4,6,8He+12C scattering at 790 MeV per nucleon, using the optical limit of the Glauber model. Lu et al. (2013) determined proton radii rp(AIS) for 4,6,8He with the atomic isotope shifts (AIS). We investigate whether the Love-Franey t-matrix folding model is good for 4,6,8He+12C scattering at 790 MeV per nucleon.

Методы получения поляризованного ксенона для магнитно-резонансной томографии (обзор)

A review of experimental studies and design developments of devices for obtaining nuclear-spin hyperpolarized 129Xe by optical pumping of rubidium vapor with subsequent spin exchange with noble gas isotope atoms is presented. Hyperpolarized 129Xe atom is an excellent probe in magnetic resonance imaging in studies of lung structure and function, and biomarkers based on it are applicable for the diagnosis of a wide range of both pulmonary and other diseases. The principles of operation, advantages and disadvantages of polarizer design options are outlined. The main attention is paid to new approaches and technical solutions that determine the trends in the development of the methodology.

RADIATIVE AND MAGNETICALLY STIMULATED CHANGE OF THE ELECTRICAL PROPERTIES OF THE SiO2-Si STRUCTURE WITH A HIGH CONTENT OF DISLOCATION COMPLEXES

The effect of various types of irradiation and magnetic field on the surface of the semiconductor is a relevant topic, since it is the change in the density of the SS that is responsible for the occurrence of sensitive (sensory) effects associated with dislocations adsorbed particles. The paper examines the effect of X-irradiation on the Si surface with different dislocation density (10 2 – 10 5 cm -2 ). The capacitance–voltage characteristics (CVC) of the Bi-SiO 2 -Si-Al structure indicate (their maxima) a sufficiently large charge in the dielectric layer of the capacity of this maximum. As the dislocation density increases, the capacitance value in the region of positive voltages decreases, which is associated with a decrease in the spatial charge region (SCR) value, as well as the distribution of the density of surface states in the band gap and their rate of recharging changes. To determine the density of surface states, the ideal (mathematically calculated) structures of Bi-SiO 2 -Si-Al (MOS) is compared with the real one. It is shown that the maximum concentration of SS is formed in the defect layers of the transition region, in which there are maximum mechanical stresses. The source of such stresses can be dislocations, which contribute to the energy spectrum of the surface. They increase the concentration of surface states in the depicted silicon zone by an order of magnitude. The spectrum becomes more complex with well-defined maxima in the energy range [from -0.1 to +0.4] eV at N ~ 10 5 cm -2 . This is due to the fact that, with low-energy irradiation of barrier structures in silicon oxide, the process of generation of electron-hole pairs occurs. The mobility of electrons in SiO 2 is much higher than the mobility of holes. Electrons that do not recombine leave the dielectric, holes (p + ) thermalize and fall to levels near the ceiling of the valence band. Thermal excitation of holes causes their capture at the level of tight bonds with a disturbance of equilibrium and the movement of atoms from the local to the free energy minimum. At the same time, the reaction takes place: ≡Si-O-Si≡ + p + →Si + +O 0 -Si≡ it shows the formation of "trivalent" silicon and "non-bridging" oxygen, which lead to the emergence of pseudovacancies, which lead to the accumulation of an additional charge in SiO 2 when the silicon structure is irradiated. In this case, the increase in the dislocation density enhances the effect of the radiation-stimulated SS change at the SiO 2 -Si interface. Under the action of X-irradiation on the surface of Si, there is a rearrangement of existing metastable defects and the formation of new ones, the increase in the density of which is associated with heterogeneity them from the volume semiconductor to the surface. They make a significant contribution to the SS spectrum. Upon irradiation, they can reorganize into more complex complexes with a change in SS. As a result of aging the structure Bi-SiO 2 -Si-Al in a magnetic field (MF) (B = 0.17 T) with different dislocation concentrations (terms of 4, 12, 20 days), the SS spectrum changes significantly. At N ≈ 10 4 – 10 5 cm -2 becomes monotonous after 20 days. The effect of a magnetic field on silicon does not cause the generation of electrically active defects in the near-surface layers of semiconductor, but promotes the rearrangement of oxygen and hydrogen complexes adsorbed on the surface, which are present on Si. It is they who determine the nature of the change in the SS due to the actions of the MF. Under the action of a magnetic field, a spin-dependent process of breaking chemical bonds in nanoclusters of structural defects (Si-H, Si-OH, -OH) occurs. As a result of breaking chemical bonds, hydrogen ions diffuse across the crystal and passivate acceptor and donor bonds. In addition, the action of MF leads to dynamic polarization of the nuclei of the Si 29 isotope atom and polarization of the electron spins in Si to the electron spins of oxygen due to the ultrathin interaction with polarized nuclei. A change in the orientation of the electron spin leads to the breakdown of the chemical bond. The effect of MF detection on non-magnetic materials, which are non-magnetic, is enhanced by prolonged exposure of samples to MF and the presence of defects in the near-surface layers. It is obvious that the presence of a dislocation will strengthen the influence of the MF on the change of the SS at the boundary SiO 2 -Si. Key words : silicon, magnetic field, X-irradiation, dislocations.

Methods for obtaining polarized xenon for magnetic resonance imaging. Review

A review of experimental studies and design developments of devices for obtaining nuclear-spin hyperpolarized 129Xe by optical pumping of rubidium vapor with subsequent spin exchange with noble gas isotope atoms is presented. Hyperpolarized 129Xe atom is an excellent probe in magnetic resonance imaging in studies of lung structure and function, and biomarkers based on it are applicable for the diagnosis of a wide range of both pulmonary and other diseases. The principles of operation, advantages and disadvantages of polarizer design options are outlined. The main attention is paid to new approaches and technical solutions that determine the trends in the development of the methodology. Keywords: hyperpolarized xenon, lasers, optical pumping, nuclear magnetic resonance, magnetic resonance imaging.

Isotope effect of rovibrational distribution of hydrogen molecules desorbed from amorphous carbon

When the hydrogen isotope atom is injected into the amorphous carbon with the incident energies E in of 20, 50, and 80 eV, we obtain the following physical quantities of hydrogen isotope atoms/molecules emitted from the amorphous carbon using molecular dynamics and heat conduction hybrid simulation. The physical quantities are the time evolution of the emission rate, the depth distribution of the original location of the hydrogen emitted from the target, the polar angular dependence, and the translational, rotational, and vibrational energy distributions. In addition, the approximate analysis yields the emission distributions at the vibrational (v) and rotational (J) levels. Using these distributions, we evaluate the rotational temperature T rot for v = 0 and small J states. From the above, it is found that molecules with higher rotational levels J tend to be emitted as E in increases or as the mass of hydrogen isotope increases. Moreover, the isotope effect appears in the mass dependence of T rot.

King and second-King plots with optimized sensitivity for lithium ions

King plots constructed from combinations of mass-weighted atomic isotope shifts provide a sensitive technique to search for electron-neutron interactions beyond the standard model mediated by a light boson. Using high-precision variational wave functions in Hylleraas coordinates, we present a comprehensive survey of all possible King plots arising from states of ${\mathrm{Li}}^{+}$ up to principal quantum number $n=10$ and angular momentum $L=7$ in order to identify the ones most sensitive to new physics. A major limitation in previous work due to second-order mass polarization is eliminated by the introduction of a second-King plot defined in terms of second differences. The residual theoretical uncertainty is then of the order of ${\ensuremath{\alpha}}^{2}{(\ensuremath{\mu}/M)}^{3}\ensuremath{\sim}0.4$ Hz, where $\ensuremath{\alpha}$ is the fine-structure constant and $\ensuremath{\mu}$ is the reduced electron mass for a nucleus of mass $M$. Test results are presented for the ${}^{A}{\mathrm{Li}}^{+}$ isotope sequence with $A=6,7,8,9,11$ and are compared with other methods, including the ${\mathrm{Yb}}^{+}$ case recently studied both experimentally and theoretically. It is shown that the second-King plots for ${\mathrm{Li}}^{+}$ have about the same sensitivity to new physics as the ${\mathrm{Yb}}^{+}$ case for boson masses up to about 10 keV, and nuclear size uncertainties (including nuclear polarization) are suppressed. This greatly extends the sensitivity to new physics for light two-electron systems.

Characterization of the negatively charged NV defect through the spin density distribution and the hyperfine coupling constants

The spin density function and hyperfine coupling constants of the NV− defect (a vacancy with one nitrogen atom as a first neighbor) in its triplet ground state, are computed by using hybrid functionals, a Gaussian type all electron basis set, the supercell scheme (216 atoms before the defect formation), and the CRYSTAL code. The charged defect has been simulated by using the charge compensated (CC) scheme, in which a background of positive charge is added to restore the neutrality of the unit cell. The local geometry, charge and spin distribution are also reported and discussed. The EPR constants (Fermi contact, the hyperfine coupling and electric field gradient tensors) of the N (both 14N and 15N) and of two C (for the 13C isotope) atoms around the vacancy are in excellent agreement with the recent experimental results by Felton et al. (Phys. Rev. B, 79,075 203, 2009). The comparison is extended to the many other experimental data collected in the last 30 years, to simpler functionals (LDA and PBE), larger supercells (512 atoms), and to recent simulations. It is shown that the present results are much closer to experiment than previous theoretical studies, with a quantitative, rather than qualitative, agreement.

Employing of ZrCo as a fuel source in a discharge-type fusion neutron source operated in self-sufficient mode

A discharge-type fusion neutron source generates neutrons by fusion reactions of hydrogen isotope atoms. In order to operate the fusion device based on the deuterium–tritium (D–T) fusion reaction, the tritium inventory is required to be decreased. In the present work, a self-sufficient system was installed into the fusion device for reducing the amount of hydrogen isotope fuel gas. The fuel gas was supplied and recovered with an intermetallic compound ZrCo in a sealed chamber in this system. A deuterium–deuterium operation was maintained for more than 60 min with stable discharge voltages, and the temperature of the ZrCo bed was changed to improve the neutron production rate. Factors that influenced the pressure inside the chamber were determined and optimized. Gas analysis using a quadrupole mass spectrometer indicates a dilution of the deuterium fuel was caused by hydrogen isotope exchange between the supplied deuterium gas and the absorbed protium on the chamber and electrodes surface. This system's hydrogen isotope control method and the amount of fuel were proposed for a D–T operation.

Moving an atom by swapping places across a crystal lattice without vacancies

The mechanism of moving an atom through a crystal lattice without vacancies is considered. This situation can be observed when all sites of the lattice are occupied by atoms of the same type, or when some of them are occupied by isotopes of the same atoms. It is shown that in a three-dimensional crystal lattice constructed from identical atoms without vacancies, one-dimensional motion of the own atom along the lattice chain is possible. This movement is realized as a Frenkel-Kontorova soliton.

Neutron-alpha reactions in nano α-Si3N4 particles by neutrons

Computer modeling was applied to the study of [Formula: see text] transmutations in [Formula: see text] nanoparticles under the influence of neutrons at different energies. The modeling was separately performed for each Si and N atoms in the [Formula: see text] nanoparticles and the effect of neutrons on transmutations was investigated. The simulations were conducted individually for each stable isotope due to different effective cross-section of the probability of transmutation in the different types of isotopes of silicon and nitrogen atoms. Effective cross-section spectra of [Formula: see text] transmutation in Si and N atoms were comparatively studied.

Inherent strains in chemical-vapor-deposited bilayer graphene on Cu

The electrical properties of bilayer graphene (BLG) are strongly affected by external forces. Here we use Raman spectroscopy to study the inherent strain states of BLG synthesized by chemical vapor deposition method on Cu, by manipulating 13C isotope atoms to substitute part of one layer in AB-stacked and twisted BLG to differentiate the Raman signals from the two layers. Results show that, both layers of twisted BLG are under compression but the compressive strain in the bottom layer is larger, which is caused by the mismatch of coefficients of thermal expansion between graphene and the substrate, whereas for AB-stacked BLG its top layer is under compression and the bottom layer is under tension due to the interlayer dislocations. These experimental data are further confirmed by molecular dynamics simulations. We believe that a clear understanding of the strain states of chemical-vapor-deposited BLG will provide the necessary route to optimize its future technologies especially in electronics.