Ionization equilibrium and radiative energy loss rates for C,N, and O ions in low-density plasmas

The results of calculations of the ionization equilibrium and radiative energy loss rates for C, N and O ions in low-density plasmas are presented for electron temperatures in the range 10⁴–10⁷ °K (～1–10³ eV). The ionization structure is determined using the steady-state corona model, in which electron impact ionization from the ground states is balanced by direct radiative and dielectronic recombination. Using an improved theory, detailed calculations are carried out for the dielectronic recombination rates in which account is taken of all radiative and autoionization processes involving a single-electron electricdipole transition of the recombining ion. The radiative energy loss processes considered are electron-impact excitation of resonance line emission, direct radiative recombination, dielectronic recombination, and electron-ion bremsstrahlung. For all three elements, resonance line emission resulting from 2s?2p transitions produces a broad maximum in the energy loss rate near 10⁵°K(～ 10 eV).     

Oscillator strengths and lifetimes of levels for ions of the rubidium isoelectronic sequence calculated by the Dirac-Fock method

The oscillator strengths f of the resonance transitions are calculated by the Dirac-Fock method for the first ten terms of the rubidium isoelectronic sequence. The variation of f values along the isoelectronic sequence is analyzed. The corresponding transition probabilities and lifetimes τ of the levels 5p ² P _1/2 and 5p ² P _3/2 are calculated. The dependence of τ on the ion charge is approximated by an analytical equation. The obtained values of f and τ are compared with experiment and other calculations.     

Metal-insulator transitions in Cr-doped V2O3 by x-ray and ultraviolet photoelectron spectroscopy

X-ray and ultraviolet photoelectron spectroscopy have been employed to investigate the high temperature metal-insulator transitions in V₂O₃ and (V_0.99Cr_0.01)₂O₃. The high temperature transitions are associated with more gradual changes in the 3d bands compared to the low-temperature transitions. Communication No. 20 from Solid State & Structural Chemistry Unit.     

Oscillator strengths and lifetimes calculated by the Dirac-Fock method for the levels of ions of the cesium isoelectronic sequence

A new method of data transmission in DWDM systems along existing long-distance fiber-optic communication lines is proposed. The existing method, e.g., uses 32 wavelengths in the NRZ code with an average power of 16 conventional units (16 units and 16 zeros on the average) and transmission of 32 bits/cycle. In the new method, one of 124 wavelengths with a duration of one cycle each (at any time instant, no more than 16 obligatory different wavelengths) and capacity of 4 bits with an average power of 15 conventional units and rate of 64 bits/cycle is transmitted at every instant of a 1/16 cycle. The cross modulation and double Rayleigh scattering are significantly decreased owing to uniform distribution of power over time at different wavelengths. The time redundancy (forward error correction (FEC)) is about 7% and allows one to achieve a coding enhancement of about 6 dB by detecting and removing deletions and errors simultaneously.     

The absorption spectrum of B II,C III,N IV and O V beryllium-like ions

Energy terms, dipole oscillator strenghts and photoionization cross sections from the ground state are calculated for beryllium-like ions. Autoionizing state transition energies and line widths for the ¹P⁰ resonances in the continuum are also obtained. The configuration interaction method for initial and final states is used, and the atomic orbitals are generated through angular- momentum-dependent, scaled Thomas-Fermi-Dirac potentials.     

Radiative strength functions for dipole transitions in 57, 59Co

Data on the (p, γ) reactions on ^{56, 58}Fe that were taken at proton energies of E _p =1.5–3.0 MeV and which were averaged over resonances are used to determine the absolute values of the radiative strength function at energies below 10 MeV. The results obtained in this way are compared with the results of the calculations that rely on the statistical approach and which take into account the temperature of the nucleus and its shell structure. Good agreement with experimental data is achieved without any variation of parameters.     

天体演化过程中CNO核子辐射俘获反应

C和N核的质子辐射俘获反应对恒星平稳H燃烧阶段的能量产生和元素核合成起重要作用, C, N和O 核的中子辐射俘获是原初核合成和AGB星核合成的关键反应, 精确测定它们天体物理反应率有重要意义。 除13N(p, γ)14O和16N(n, γ)17N等不稳定核的核子辐射俘获反应外, 国际上已完成了其中若干反应的直接测量工作。 但12C(p, γ)13N, 13C(p, γ)14N和15N(p, γ)16O等CNO循环关键反应的实验测量还没有达到天体物理感兴趣的能区。 13C(n, γ)14C,15N(n, γ)16N和18O(n, γ)19O等中子辐射俘获反应测量的能量跨度较大, 截面仍存在较大的不确定性。 介绍了这些反应的研究进展, 并讨论了间接测量这些反应的方法和可行性。 The proton radiative capture reactions of C and N nuclei are important for the energy production and nucleosynthesis in the CNO cycle, and the neutron radiative capture reactions of C, N and O nuclei are key reactions for the inhomogeneous Big Bang nucleosynthesis as well as for the neutron induced CNO cycle in AGB stars. So far, most of these reactions have been measured except some reactions of the unstable nuclei, such as 13N(p, γ)14O and 16N(n, γ)17N. While the direct measured reactions, such as the  12C(p, γ)13N, 13C(p, γ)14N and 15N(p, γ)16O key reactions in CNO cycle, have not reached down to the stellar energies. In addition, the large uncertainties still exist in the measured neutron capture reactions such as 13C(n, γ)14C,15N(n, γ)16N and 18O(n, γ)19O. Thus it is significant to determine their astrophysical reaction rates via the indirect measurements. In this paper, the research status and feasibility of the indirect measurements for these reactions are discussed.     

Radiative lifetimes of the NaRb C(3)1Σ+ state: experiment and theory

Radiative lifetimes for 2≤v^′≤44 rovibronic C¹Σ⁺ state levels of NaRb and quenching collision cross-sections with Rb atoms have been directly measured in a thermal cell by detecting time resolved laser induced fluorescence after pulsed excitation. Many body multipartitioning theory was applied to calculate C¹Σ⁺-X¹Σ⁺ and C¹Σ⁺-A¹Σ⁺ transition dipole moments. The relevant ab initio matrix elements were converted to the C¹Σ⁺ state radiative lifetimes. The strong spin-orbit A¹Σ⁺∼ b³Π coupling effect on the total C → A transition probabilities and lifetimes of the C¹Σ⁺ state is discussed. The measured radiative lifetimes show a decrease from 61 to 34 ns as the v^′ values increase, the results being in good agreement with calculations. The averaged collisional quenching cross-section value σ=(3±1)×10^-14 cm² was determined for NaRb (C¹Σ⁺) + Rb collisions from the Stern-Volmer plots.     

Radiative lifetimes,branching ratios and absolute transition probabilities of atomic uranium by delayed photoionization measurements

Radiative lifetimes of ten even-parity energy levels of atomic uranium in the 15,500–19,000 cm^?1 region and branching ratios of six transitions originating either from ground level (⁵L ₆ ^o ) or from lowest metastable level (⁵K ₅ ^o ) at 620.32 cm^?1 are measured employing three-step delayed photoionization technique. The lifetimes of five energy levels and branching ratios of five transitions are measured for the first time. By combining the experimentally measured values of radiative lifetimes and branching ratios, we have determined the absolute transition probabilities of six transitions of uranium and compared with those previously reported in the literature.     

Radiative transitions and the P wave levels in charmonium

A value of $\text{1}\text{2}$ or less for the ratio $\text{[E(2}{}^{\mathrm{++}}\text{) ? E(1}{}^{\mathrm{++}}\text{)]}\text{[E(1}{}^{\mathrm{++}}\text{) ? E(0}{}^{\mathrm{++}}\text{)]}$ of the P level splittings in approximate agreement with the assignment of the states at 3.41, 3.50 and 3.55 to the 0⁺⁺,and 2⁺⁺ P-wave levels, is obtained with a short-range Coulomb (Lorentz vector) potential together with a long-range linear (Lorentz scalar) confining potential. The radiative transition widths Γ(ψ′ → 3.41 + γ), Γ(ψ′ → 3.50 + γ), Γ(χ′ → 3.55 + γ) are significantly smaller than those obtained in previous (one-channel) charmonium calculations. The best results were obtained by allowing the Coulomb coupling constant α_s to have a momentum dependence suggested by asymptotic freedom formulae.     

L X-ray energy shifts and intensity ratios in tantalum with C and N ions — multiple vacancies in M, N and O shells

The energy shifts and intensity ratios of different L X-ray components in tantalum element due to 10 MeV carbon and 12 MeV nitrogen ions are estimated. From the observed energy shifts, the possible number of simultaneous vacancies in M shell are estimated. A comparison of L _α /L _β2.15, L _β1/L _γ1 and L _γ2.3/L _γ4.4 with the ratios due to Scofield theoretical transition rates indicate that the number of multiple vacancies in N shell are higher than the vacancies in M and O shell. Employing Larkin’s statistical scaling procedure, the number of possible multiple vacancies in N and O shells are estimated quantitatively.     

Stopping powers of C,N and O ions in Cr,Fe, Co,Ni, Cu and Zn in the 1 MeV region

The stopping powers of C, N, and O ions in Cr, Fe, Co, Ni, Cu and Zn in the energy range 500 keV to 2 MeV have been measured relative to that for He ions in the same material. The measurements were made utilizing energy spectra of particles backscattered from thick substrates of the target material into which a heavy material (Bi) had been previously implanted to a shallow depth. Assuming that dE/dx for He is known, the dose of implanted Bi can be determined from a He backscattering spectrum. Then this dose is used to calculate the unknown stopping power from a backscattering spectrum of the ion to be studied.

The data are analysed in terms of a function dE/dx=aE ^p +b The experimental results give values of p ranging from 0.3 to 0.5. Our absolute dE/dx values (normalized to known dE/dx values for He ions) are somewhat higher than those tabulated by Northcliffe and Schilling⁽³⁾ and considerably higher than predicted by the LSS⁽⁶⁾ theory.     

Radiative neutron capture by 2H, 7Li, 14C, and 14N nuclei at astrophysical energies

The possibility of describing experimental data on the total cross sections for the n ²H, n ⁷Li, n ¹⁴C, and n ¹⁴N radiative-capture processes within the potential cluster model involving forbidden states and their classification according to Young’s tableaux is considered. It is shown that this model and the methods used here to construct potentials make it possible to describe correctly the behavior of the experimental cross sections at energies between 5 to 10 meV (5 × 10^?3–10 × 10^?3 eV) and 1 to 15MeV.     

Tunable, high-repetition-rate, femtosecond pulse generation in the ultraviolet

We report efficient generation of tunable femtosecond pulses in the ultraviolet (UV) by intracavity doubling of a visible femtosecond optical parametric oscillator (OPO). The OPO, based on a 400 microm BiB3O6 crystal and pumped at 415 nm in the blue, can provide visible femtosecond signal pulses across 500-710 nm. Using a 500 microm crystal of beta-BaB2O4 internal to the OPO cavity, efficient frequency doubling of the signal pulses into the UV is achieved, providing tunable femtosecond pulses across 250-355 nm with up to 225 mW of average power at 76 MHz. Cross-correlation measurements result in UV pulses with durations down to 132 fs for 180 fs blue pump pulses.     

Excitation and neutron decay of xenon studied by forward-angle scattering of high-energy 17O ions

Excitation energy spectra and neutron decay of xenon have been measured in extreme forward angle scattering of 250A and 400A MeV ¹⁷O ions, using one quadrant of the CELSIUS storage ring as a magnetic spectrometer. The observed excitation energy spectrum, ranging from 12 to 36 MeV, has been compared with Coulomb cross section calculations. Neutron and missing energy spectra are compared with statistical decay calculations using the code CASCADE. In addition to statistical decay from giant resonances and other continuum excitations, a large fraction of forward peaked fast neutrons was observed throughout the entire excitation energy region. A possible reaction mechanism behind these fast neutrons is discussed.     

Heavy-ion reactions induced by O, O and F ions

Excitation curves have been determined from γ-ray yield measurements for heavyion reactions induced by E_lab = 12–30 MeV ¹⁶O, ¹⁸O and ¹⁹F ions incident upon thick targets of ⁹Be, ¹⁰B, ¹¹B, ¹²C and ²³Na. The yields of radioactive decay products with half-lives greater than one second were measured; hence a large number of the outgoing reaction channels could be observed. The preponderance of heavy reaction products suggests compound-nucleus formation as the dominant reaction mechanism. Statistical-model calculations with a spin-dependent level density have been performed, in which the nuclear moment of inertia was treated as a parameter. Many of the results can be explained satisfactorily with a nuclear moment of inertia 0.55 to 0.7 of the rigid body value.     

Radiative and Auger transitions of core-excited states for the boron isoelectronic sequence

We introduce an approach for the characterization of quantum correlations in two-fermion systems based upon the state disturbances generated by the measurement of “local” observables (that is, quantum observables represented by one-body operators). This approach leads to a concept of quantum correlations in systems of identical fermions different from entanglement.     

Micromirror SLM for femtosecond pulse shaping in the ultraviolet

We present the application of a novel micro mirror array, which is based on a micro electro mechanical system (MEMS), as one- and two-dimensional phase-modulating spatial light modulator (SLM) for femtosecond pulse shaping in the spectral region from the deep-ultraviolet (DUV) to the near-infrared (NIR) (200–900 nm). Using such a high-resolution MEMS-SLM, we demonstrate one-dimensional pulse shaping at 400 nm, including THz-pulse train generation, chirp compensation, and phase wraps. Received: 7 April 2003 / Published online: 2 June 2003 RID="*" ID="*"Corresponding author. Fax: +49-3461/947-202, E-mail: hacker@ioq.uni-jena.de