535 research outputs found
Laboratory simulation of cometary x rays using a high-resolution microcalorimeter
X-ray emission following charge exchange has been studied on the University
of California Lawrence Livermore National Laboratory electron beam ion traps
EBIT-I and EBIT-II using a high-resolution microcalorimeter. The measured
spectra include the K-shell emission from hydrogenlike and heliumlike C, N, O,
and Ne needed for simulations of cometary x-ray emission. A comparison of the
spectra produced in the interaction of O8+ with N2 and CH4 is presented that
illustrates the dependence of the observed spectrum on the interaction gas.Comment: 11 pages, 2 figure
Multipole (E1, M1, E2, M2, E3, M3) transition wavelengths and rates between 3l5l' excited and ground states in nickel-like ions
A relativistic many-body method is developed to calculate energy and
transition rates for multipole transitions in many-electron ions. This method
is based on relativistic many-body perturbation theory (RMBPT), agrees with
MCDF calculations in lowest-order, includes all second-order correlation
corrections and includes corrections from negative energy states. Reduced
matrix elements, oscillator strengths, and transition rates are calculated for
electric-multipole (dipole (E1), quadrupole (E2), and octupole (E3)) and
magnetic-multipole (dipole (M1), quadrupole (M2), and octupole (M3))
transitions between 3l5l' excited and ground states in Ni-like ions with
nuclear charges ranging from Z = 30 to 100. The calculations start from a
1s22s22p63s23p63d10} Dirac-Fock potential. First-order perturbation theory is
used to obtain intermediate-coupling coefficients, and second-order RMBPT is
used to determine the matrix elements. A detailed discussion of the various
contributions to the dipole matrix elements and energy levels is given for
nickellike tungsten (Z = 74). The contributions from negative-energy states are
included in the second-order E1, M1, E2 M2, E3, and M3 matrix elements. The
resulting transition energies and transition rates are compared with
experimental values and with results from other recent calculations. These
atomic data are important in modeling of M-shell radiation spectra of heavy
ions generated in electron beam ion trap experiments and in M-shell diagnostics
of plasmas.Comment: 21 pages, 8 figures, 11 table
Critical Test of Simulations of Charge-Exchange-Induced X-Ray Emission in the Solar System
Experimental and theoretical state-selective X-ray spectra resulting from
single-electron capture in charge exchange (CX) collisions of Ne^10+ with He,
Ne, and Ar are presented for a collision velocity of 933 km s^-1 (4.54 keV
nucleon^-1), comparable to the highest velocity components of the fast solar
wind. The experimental spectra were obtained by detecting scattered
projectiles, target recoil ions, and X-rays in coincidence; with simultaneous
determination of the recoil ion momenta. Use and interpretation of these
spectra are free from the complications of non-coincident total X-ray
measurements that do not differentiate between the primary reaction channels.
The spectra offer the opportunity to test critically the ability of CX theories
to describe such interactions at the quantum orbital angular momentum level of
the final projectile ion. To this end, new classical trajectory Monte Carlo
calculations are compared here with the measurements. The current work
demonstrates that modeling of cometary, heliospheric, planetary, and laboratory
X-ray emission based on approximate state-selective CX models may result in
erroneous conclusions and deductions of relevant parameters.Comment: 4 figure
The X-ray spectrum of Fe XVII revisited with a multi-ion model
The theoretical intensities of the soft X-ray Fe XVII lines arising from
2l-3l' transitions are reexamined using a three-ion collisional-radiative model
that includes the contributions to line formation of radiative recombination
(RR), dielectronic recombination (DR), resonant excitation (RE), and
inner-shell collisional ionization (CI), in addition to the usual contribution
of collisional excitation (CE). These additional processes enhance mostly the
2p-3s lines and not the 2p-3d lines. Under coronal equilibrium conditions, in
the electron temperature range of 400 to 600 eV where the Fe XVII line
emissivities peak, the combined effect of the additional processes is to
enhance the 2p-3s lines at 16.78, 17.05, and 17.10 A, by ~ 25%, 30%, and 55%,
respectively, compared with their traditional, single-ion CE values. The weak
2p-3d line at 15.45 A is also enhanced by up to 20%, while the other 2p-3d
lines are almost unaffected. The effects of DR and RE are found to be dominant
in this temperature range (400 - 600 eV), while that of CI is 3% at the most,
and the contribution of RR is less than 1%. At lower temperatures, where the Fe
XVII / Fe XVIII abundance ratio is high, the RE effect dominates. However, as
the temperature rises and the Fe XVIII abundance increases, the DR effect takes
over.
The newly calculated line powers can reproduce most of the often observed
high values of the (I17.05 + I17.10) / I15.01 intensity ratio. The importance
of ionization and recombination processes to the line strengths also helps to
explain why laboratory measurements in which CE is essentially the sole
mechanism agree well with single-ion calculations, but do not reproduce the
astrophysically observed ratios.Comment: Submitted to Ap
Non-thermal processes in coronae and beyond
This contribution summarizes the splinter session "Non-thermal processes in
coronae and beyond" held at the Cool Stars 17 workshop in Barcelona in 2012. It
covers new developments in high energy non-thermal effects in the Earth's
exosphere, solar and stellar flares, the diffuse emission in star forming
regions and reviews the state and the challenges of the underlying atomic
databases.Comment: To appear in the proceedings of the Cool Stars 17 worksho
Nuclear-polarization effect to the hyperfine structure in heavy multicharged ions
We have investigated the correction to the hyperfine structure of heavy
multicharged ions, which is connected with the nuclear-polarization effect
caused by the unpaired bound electron. Numerical calculations are performed for
hydrogenlike ions taking into account the dominant collective nuclear
excitations. The correction defines the ultimate limit of precision in accurate
theoretical predictions of the hyperfine-structure splittings
Solubility and Cation Exchange Properties of Synthetic Hydroxyapatite and Clinoptilolite Mixtures
A zeoponic plant growth system is defined as the cultivation of plants in artificial soils, which have zeolites as a major component. These systems: 1) can serve as a controllable and renewable fertilization system to provide plant growth nutrients; 2) can mitigate the adverse effects of contamination due to leaching of highly soluble and concentrated fertilizers; and 3) are being considered as substrates for plant growth in regenerative life-support systems for long-duration space missions. Batch-equilibrium studies of the dissolution and ion-exchange properties of mixtures of naturally-occurring Wyoming clinoptilolite (a zeolite) exchanged with K(+) or NH4(+); and synthetic hydroxyapatite were conducted to determine: 1) the plant availability of the macro-nutrients NH4-N, P, K, Ca, and Mg and 2) the effects of varying the clinoptilolite to hydroxyapatite ratio and the ratio of exchangeable cations (K(+) vs. NH4(+)) on clinoptilolite extraframework sites. The nutrients NH4-N (19.7 to 73.6 mg L(sup -1), P (0.57 to 14.99 mg L(sup- 1), K (14.8 to 104.9 mg L(sup -1), and Mg (0.11 to 6.68mg L(sup -1) are available to plants at sufficient levels. Solution Ca concentrations (0.47 to 3.40 mg L(sup -1) are less than optimal. Solution concentrations of NH4(+), K(+), Ca(2+), and Mg(2+) all decreased with increasing clinoptilolite to hydroxyapatite ratio in the sample. Solution concentrations of phosphorous initially increased, reached a maximum value and then decreased with increasing clinoptilolite to hydroxyapatite ratio in the sample. The NH4(+) -exchanged clinoptilolite is more efficient in dissolving synthetic hydroxyapatite than the K(+) -exchanged clinoptilolite. This suggests that NH4(+), which is less selective at clinoptilolite extraframework sites than K(+) is exchanged more readily by Ca(2+) and thereby enhances the dissolution of the synthetic hydroxyapatite
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