Lorenzo J. Curtis

A meanlife measurement of the 3d2D resonance doublet in SiII by a technique which exactly accounts for cascading

Abstract The meanlife of the 3d 2 D doublet in SiII has been determined to be 0.47 ± 0.03 ns by a technique which utilizes arbitrarily normalized decay curves of all direct cascades in the analysis of the decay curve of the measured level, and thus exactly accounts for cascade effects.

Lifetime Measurements in Si II, Si III, and Si IV

We have measured radiative decay times in Si II, Si III, and Si IV in the wavelength region 700-6 000 ? using the beam-foil technique. The lifetimes and transition probabilities have been evaluated by alternative methods of curve-fitting and cascade analysis. These results are compared with theoretical transition probabilities, and values in other members of the isoelectronic sequences. A recently introduced cascade analysis technique is shown to extract reliable lifetimes from heavily cascaded decay curves which are unresolvable by normal curve-fitting techniques. It can also yield information on the relative populations of the excited levels produced in the foil interaction. The present estimates of silicon in astrophysical objects are not changed by our measurements of transition probabilities in Si II and Si III. The solar photospheric and coronal abundance estimates of silicon relative to hydrogen thus still differ by a factor of three. We have measured the transition probabilities of most of the silicon lines observed in the red-shifted quasar spectra.

Distortion effects in measurements of long optical lifetimes

An extensive review is given of various effects that might distort decay curves of long-lived atomic and molecular states in measurements using a static gas target. Special emphasis is given to effects due to the escape out of the viewing region due to thermal motion and, in the case of ions, due to electrostatic repulsion. Theoretical models and experimental measurements are presented which indicate that, for a known geometry, an experimental decay curve can be corrected for the thermal losses so that lifetimes even as long as 1 ms can be deduced if copious excitation is achieved. Studies of the electrostatic repulsion losses show that this effect is strongly dependent upon the density of secondary electrons present and it can easily be eliminated by a supply of additional low-energy electrons. Thus this work shows that it is feasible to utilize the great advantages of static gas multichannel techniques and perform reliable high-resolution recording of lifetimes even in the > 1 μs range.

Analysis of Multi-exponential Decay Curves

The contributions of cascades to multi-exponential decay curves are analysed. We define the quantitative cascade contribution to an exponential decay as the replenishment ratio, which is the ratio of the cascade repopulation rate to the decay depopulation rate. We recommend that this ratio be quoted in future papers on beam-foil or other cascade-affected decay measurements. We also present specific relationships between the fitting parameters and the level populations for decay curves which arise from electric dipole transition schemes of up to second order in cascading. Velocity dispersion effects in beam-foil decays are, in general, shown to be negligible, except for decays from ejected foil-particles.

Lifetimes of Excited Levels in PI-PV

We have studied the beam-foil spectra of phosphorus between 600 and 2 200 A and measured radiative lifetimes for 21 excited terms in P I-P V. We discuss the merits of several methods for evaluating the decay constants and compare the results with theoretical transition probabilities as well as with recent experimental studies of oscillator strengths in the P I, Si I, Al I, Mg I, and Na I isoelectronic sequences.

Use of the Einstein–Brillouin–Keller action quantization

The Einstein–Brillouin–Keller semiclassical quantization and the topological Maslov index are used to deduce the correct quantum mechanical values for the energy of a one-electron atom (both nonrelativistically and relativistically) and a three-dimensional harmonic oscillator. The development is concise, transparent, and involves only elementary integral calculus and provides a conceptual and intuitive introduction to the quantum nature of the atomic and molecular structure of matter.

Semi-Empirical Oscillator Strengths for the Cu I Isoelectronic Sequence

Semi-empirical values for the lifetimes, transition probabilities and oscillator strengths have been computed for all n = 4, n = 5 and some n ≤ 9 Rydberg transitions for ions in the Cu I isoelectronic sequence through In XXI. Extrapolation and interpolation techniques were utilised to obtain a set of estimated term values and ionisation potentials which, although crude by spectroscopic standards, are of sufficient accuracy to serve as inputs for transition probability calculations by the numerical Coulomb approximation.

A Diagrammatic Mnemonic for Calculation of Cascading Level Populations

A diagrammatic procedure is described, by which the time dependence of the population of any level in a decay scheme of arbitrary complexity can be prescribed directly in terms of transition probabilities and initial populations, without specifically solving the determining differential equations.

Isoelectronic wavelength predictions for magnetic-dipole, electric-quadrupole, and intercombination transitions in the Mg sequence

Precise wavelength predictions are presented for the 3s3p3P1–3s3p3P2 magnetic-dipole transitions, the 3s3p3P0–3s3p3P2 electric-quadrupole transitions, and the 3s2 1S0–3s3p3P1 intercombination lines for all members of the Mg isoelectronic sequence with Z ≤ 45. Magnetic-dipole and intercombination transitions of this type have recently been observed in tokamak spectra and have applications for localized diagnostics in high-temperature plasmas. The predictions are based on interpolations and extrapolations of empirical regularities, which also provide insights into the dynamics of these atomic systems.

New cascade analysis techniques for determining spontaneous atomic transition probabilities

Abstract Several new analysis techniques which account for the effects of cascades in the measurement of atomic transition probabilities have been developed at the University of Toledo, and will be described here. These techniques involve the incorporation of information from the direct measurement of the decay curves of cascading transitions into the analysis of the decay curve of the main level of interest. The traditional curve fitting techniques, as well as the new analysis techniques, are investigated by the use of computer simulated data containing various numbers of known exponentials. A diagrammatic mnemonic which trivially generates the theoretical decay curves for cascade schemes of arbitrary complexity will be described. The traditional curve fitting techniques are extended to include constraints imposed by the coefficients in the theoretical decay curve, which can be measured in terms of relative intensities of the cascading transitions. The population differential equation is converted to an integral equation involving only experimentally measurable quantities and the desired transition probability. Integrals over some arbitrary time interval of the decay curves can be photometrically measured, and given a common normalization through a wavelength relative efficiency calibration of the detection system. Integrated decay curves of all transitions, either directly into or out of the level of interest, can be summed in a manner which determines its transition probability. By varying the choice of time interval it can be verified that all contributing transitions have been correctly included. A variation of this technique allows the construction of the decay curve of an unmeasured cascade, provided the transition probability of the level into which it cascades is known. This variation can be used to investigate radiationless transitions and transitions outside the range of available detectors. Further, if there is additional a priori information concerning the shape of the unseen cascade decay curve, both its litetime and that level into which it cascades can be determined.