H. G. Berry

Measurement of the Stokes parameters of light

We describe a measuring system for determining the state of polarization of a beam of light in terms of its Stokes parameters. The technique which can be fully automated incorporates a monochromator and single photon counting detection and can thus be applied over a large wavelength range for very weak optical signals. Fourier transformation of the data by an on-line minicomputer allows immediate calculation of the Stokes parameters. We discuss special applications to light emitted from excited atomic systems with and without cylindrical symmetry.

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.

ANGULAR DISTRIBUTIONS OF IONS SCATTERED IN THIN CARBON FOILS.

Abstract The energy loss and scattering distributions of energetic light particles transmitted through thin carbon foils are determined. The dependence of the energy loss on the scattering angle is reported for 40 keV nitrogen ions in a carbon foil 5.7 μg/cm 2 thick. The angular halfwidths are reported for H, He, Li, N, Ne and Ar ions from 3 to 54 keV. A very simple empirical relation is established for the angular halfwidths of ions scattered in thin carbon foils in terms of their mean energy and atomic number and of the foil thickness. The experimental angular distributions and their halfwidths are compared with the new Meyer theory on plural and multiple scattering of ions in amorphous targets. The agreement is shown to be good.

Beam-foil spectroscopy

The measurement techniques of beam-foil spectroscopy are reviewed. These comprise the study of wavelengths of heavy ions with low and high charge states at visible, UV and X-ray wavelengths from normal excited states, multiply excited states and high-n Rydberg levels; the measurements of mean lifetimes above 10-12 s and metastable states up to 100 ns; high-resolution Auger electron measurements; and the application of atomic alignment and orientation by both perpendicular and tilted foils to measurements of atomic structures and analysis of the beam-foil excitation process. A theoretical description of the emission of light from anisotropically excited systems is included. Associated techniques of time-resolved spectroscopy are compared.

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.

Beam-Foil Spectrum of Sulfur 600–4000 Å

The beam-foil spectrum of sulfur in the wavelength region 600–4000 A has been measured for a series of beam-particle energies from 0.5 to 2.0 MeV. Transitions in S I–S vI have been identified. In addition, many strong unidentified sulfur lines were observed and approximate charge states have been suggested by the variation of intensity of these lines with incident-particle energy. Mean lives of 46 of the stronger transitions were measured. Twenty-seven of these correspond to transitions between known levels of S II–S vI.

Mean Lives of Excited Levels in O i–O vi*

Oxygen spectra between 450 and 2200 A were studied with the beam-foil technique. Mean lives of over 50 excited levels in O i–O vi were measured.

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.

Multiply-excited States in Beam-foil Spectroscopy

The phenomenon of the excitation of multiply-excited states in beam-foil spectroscopy is reviewed: 1. Introduction, early B.F.S. work. 2. (a) Earlier non-beam-foil observations of multiply-excited states; (b) Theoretical development of multiply-excited systems; (c) Experiments and theory since 1961. 3. B.F.S. photon measurements: (a) He I isoelectronic sequence. (b) Li I isoelectronic sequence. (c) Be I and heavier isoelectronic sequences. (d) Transition probabilities, comparison of theory and experiment. 4. B.F.S. electron measurements. 5. The beam-foil interaction process. 6. Present problems and future aspects.

Energies and Mean Lives of Doubly Excited Terms in Lithium

We have observed approximately 50 new lines in the spectrum of a beam of foil-excited lithium ions (0.5–1.0-MeV beam energy) in the wavelength region 2000–11 000 A. One line is classified as a transition in doubly excited Li ii, and the remainder are attributed to transitions between highly excited levels in Li ii, and to transitions in the doubly excited quartet and doublet systems of Li i. Six lines remain unidentified. Mean lives have been measured for some of the new Li i transitions. They help to verify the suggested identifications.