Lars Åke Svensson

Production of Silica Aerogel

A production facility for silica aerogel has been set up in Lund. Aerogel is now produced in large quantities with the refractive indices of 1.03 and 1.05. The standard block size is 18 × 18 × 3 cm3.

An Experimental Study of 3s23pk and 3s3pk+1 in the CI I, S I, P I, Si I, and AI I Isoelectronic Sequences

New measurements and identifications of the transitions 3s23pk-3s3pk+1 have been made in the spectra of S IV, K IV-VII, Ca V-VIII, Sc VI-IX, Ti VII-X, V VII-XI, Cr VIII-XI, Mn IX-XI, and Fe X, XI. The energy parameters of the ground configurations have been determined and expressed as functions of Z by semi-empirical formulae in the S I, P I, Si I, and Al I isoelectronic sequences. Predicted wavelengths for some 150 forbidden lines of astrophysical interest are tabulated.

Analyses of the XUV Spectra of K, Ca, Sc and Ti Isoelectronic with P I, Si I and Al I

An isoelectronic comparison of spectra in the P I, Si I and Al I sequences has been made for the elements K, Ca, Sc and Ti. In the course of this study we have also identified some lines in the spectra of adjacent elements in the same sequences, for example S IV, Ar IV, Ar V and Ar VI. In the P I and Si I sequences the study is restricted to transitions to the ground configurations 3s23p2 and 3s23p3. In the Al I like spectra we have identified transitions between the configurations 3s23p, 3s3p2, 3p3, 3s2nd, 3s2nf, 3s3p3d and 3s3p4s, where the nd and nf series have been traced to n = 6, and for nf in Ca VIII to n = 7.

The identification of Feix and Nixi in the solar corona

The levels of the configuration 3s23p53d of Fe ix have been experimentally determined from their combinations with 3s3p63d3D in the region 300–400 Å. Wavelengths can now be accurately predicted for all transitions within 3s23p53d, and eight of these can be identified with coronal lines from 2042 to 4585 Å. Also, identifications of solar lines from 171 to 245 Å with electric-dipole and magnetic-quadrupole transitions to the ground state, 3s23p61S, are confirmed and extended. Solar identifications with corresponding transitions in Ni xi, both within 3s23p53d and to the ground state, are proposed on the basis of a short extrapolation.

An Aerogel Cerenkov Counter for the AFS Experiment

A large aerogel Cerenkov counter has been constructed for the open axial field magnets at the CERN ISR. Due to the detector position in a strong magnetic field, and limited space, an unconventional readout method has been employed using wave length shifter.

Predicted wavelengths of coronal transitions in the configurations 3s23p2, 3s23p3 and 3s23p4

The level intervals in the ground configurations 3s23pk(k = 2, 3, 4) have been studied through the isoelectronic sequences up to Ni. Semiempirical expressions for the parameters F2(pp) and ζp, are derived from observed data and the intervals are recalculated from interpolated or extrapolated values of the parameters. As a result, predicted wavelengths of magnetic-dipole transitions within the configurations are obtained with an estimated uncertainty of one or two Å.

The Spectrum of Four-Times-Ionized Titanium, TiV

By means of a 3-m normal-incidence spectrograph the following transitions of Ti V have been observed: 3d-4p (66 lines in the region 440-580 A), 4s-4p (27 lines, 1 250-2 400 A), 4p-5s (19 lines, 800-1 000 A), 4p-4d (52 lines, 1 000-1 500 A). In addition, the configuration 3s3p63d, which is highly mixed with 4p, has been determined by 64 combinations with 3d, 4s, 4d and 5s. Energy parameters are derived from least-squares fits of observed levels and compared to Hartree-Fock calculations. By an isoelectronic extrapolation the ionization energy is found to be 800 550 ± 200 cm-1.

Spectrum and Term System of Ti XII

The spectrum of eleven times ionized titanium has been observed by using a condensed vacuum-spark discharge and a 5-m grazing-incidence spectrograph and a 3-m normal-incidence spectrograph. Fortythree lines have been identified in the region 52-960 A. The ns- and np-series have been extended to n = 6 and the nd- and nf-series to n = 8. The derived ionization energy of Ti XII is 2 351 100±60 cm-1 (291.49 eV).

The Configurations 3s23p53d and 3s3p63d in Mn VIII and Fe IX

The astrophysically important configuration 3s23p53d has been determined for Mn VIII and Fe IX by means of about 60 lines, classified as combinations 3s23p6-3s23p5 3d and 3s23p53d-3s3p63d. We also introduce a sensitive method for isoelectronic comparison of energy parameters. By this method the configuration 3s23p53d is studied through the Ar I sequence, thus supporting the reported Mn VIII and Fe IX identifications.

The Transitions 3s23pk-3s3pk+1 of Ti VI and Ti VII

The transitions 3s23pk-3s3pk+1 have been measured in Ti VI (k = 5) and Ti VII (k = 4). In Ti VI the observed ground-term interval is found to be 5 829.3±1.1 cm-1. A four-parameter formula, expressing the Z-dependence of this interval, has been derived from the best observed values through the sequence from Cl I to Ni XII. It reproduces the observed intervals within their error limits. In Ti VII the ground-configuration intervals are measured and compared to previous measurements and calculations.