Table of contents

Nuclear particle detectors have been made by ion-implantation. Energy resolution of 22 kev has been obtained.

The energy of the (h_9/2)₈₊² isomeric state in ²¹⁰Po has been determined from studies of the ²⁰⁸Pb(α, 2n)²¹⁰Po reaction. The value 1556.9 keV was deduced from the known energy of the 6⁺ level and the observed 8⁺ → 6⁺ 83.7 keV transition. For the h_9/2 proton orbit we obtained e_eff/e = 1.52 ± 0.06 by comparing the experimental and theoretical B(E2) values.

The energies and intensities of gamma radiation from thermal neutron capture in an enriched sample of ¹⁸⁰Hf have been determined by means of a Ge(Li) pair and anti-Compton spectrometer. An internal reactor target has been used. The reaction Q-value, the energies of the excited states and the decay scheme of ¹⁸¹Hf have been deduced. A large number of low K-value states are found in the range of excitation energy from 1 to 2 MeV.

Halflives of some excited states in decay products of ThB (²¹²Pb) have been measured by the delayed coincidence technique. For ²⁰⁸Pb the results are: 3 198 keV level 286±26 ps, 3 475 keV level 4±3 ps, 3 961 keV level ⩽ 18 ps. For ²¹²Bi the results are: 238 keV level ⩽ 5 ps, 415 keV level ⩽ 10 ps, 115 keV level (8±4) ps. The use of ThB, ⁶⁰Co and ¹⁹⁸Au as time calibration standards is discussed.

Measurements were made on the time distributions of the prompt gamma radiation emitted from fragments in the thermal-neutron induced fission of ²³⁵U. The gamma radiation emitted during different time intervals after the fission event was studied with the help of a collimator, the position of which was changed along the path of the fragments. In this way decay curves were obtained from which half-lives could be estimated. Time components with half-lives of 7.5, 18 and 60 ps were found and their relative intensities were calculated. Half-lives and associated intensities are in good agreement with earlier data from uranium and californium fission. Problems involved in this type of study are discussed. The collimator technique has proved to be effective for determination of half-lives down to less than 10 ps.

Transitions in the decay of ¹⁶⁸Tm to ¹⁶⁸Er have been studied by measurements of electron-gamma directional correlations. The M1-contributions of the 632-, 731- and 816-keV transitions between the gamma-vibrational band and the ground state rotational band have been determined to amount to less than 0.8%. The 99-, 198- and 830-keV transitions depopulating the 1094-keV state have been determined to be of predominantly E1-character. A pure E1-multipolarity for the 99-keV transition is however possible only if a penetration effect is present in the internal conversion process characterized by a nuclear current parameter

η = 303_-8⁺⁷ or η = -12.2_-2.0^+2.0

We have measured radiative decay times in Si II, Si III, and Si IV in the wavelength region 700-6 000 Å 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.

The spectrum of singly ionized neon emitted by a hollow-cathode discharge has been observed in the 11 000-300 Å range. Wavelengths have been determined for 1 250 Ne II lines of which about 950 are new. The extended wavelength observations have led to the finding of more than 220 new energy levels, which means that in all 301 Ne II levels, belonging to the configurations 2s²2p⁵, 2s2p⁶, 2s²2p⁴3s-7s, 3p-5p, 3d-5d, 4f-9f, and 5g-7g are now known. The derived term system has been fixed in relation to the ground term using improved values for the wavelengths of the resonance lines 2s²2p⁵²P_1½,½-2s2p⁶²S_½ at 460.7284 and 462.3908 Å. The ³P₂ ionization limit has been determined to be (330 388.6±0.3) cm^-1 above the ground level. Accurate wavelengths, useful as reference wavelengths, have been calculated in the 2 000-1 000 Å and 460-300 Å regions.

The spectrum of doubly ionized calcium, Ca III, has been investigated between 2 290 and 9 640 Å, and 222 lines have been measured, of which 143 were not known before. Between 9 640 and 12 000 Å no Ca III line was observed. As a result of the analysis all levels belonging to 3p⁵6s, 5p, 5d, 6g, and 7g (two levels masked) are now known in addition to those reported in a previous paper (3p⁵4s, 5s, 4p, 3d, 4d, 4f, 5f, 5g, and parts of 6d, 6f and 7f). In the vacuum ultraviolet, 50 more lines have been classified. The coupling of all configurations has been studied; the 3p⁵ng configurations show pronounced JK coupling. The ²P_1½ and ²P_½ limits derived from ng series with high J values are 410 642.3±2 and 413 760.2±2 cm^-1 respectively.

Electron impact ionization cross sections are calculated for Be (Z=4) up to Thorium (Z=90) for single ionization of inner subshells with binding energies of 100 eV to 1 000 eV. The simple formula used for calculating these cross sections is tested by comparing with experimental results available in a region of low energy incident electrons. A modified formula is shown to be a rather good approximation also for relativistic energy levels.

The resistances of thin gold films have been measured and monitored during condensation on substrates of SiO and glass. It has been shown that the different growth stages of thin films can be easily determined from the plotted curves of resistance vs. incoming atoms, while the structural properties, e.g. island density and gap widths, have turned out to be very sensitive to substrate conditions. It has also been shown that thermionic emission seems to be the main conduction mechanism. This suggestion has been based on comparisons between an extended theory and the experiments performed.

Combined magnetic and electric interaction is studied for cadmium in ferromagnetic gadolinium. The magnetic hyperfine field at 15 K is determined to be - 327(8) kG and its temperature dependence is compared to the magnetization at nearest Gd atoms. The angle β which the magnetic hyperfine field forms with the main component of the electric field gradient tensor is found to vary smoothly with temperature from β ≈ 35° at 0 K to β = 0° at the Curie temperature (293 K).

The reduced magnetic hyperfine field B_hf(T)/B_hf (4.2) for Gd in Gd metal has been studied. A deviation from the magnetization curve ((σ(T)/σ(0)) is found and is discussed in terms of the d-character of the conduction electrons and possible orbital contributions introduced by spin-orbit coupling.

An effective field model for magnetic moments in exchange-enhanced metals and alloys is developed. It is shown how a simple diagrammatic method can be used to generalize the model. The results are interpreted in exchange scattering and interaction processes between electrons in resonant bound and band states. The d-electrons are considered mostly localized. Very good agreement with data on 1 at-% Mn in Pd is found. It is argued that the exchange interaction constant may always be negative. Positive interaction constants corresponding to parallel spins for the lowest energy state are explained by indirect exchange interaction between magnetic moments and scattering of conduction electrons.

Measurements on the dispersion of the refractive index n of AlP and AlAs are related to recent developments in dielectric theory. The values for the dispersion parameters found in these compounds agree with those expected from comparison with other zinc-blende compounds, and the measured absolute values of n are in good agreement with theoretical estimates. The ionic character of AlP and AlAs was found to be larger than for GaP and GaAs, contrary to previous conclusions.