Table of contents

Some exact solutions are obtained for energy dependent slowing down problems with energy dependent cross sections. The transport equation is solved using the backward-forward model of Fermi. Also studied is the energy dependent diffusion equation. Using these models, and a novel technique involving difference equations, it has been possible to find explicit, and numerically useful, solutions for slowing down from a plane, monoenergetic source in an infinite medium. The slowing down density and the energy deposition function are obtained which are of value in reactor physics and radiation damage calculations.

Single-particle properties for Λ and K_s⁰ from 2V⁰ events have been compared with corresponding properties of inclusively produced Λ and K_s⁰. By comparison of the inclusive production of Λ with the properties of Λ observed together with K_s⁰ we have separated the reactions pp → ΛK⁺[+]X⁺ and pp → ΛK⁰ + X⁺⁺. We show that these reactions are significantly different, the former reaction producing a more "peripheral" Λ than the latter. A comparison with a peripheral phase space model shows that the K_s⁰K_s⁰ and ΛK_s⁰ events are well described by this model when the "average" final states are taken to be NNK4π and ΛNK4π, respectively.

The angular and rapidity distributions of secondary charged particles from p-N interactions at 400 GeV/c for charged particle multiplicity ⩾ 4 are presented. The forward-backward ratio in the centre of mass system is found to be 1.54 ± 0.07. The rapidity distribution shows a plateau in the central region with a mean value 3.81 ± 0.03. The study of rapidity dispersion indicates that in ∼ 30% of the events single nova is produced.

Activation cross-sections for neutron capture have been measured at an energy of 14.7 ± 0.3 MeV for the nuclei ²³Na, ⁵⁵Mn, ⁸⁹Y, ¹²⁷I, ¹³⁸Ba, ¹⁸⁶W and ¹⁹⁷Au. The influence of secondary neutrons was studied both experimentally and theoretically. The corrections due to secondary low-energy neutrons were determined by systematically varying the geometrical parameters.

Previous beam-foil lifetime studies in the EUV range are extended to cover all n = 2 states of Si VII and Si IX. The lifetime values obtained agree with theoretical data of Nicolaïdes and Beck. For some states of Si X and Si XI information about initial population ratios of singly and doubly excited states is obtained. After foil excitation, the contribution of cascades from doubly excited states in the n = 2 shell to the intensities of decays from singly excited to ground states amounts to 20-40%.

Foil excitation of ³¹P ions at 19 MeV has been used to produce singly and doubly excited states of highly ionized phosphorus atoms. The EUV spectrum in the wavelength range 10 nm < λ < 55 nm has been observed and analyzed by means of a 2.2 m grazing incidence monochromator. General agreement with tabulations based on observations with other light sources has been found. Decay curves of 22 n = 2, Δn = 0 transitions in P IX-P XII have been taken. The evaluation procedure accounts for the spatial resolution function. As in the case of silicon, the decays of singly excited states appear to be strongly fed by cascades from doubly excited states in the n = 2 shell. The lifetime results are in general agreement with theoretical predictions.

A survey of recent analyses of Sc II, Ti II and Fe II and of other spectra of the singly-ionized iron-group elements demonstrates that the "horizontal" regularities first described by Catalán are valid for several kinds of excited configurations. From systematic parametric studies it is shown that the radial parameters have a smooth dependence on k for 3d^k-14s4p, 3d^k4d and 3d^k4f configurations. From these results the position and level structure of unknown configurations can be predicted.

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.

We have measured Auger electrons emitted from atomic (C⁺-, N⁺-, O⁺)- and molecular (N₂⁺-, CO⁺)-projectiles (ca. 80 keV A^-1) excited under single collision conditions in thin gaseous targets (N₂, CO₂). The dominant lines in the observed spectra can be attributed to the decay of Li-and Be-like configurations using intermediate coupling Dirac-Fock calculations. Molecular projectiles (N₂⁺ and CO⁺) loose their binding electrons in the collisions and the molecular fragments explode via Coulomb repulsion, imposing their kinematics on the deexcitation radiation. This results in an additional kinematic line broadening in the Auger electron energy spectra. It can be well separated from all other contributions to the total linewidth by comparing the spectra of atomic and molecular projectiles of equivalent velocity.

In the spectral range between 4100 and 6800 Å the Stark effect shift and splitting of 91 lines of neutral argon was studied, using electric field strengths of up to 700 kV cm^-1. The investigations show that the behaviour of the lines can be interpreted as a shift and splitting of the upper levels of the lines. For these levels the results are given in the form of coefficients which enable the calculation of the Stark shifts.

The silicon KL_{2, 3}L_{2, 3}(¹D₂) Auger energies and the silicon 2p_3/2 binding energies have been measured for more than twenty organic silicon compounds in the gas phase. The group shift model has been applied to the Auger energy data as well as the binding energy data. Approximate proportionality between these two types of chemical shifts was found for some sub-series of the type SiR_4-nT_n. The transition potential model for the transition from one to two holes in the silicon core has been developed to take into account the difference between the 1s and 2p binding energy shifts. Semi-empirical calculations have been performed for most of the compounds, CNDO/2 and EWMO (a modified iterative extended Hückel method, briefly presented in the text). It was found that EWMO provides a more satisfactory description of the valence charge densities and their changes upon core ionization than does CNDO/2. The correlation with the experimental data was also found to be better applying the transition potential models to the EWMO calculated charges than to the CNDO/2 charges.

The L-shell soft-X-ray emission spectra of Cu, Zn, Ga, As, Br, Rb and Sr from laser-produced plasma sources were recorded with a convex-crystal spectrograph. The spectrograms were measured to provide wavelengths accurate to ± 2 mÅ for neon-like and 2p⁵-2p⁴3s, 3d fluorine-like transitions. Theoretical wavelengths and oscillator strengths were computed to aid the classification of the experimental spectra.

Ionisation potentials are derived for the neon-like ions of Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, and Y by applying the Ritz law to observed wavelengths in one or both of the 2p⁶¹S_o-2p⁵nd¹P₁, ³D₁ Rydberg series. The wavelengths are adjusted to allow for mutual and configuration interaction. The potential of neon-like Ar IX is determined from energy levels in the 2p⁵nd³F₄ series. The derived potentials systematically exceed the predictions of Edlén's (1971) non-relativistic semi-empirical formula. The differences are much larger than experimental uncertainties and are interpreted as a relativistic contribution to the ionisation potential. The Edlén formula is amended to allow for the newly derived potentials and to include theoretical calculations of the relativistic contribution by Snyder. The revised formula reproduces the potentials for Si V and higher ions to within experimental uncertainty. Discrepancies for Ne I to Al IV may be due to the correlation energy.

Previous stability calculations concerning current and magnetic curvature driven electrostatic modes in a cold plasma mantle are generalized. In particular the commonly used adiabatic approximation is relaxed and replaced by an energy balance. In the theory presented important new effects associated with heat conduction, ionization and ohmic heating are found. In combination with viscosity and resistivity these effects introduce additional stabilizing as well as destabilizing effects. The present theory predicts stability properties similar to the adiabatic one in the limit d(ln T)/d(ln n) ≪ 1, but shows less favourable stability properties in the limit d(ln T)/d(ln n) ≫ 1. One may speculate that these conclusions also apply to more general types of electrostatic modes associated with density and temperature gradients in cold plasma mantle boundary layers.

A generation of a d.c. electric field at ferromagnetic resonance or the magnetoelectric effect in magnetic semiconductors is studied theoretically in the whole magnon wave vector space. The magnetoelectric effect in the classical regime kl < 1 and contributions of different electron-magnon interactions to the magnon drag effect in the quantum regime kl > 1 are calculated. All the calculated static electric fields are compared with experimental results. At low-microwave power levels the non-linear electrodynamic interaction due to a mixing of the oscillating magnetization (k = 0) and the induced electric field seems to dominate the magnetoelectric effect. In some cases the classical drag effect may also be significant. At sufficiently high power levels the quantum mechanical magnon drag can make the largest contribution. It is shown that in the magnon drag effect the induced static electric field is proportional to the damping coefficient of magnons.

It has been proposed to sound the ionosphere by means of nonlinear mixing of two VHF/UHF waves of different frequency. This paper studies the problem theoretically, including the earth's magnetic field, collisions and plasma inhomogeneity. We find that collisions, and sideways drift of wave packets due to perpendicular components of the group velocity, may seriously affect the results when the plasma inhomogeneity is weak. Also, the effect is favoured if the pump waves have lower frequencies than used in recently reported experiments.