Table of contents

A statistics of 1252 protons has been used to investigate the various characteristics of protons emitted with energies between (30-400) MeV in the interactions of 24 GeV/c protons and 50 GeV/c π^--mesons with emulsion nuclei. The characteristics of the emitted protons have been found to exhibit no dependence on the nature and energy of the incident particles. Thus the study of different features of protons has been carried out using the combined data from the two experiments.

The elastic scattering cross-section for ¹²C + ¹²C at 1016 MeV is analyzed in the optical model and in the Glauber model. Radial parameters characterizing the scattering are discussed.

With the aim of searching for high-spin configurations involving the high-j neutron orbitals, excited states in ²¹³Rn, ²¹⁵Ra and ²¹⁷Ra were populated in the bombardment of ²⁰⁸Pb with ¹³C ions. Gamma-ray singles, excitation functions and angular distributions, pulsed-beam-γ timing and γ-γ(t) coincidences were measured. Six isomeric levels were observed in ²¹³Rn, three in ²¹⁵Ra while none in ²¹⁷Ra. The lowest-lying 15/2^- states in all odd-A N = 127 isotones are de-excited by E3 transitions with a strength of about 23 W.u, suggesting that they are all coupled to the octupole phonon. In ²¹⁷Ra no evidence for collective behavior is found despite its closeness to the actinide region. The low-lying states in the level scheme can be interpreted as arising from three-neutron configurations. The wave function of a J^π = (37/2⁺) state in ²¹³Rn is proposed to include about 30% admixture from the two-octupole configuration πh_9/2³f_7/2 ⊗ vg_9/2 ⊗ (3^-)² since the de-exciting E3 transition has a strength of about 40 W.u. This is the first indication of such an excitation in the lead region.

We have calculated the normalized populations of 10 levels in the oxygen-like ions in optically thin medium, under steady state condition, by employing: (i) the incident electron energy dependent collision strengths, and (ii) the constant collision strength values at the incident electron energy E' (> ΔE_1,10). It is concluded that to calculate the intensity ratios for solar lines one can alternatively use the constant collision strengths at the electron energy E'.

The specific mass shift of the ionisation energy between ²⁰Ne and ²²Ne has been calculated using many-body perturbation theory. The first-order expectation value, neglecting relaxation effects is -41.0 GHz. Allowing for relaxation effects changes the result to -16.3 GHz, which, together with a lowest-order correlation effect of 9.3 GHz, gives a total result of -7.0 GHz. The experimental value is (-11 ± 3) GHz and the discrepancy is ascribed to higher-order correlation effects, which have not been evaluated.

We present results of many-electron calculations of the distribution of transition probability from doubly excited states of He over the radiative and radiationless decay channels. For He 2p3p³D, the calculated lifetime is τ_th = 0.107 × 10^-9 s compared with the beam-foil experimental value of τ = 0.115 ± 0.006 × 10^-9 s. Our value for the autoionization width (Γ = 0.61 × 10^-6 eV) differs significantly from those of three previously many-electron theories of resonances: 1.44 × 10^-6 eV, 2.72 × 10^-6 eV and 214 × 10^-6 eV.

The spectrum emitted from a nickel hollow cathode has been recorded with a Fourier transform spectrometer. Two dense groups of lines just above 18 000 Å have been identified as the transitions 3d⁸ (³F)5f-3d⁸ (³F)6g and 3d⁸ (³F)5g-3d⁸ (³F)6h in Ni II. The level structure of the configurations involved in these transitions has been studied by fitting the Slater parameters of the energy matrices to the observations. The fitted parameters have been used for calculating the relative line strengths in the transition arrays. Comparisons with the observed intensities show very good agreement.

The examination of the level values of the n = 2 configurations, which was recently carried through for ions iso-electronic with Li, Be, O and F, has now been extended to the configurations 2s²2p, 2s2p² and 2p³ of the boron sequence. In this study, expressions of the form A + B(Z - C)^-1 + a(Z - s)^x are derived for the difference between observed and theoretical values of selected level intervals, the theoretical values being based on the calculations of Cheng, Kim and Desclaux. By this procedure, accidental errors in the experimental data are smoothed out and missing data are interpolated or extrapolated beyond the range of observations. In the case of the two strongly interacting levels 2s2p²²S_1/2, ²P_1/2, however, the theory fails to reproduce the effects of the "avoided crossing" well enough to provide a useful frame of reference, and a more primitive method of extrapolation had to be used. The results of the examination are summarized in a table of recommended values for the 14 excited levels of the n = 2 complex, covering the range from Z = 7 to Z = 36, and a corresponding table of recalculated wavelengths, including intersystem combinations. Some experimental data reported in the literature are found to need revision.

Forty lines of S VII in the 601-1103 Å wavelength range are identified as transitions between the 2p⁵3s, 3p and 3d configurations. All energy levels in these configurations are determined. Their identification is confirmed by the results of a parametric calculation and an isoelectronic comparison.

The initial evolution of large-amplitude one-dimensional electron waves is investigated by applying a numerical simulation. The initial wave damping is found to be strongly enhanced relative to the linear damping, and it increases with increasing amplitude. The temporal evolution of the nonlinear damping rate γ(t) shows that it increases with time within the initial phase of propagation, t ≲ π/ω_B (ω_B is the bounce frequency), whereafter it decreases and changes sign implying a regrowth of the wave. The shift in the wave frequency δω is observed to be positive for t ≲ π/ω_B; then δω changes sign and oscillates around a negative asymptotic value. The results compare favourably with a recent theory by Sugihara et al. for the initial behaviour (t < π/ω_B).

Analytical results of the oppositely travelling waves (OTW) parametric decay instability in an inhomogeneous medium are presented. Generally accepted viewpoint about the convective nature of OTW parametric instability is shown to be valid only for relatively strong damping. Both for a strong and for a weak damping absolute instability takes place.

Stimulated Brillouin backscatter is considered as an example. For this instability spectrum of excited waves and increments are found.