[en] The angular momentum built up in the fragment nuclei during a damped nuclear reaction is subsequently lost through decay. Since the decay is very fast, the only way to learn about the angular momentum accumulated in the nuclei is to observe the sequential decay products. The present investigation aims at providing precise methods for calculating properties of the sequential decay on the basis of primary spin distributions calculated with the transfer theory

[en] The dynamical evolution of the correlated angular momentum distribution in a damped nuclear reaction is discussed within the framework of the nucleon exchange transport model. 13 references

[en] An important goal in the theory of nuclear dynamics is to understand the observed transport phenomena in terms of the basic microscopic processes in the system. For this purpose a model was developed in which the dissipative mechanism responsible for the transport process is the transfer of nucleons between the two reacting nuclides. Until now, most efforts to confront that theory with data have concentrated on the evolution of the charge and mass distribution with energy loss, and overall good agreement has been obtained for a variety of features. While this success lends strong support to the theory, it is important to broaden the contact with experiment by considering also other aspects of the data. Therefore the authors have undertaken a comprehensive study of the angular momentum variables which represent six additional observables (three for each fragment spin) and thus provide a rich testing ground for the theory

[en] Theories of damped nuclear reactions are often expressed in terms of degrees of freedom which are familiar from simpler nuclear reactions, such as surface vibrations and nuclear transfer. However, the clean characteristics of such elementary nuclear excitations are largely washed out due to the complexity of a damped reaction where high excitations and large distortions occur. The experimental study of damped nuclear reactions is therefore, with few exceptions, limited to observables subject to overall conservation after the reaction: the mass and charge number, the momentum and energy, and the angular momentum. (Parity is also conserved but is of little use.) If the induced elementary nuclear excitations carry significant amounts of a particular observable, the distribution of this observable in the reaction complex may reach the asymptotic (long-time) limit, for which the distribution in this observable is statistical. For the angular momentum observables it is clear from experiment that the mean spin vectors do not generally reach their equilibrium values. But the statistical limit has been advocated for describing the high spin variances. Comparisons between experiment and theory are reported for angular correlations for ⁸⁶Kr reactions

[en] The evolution of the angular momentum distribution in damped nuclear reactions is discussed within the framework of the nucleon exchange transport model. First order equations are derived for the time evolution of the mean values and covariances of the spin variables. Solutions are given for 1400 MeV ¹⁶⁵Ho + ¹⁶⁵Ho reactions at various values of total angular momentum and total kinetic energy loss. Spin dispersions are well described by the calculations

[en] A schematic model for the mixing of rotational bands above the yrast line in well deformed nuclei is considered. Many-particle configurations of a rotating mean field form basis bands, and these are subsequently mixed due to a two body residual interaction. The energy interval over which a basis band is spread out increases with increasing excitation energy above the yrast line. Conversely, the B(E2) matrix element for rotational decay out of one of the mixed band states is spread over an interval which is predicted to become more narrow with increasing excitation energy. Finally, the implication of band mixing for γ-ray energy correlations is briefly discussed. (orig.)

[en] The damping of collective rotational motion is studied microscopically, making use of shell model calculations based on the cranked Nilsson deformed mean-field and on residual two-body interactions, and focusing on the shape of the gamma-gamma correlation spectra and on its systematic behavior. It is shown that the spectral shape is directly related to the damping width of collective rotation, Γ_rot, and to the spreading width of many-particle many-hole configurations, Γ_μ. The rotational damping width is affected by the shell structure, and is very sensitive to the position of the Fermi surface, besides mass number, spin and deformation. This produces a rich variety of features in the rotational damping phenomena

[en] The parameters of the charge distribution of the fission fragments are calculated as functions of the mass ratio of the fragments and the excitation energy at deformations between the saddle point and scission. The scission region is parametrized in terms of connected shapes. The non-uniformity of the LDM charge density for such connected shapes is considered as a new collective coordinate in fission. Reasonable agreement with experimental data is obtained. (Auth.)

[en] The particle-vibration coupling formalism is generalized to deal with hot, strongly rotating nuclei. In this way the basis to carry out a microscopic description of the structure of compound nuclei has been developed, in particular the calculation of the effective mass of nucleons close to the Fermi energy. As a consequence, it will be possible to provide a realistic estimate of the nuclear level density as a function of rotational frequency and temperature, a quantity which is among the key ingredients needed in the study of the evolution of the cooling of the compound nucleus through nucleon and γ-decay

[en] Properties of warm nuclear states are discussed. First, the γ decay flow deexciting the states in discussed qualitatively, with emphasis on the competition between E1 and E2 transitions, and the phase transition between undamped and damped rotation. The formalism of rotational damping is briefly reviewed, and subsequently applied to a realistic calculation of the rotational damping width Γ_rot for the nucleus ¹⁶⁸ Yb_j using the cranked Nilsson potential. The calculated values are found to be in agreement with recent preliminary data. (orig.)