Serban Misicu

Emission of electromagnetic radiation in α-decay

The electromagnetic radiation during the non-uniform motion of the fragments resulting from the α-decay of a heavy nucleus is computed in a time-dependent quantum formalism. The dynamical characteristics of the α-particle such as position, velocity and acceleration are computed by taking average values of the position and momentum operators and next the bremsstrahlung emission is determined by resorting to the classical formula for the radiation power. The contribution of the α-particle intra-barrier motion to the total bremsstrahlung yield is evaluated and some hints are given for the case when one considers α-decay from the ground state.

Neutronless -accompanied ternary fission of

A new type of decay corresponding to the neutronless -accompanied fragmentation of is studied. We employ a cluster model similar to the model used for the description of cluster radioactivity. No preformation factors were considered. The ternary relative isotopic yields were calculated as the ratio of the penetrability of a given ternary fragmentation over the sum of penetrabilities of all possible ternary neutronless fragmentations. The corresponding barriers between the light and heavy fragments and between the cluster and the two heavier fragments were computed with the help of a double-folding potential generated by M3Y-NN effective interaction and realistic fragment ground-state deformations. Also, we studied the influence of the fragment excitation energies on the yields, by including the level densities and the -stretching of the fragments. The new phenomenon could be experimentally observed by the triple-gamma coincidence technique between the fragments and .

Double fine structure in binary cold fission

We give a description of the binary cold fission process of 252Cf within the stationary scattering formalism. The decay of the dinuclear system (quasi-molecule) consists in the tunnelling of a metastable state from an internal region, where the nucleus–nucleus potential makes a quasi-molecular pocket due to the interplay of repulsive and attractive nuclear forces and the Coulomb force, to the asymptotic region which is governed solely by the Coulomb repulsion. As a transverse internal motion, we suppose angular oscillations of the fragments up to the scission point. In the external region these vibrations transform into rotations. The nuclear interaction is given by a double-folding procedure using M3Y forces plus a repulsive contact potential. For the experimental Q-value we find several resonant states of the binary system, depending on the repulsive strength. We predict a strong dependence of decay widths upon the internal structure of the considered resonant state. Therefore the measured yields of the two fragments with given angular momenta in coincidence are able to provide more insight into the internal molecular dynamics of the decaying dinuclear system.

Properties of some collective excitations in spherical nuclei from the superheavy island

We study the β-vibrational spectrum of the putative double magic superheavy nucleus 292120, as predicted by the relativistic mean-field (RMF) model in a phenomenological collective approach and compare it with the one of the well-known double magic heavy nuclei 208Pb. Results are also presented for the elements 300120 and 298114. We use a selection of different mean-field forces and discuss their different predictions and the consequences for the collective modes. In the framework of the macroscopic model for giant resonances we compute the transition densities of the isoscalar monopole, quadrupole and octupole, and isovector dipole modes for the superheavy element 292120, whose ground state density is determined from the RMF model. The results are also compared to those of 208Pb.

Molecular collective vibrations in the ternary neutronless fission of 252Cf

Based on a recent experimental finding which may suggest the existence of a tri-nuclear molecular structure before the cold ternary fragmentation of 252Cf takes place, we solved the eigenvalue problem of a certain class of vibrations which are very likely to occur in these molecules. These oscillations are the result of the joint action of rotations of the heavier fragments and the transversal vibrations of the lighter spherical cluster with respect to the fission axis. In the calculation of the interaction between the heavier fragments we took into account higher multipole deformations, including the hexadecupole one, and introduced a repulsive nuclear part to ensure the creation of a potential pocket in which a few molecular states can be accommodated. The possibility to observe the de-excitation of such states is discussed in connection with the molecular lifetime.

Orientations of fragments emitted in binary cold fission of 252Cf

The dependence of the driving potential on the orientation of fragments at scission is investigated for the case of cold fission of 252Cf. It is shown that in the case of cold fission the fragments exclusively emerge at scission in the pole–pole configuration. However, quantum fluctuations enable small deviations from this configuration during the tunnelling process. The mass yields of fission fragment pairs in the cold fission of 252Cf are computed for pole–pole and equator–equator orientations and are compared to the experimental data.

Collective modes of tri-nuclear molecules

A geometrical model for tri-nuclear molecules is presented. An analytical solution is obtained provided the nuclei, which are taken to be prolately deformed, are connected in line to each other. Furthermore, the tri-nuclear molecule is composed of two heavy and one light cluster, the latter sandwiched between the two heavy clusters. A basis is constructed in which Hamiltonians of more general configurations can be diagonalized. In the calculation of the interaction between the clusters higher multipole deformations are taken into account, including the hexadecupole one. A repulsive nuclear core is introduced in the potential in order to ensure a quasi-stable configuration of the system. The model is applied to three nuclear molecules, namely 96Sr + 10Be + 146Ba, 108Mo + 10Be + 134Te and 112Ru + 10Be + 130Sn.

Quantum dissipation in cluster decay phenomena: I. Smoothly joined quadratic potentials

This paper is devoted to the study of quantum dissipation in nuclear cluster decay phenomena within the framework of the Lindblad approach to quantum open systems. Typical examples of nuclear decay phenomena, such as cluster radioacivity, spontaneous cold fission of actinide nuclei or quasi-fission of super-heavy nuclei can be described by considering the tunnelling of a metastable state across a piecewise quadratic potential. Two study cases are considered: (i) a harmonic well smoothly joined to an inverted parabola which simulates the barrier and (ii) the inverted parabola of case (i) is continued with a second harmonic well. The width and depth of the second harmonic oscillator well are varied over a wide range of values in order to encompass particular cases of tunnelling in the double-well potential. The evolution of the averages and covariances of the quantum sub-system is studied in both under- and over-damped regimes. For a Gaussian initial wavepacket we compute the tunnelling probability for different values of the friction coefficient and fixed values of the diffusion coefficients. The ansatz used for these coefficients corresponds to the case with temperature T = 0.