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A. Sandulescu

Publications and source records attributed to A. Sandulescu.

At least 19 recordsLinked to original sources
arXiv2010

Magic radioactivity of 252Cf

We show that the sharp maximum corresponding to 107Mo in the fragment distribution of the 252Cf cold fission is actually a Sn-like radioactivity, similar to other decay processes in which magic nuclei are involved, namely alpha-decay and heavy cluster emission, also called Pb-like radioactivity. It turns out that the mass asymmetry degree of freedom has a key role in connecting initial Sn with the final Mo isotopes along the fission path. We suppose the cold rearrangement of nucleons within the framework of the two center shell model, in order to compute the cold valleys in the charge equilibrated fragmentation potential. The fission yields are estimated by using the semiclassical penetration approach. We consider five degrees of freedom, namely the inter-fragment distance, the shapes of fragments, the neck parameter and mass asymmetry. We found an isomeric minimum between the internal and external barriers. It turns out that the inner cold valley of the total potential energy is connected to the double magic isotope 132Sn

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arXiv2009

Microscopic description of Cf-252 cold fission yields

We investigate the cold fission of 252Cf within the two center shell model to compute the potential energy surface. The fission yields are estimated by using the semiclassical penetration approach. It turns out that the inner cold valley of the total potential energy is strongly connected with Z=50 magic number. The agreement with experimental values is very much improved only by considering mass and charge asymmetry degrees of freedom. Thus, indeed cold fission of 252Cf is a Sn-like radioactivity, related the other two "magic radioactivities", namely alpha-decay and heavy-cluster decay, called also Pb-like radioactivity. This calculation provides the necessary theoretical confidence to estimate the penetration cross section in producing superheavy nuclei, by using the inverse fusion process.

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arXiv2008

Synthesis of superheavy elements beyond Z=118

We investigate the cold fission/fusion paths of superheavy nuclei within the two center shell model, in order to find the best projectile-target combinations of their production. The fission/fusion yields are estimated by using the semiclassical approach. We predict several asymmetric combinations of relative long living fragments, which can be used in fusion experiments of superheavy nuclei with Z>118.

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arXiv2007

Lindblad master equation for the damped harmonic oscillator with deformed dissipation

In the framework of the Lindblad theory for open quantum systems, a master equation for the quantum harmonic oscillator interacting with a dissipative environment, in particular with a thermal bath, is derived for the case when the interaction is based on deformed algebra. The equations of motion for observables strongly depend on the deformation function. The expectation values of the number operator and squared number operator are calculated in the limit of a small deformation parameter for the case of zero temperature of the thermal bath. The steady state solution of the equation for the density matrix in the number representation is obtained and its independence of the deformation is shown.

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arXiv2006

Purity and decoherence in the theory of a damped harmonic oscillator

For the generalized master equations derived by Karrlein and Grabert for the microscopic model of a damped harmonic oscillator, the conditions for purity of states are written, in particular for different initial conditions and different types of damping, including Ohmic, Drude and weak coupling cases, Agarwal and Weidlich-Haake models. It is shown that the states which remain pure are the squeezed states with constant in time variances. For pure states, the generalized nonlinear Schr\" odinger-type equations corresponding to these master equations are also obtained. Then the condition for purity of states of a damped harmonic oscillator is considered in the framework of Lindblad theory for open quantum systems. For a special choice of the environment coefficients, the correlated coherent states with constant variances and covariance are shown to be the only states which remain pure all the time during the evolution of the considered system. In Karrlein-Grabert and Lindblad models, as well as in the considered particular models, the expressions of the rate of entropy production is written and it is shown that the states which preserve their purity in time are also the states which minimize the entropy production and, therefore, they are the most stable ones under evolution in the presence of the environment and play an important role in the description of decoherence phenomenon.

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arXiv2006

On the damping of the angular momentum of three harmonic oscillators

In the frame of the Lindblad theory of open quantum systems, the system of three uncoupled harmonic oscillators with opening operators linear in the coordinates and momenta of the considered system is analyzed. The damping of the angular momentum and of its projection is obtained.

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arXiv2006

Damped quantum harmonic oscillator

In the framework of the Lindblad theory for open quantum systems the damping of the harmonic oscillator is studied. A generalization of the fundamental constraints on quantum mechanical diffusion coefficients which appear in the master equation for the damped quantum oscillator is presented; the Schrödinger and Heisenberg representations of the Lindblad equation are given explicitly. On the basis of these representations it is shown that various master equations for the damped quantum oscillator used in the literature are particular cases of the Lindblad equation and that the majority of these equations are not satisfying the constraints on quantum mechanical diffusion coefficients. Analytical expressions for the first two moments of coordinate and momentum are also obtained by using the characteristic function of the Lindblad master equation. The master equation is transformed into Fokker-Planck equations for quasiprobability distributions. A comparative study is made for the Glauber $P$ representation, the antinormal ordering $Q$ representation and the Wigner $W$ representation. It is proven that the variances for the damped harmonic oscillator found with these representations are the same. By solving the Fokker-Planck equations in the steady state, it is shown that the quasiprobability distributions are two-dimensional Gaussians with widths determined by the diffusion coefficients. The density matrix is represented via a generating function, which is obtained by solving a time-dependent linear partial differential equation derived from the master equation. Illustrative examples for specific initial conditions of the density matrix are provided.

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arXiv2004

Open quantum systems

The damping of the harmonic oscillator is studied in the framework of the Lindblad theory for open quantum systems. A generalization of the fundamental constraints on quantum mechanical diffusion coefficients which appear in the master equation for the damped quantum oscillator is presented; the Schrödinger, Heisenberg and Weyl-Wigner-Moyal representations of the Lindblad equation are given explicitly. On the basis of these representations it is shown that various master equations for the damped quantum oscillator used in the literature are particular cases of the Lindblad equation and that not all of these equations are satisfying the constraints on quantum mechanical diffusion coefficients. The master equation is transformed into Fokker-Planck equations for quasiprobability distributions and a comparative study is made for the Glauber $P$ representation, the antinormal ordering $Q$ representation and the Wigner $W$ representation. The density matrix is represented via a generating function, which is obtained by solving a time-dependent linear partial differential equation derived from the master equation. The damped harmonic oscillator is applied for the description of the charge equilibration mode observed in deep inelastic reactions. For a system consisting of two harmonic oscillators the time dependence of expectation values, Wigner function and Weyl operator are obtained and discussed. In addition models for the damping of the angular momentum are studied. Using this theory to the quantum tunneling through the nuclear barrier, besides Gamow's transitions with energy conservation, additional transitions with energy loss, are found. When this theory is used to the resonant atom-field interaction, new optical equations describing the coupling through the environment are obtained.

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arXiv2000

On scission configuration in ternary fission

A static scission configuration in cold ternary fission has been considered in the framework of two mean field approaches. The virial theorems has been suggested to investigate correlations in the phase space, starting from a kinetic equation. The inverse mean field method is applied to solve single-particle Schredinger equation, instead of constrained selfconsistent Hartree-Fock equations. It is shown, that it is possible to simulate one-dimensional three-center system via inverse scattering method in the approximation of reflectless single-particle potentials

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arXiv2000

Molecular Collective Vibrations in the Ternary Neutronless Fission of $^{252}$Cf

Based on a recent experimental finding which may suggest the existence of a tri-nuclear molecular structure before the cold ternary fragmentation of $^{252}$Cf 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 joined 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 insure 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 life-time.

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arXiv2000

Angular Momenta of Even-Even Fragments in the Neutronless Fission of $^{252}$Cf

The recent advent of experimental techniques in which the dynamical characteristics of fission fragments are determined more accurately, prompted us to investigate the angular momentum acquired by fragments in a model which describes the cold(neutronless) fission of $^{252}$Cf as the decay of a giant nuclear molecule. The molecular configuration is a consequence of the interplay between the attractive nuclear part and the repulsive Coulomb+nuclear forces. The basic ideea of the present approach is to separate the radial(fission) modes describing the decay of the molecule from the modes associated to transversal vibrations(bending) of the fragments. The distance between the centers of the two fragments is fixed by the requirement that the energy released in the fission reaction $Q$, equals the sum of quantum zero-energies of radial and transversal modes and the total excitation energy $E^*$. Using a semiclassical coupled channel formalism we computed the additional angular momenta acquired by the fragments during their post-scission motion, and found that the Coulomb excitation accounts for less than 10% of the final spins.

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arXiv2000

Shift of the 2$^+_1$ state of $^{10}$Be in the ternary cold fission of $^{252}$Cf

Recent experimental data indicate that in the ternary cold fission of $^{252}$Cf the energy of the first excited state of the accompanying light cluster $^{10}$Be is decreased by an amount ranging between $\approx$ 6 and 26 keV. A model is proposed to calculate the shift of the vibrational 2$^+_1$ state in $^{10}$Be when its heavy companions are the even-even nuclei $^{146}$Ba and $^{96}$Sr. The stiffness parameters of the $β$-vibrations are calculated within the self-consistent Hartree-Fock method with BCS pairing correlations taken into account, and its change is determined by the interaction of the light cluster with the heavy fragments. The results are pointing to a dependence of the shift magnitude and signature on the relative distance between the three clusters and their mutual orientation. Eventually it is the anharmonic perturbation of the spherical vibrator which is responsible for obtaining a negative energy shift of the 2$^+_1$ state.

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arXiv1999

Ternary configuration in the framework of inverse mean-field method

A static scission configuration in cold ternary fission has been considered in the framework of mean field approach. The inverse scattering method is applied to solve single-particle Schroedinger equation, instead of constrained selfconsistent Hartree-Fock equations. It is shown, that it is possible to simulate one-dimensional three-center system via inverse scattering method in the approximation of reflectless single-particle potentials.

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arXiv1999

Nonlinear waves of nuclear density

Nonlinear excitations of nuclear density are considered in the framework of semiclassical nonlinear nuclear hydrodynamics. Possible types of stationary nonlinear waves in nuclear media are analysed using Nonlinear Schroedinger equation of fifth order and classified using a simple mechanical picture. It is shown that a rich spectrum of nonlinear oscillations in one-dimensional nuclear medium exist.

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arXiv1998

Long Range Alpha the Ternary Cold Fission of $^{252}$Cf

We compute the final kinetic energies of the fragments emitted in the light charged particle accompanied cold fission of $^{252}$Cf taking into account the ground state quadrupole deformation and the finite-size effects of the fragments and integrating the equations of motion for a three-body system subjected only to Coulomb forces. The initial conditions for the trajectory calculations were derived in the frame of a deformed cluster model which includes also the effect due to the absorbative nuclear part. Although the distributions of initial kinetic energies is rather broad we show that in cold fission the initial conditions can be better determined than in the usual spontaneous fission.

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arXiv1998

Neutronless $^{10}$be-Accompanied Ternary Fission of $^{252}$Cf}

A new type of decay corresponding to the neutronless $^{10}$Be-accompanied fragmentation of $^{252}$Cf 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 fragment and between the $^{10}$Be 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 $β$-stretching of the fragments. The new phenomenon could be experimentally observed by the triple gamma coincidence technique between the fragments and $^{10}$Be.

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arXiv1998

Role of Fragment Higher Static Deformations in the Cold Binary Fission of $^{252}$Cf

We study the binary cold fission of $^{252}$Cf in the frame of a cluster model where the fragments are born to their respective ground states and interact via a double-folded potential with deformation effects taken into account up to multipolarity $λ=4$. The preformation factors were neglected. In the case when the fragments are assumed to be spherical or with ground state quadrupole deformation, the $Q$-value principle dictates the occurence of a narrow region around the double magic $^{132}$Sn, like in the case of cluster radioactivity. When the hexadecupole deformation is turned on, an entire mass-region of cold fission in the range 138 - 156 for the heavy fragment arise, in agreement with the experimental observations. This fact suggests that in the above mentioned mass-region, contrary to the usual cluster radioactivity where the daughter nucleus is always a neutron/proton (or both) closed shell or nearly closed shell spherical nucleus, the clusterization mechanism seems to be strongly influenced by the hexadecupole deformations rather than the $Q$-value.

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