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DYNAMICAL STUDY OF PROTON EMISSION FROM DEFORMED NUCLEI

Margarit Rizea, N. Cârjan

Published Jan 1, 2008• 2 citations
OpenAlex

Abstract

The most intuitive and direct way to study proton emission from unbound nuclear states is to start with a proton wave packet localized inside the well of the p-nucleus interacting potential and follow its time evolution by solving numerically the time-dependent Schrödinger equation (TDSE). Then the physical properties of the decaying system can be inferred from its solution. The most important calculable quantities are: the tunneling probability and the decay rate. In the present paper we consider bi-dimensional axially symmetric nuclear shapes, allowing the treatment of both spherical and deformed nuclei. The solution of TDSE is obtained by the Crank-Nicolson method. We discuss also the treatment of numerical boundary conditions, the preparation of the initial wave function as a quasi-stationary state and the calculation of the decay rate using the flux. In application we reveal the influence of the deformation on the decay rate.

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The most intuitive and direct way to study proton emission from unbound nuclear states is to start with a proton wave packet localized inside the well of the p-nucleus interacting potential and follow its time evolution by solving numerically the time-dependent Schrödinger equation (TDSE). Then the physical properties of the decaying system can be inferred from its solution. The most important calculable quantities are: the tunneling probability and the decay rate. In the present paper we consider bi-dimensional axially symmetric nuclear shapes, allowing the treatment of both spherical and deformed nuclei. The solution of TDSE is obtained by the Crank-Nicolson method. We discuss also the treatment of numerical boundary conditions, the preparation of the initial wave function as a quasi-stationary state and the calculation of the decay rate using the flux. In application we reveal the influence of the deformation on the decay rate.
The time evolution of single proton quasi-stationary states emitted from axially deformed nuclei is studied by solving numerically the two-dimensional time dependent Schrödinger equation. Angular distributions of emission with respect to the nuclear axis of symmetry are obtained. It is shown that the main escape paths are determined by the quantum numbers of the metastable state, rather than by the deformation of the potential. Combinations of such numerical studies of multidimensional quantum tunneling and angular distribution measurements from oriented deformed nuclei could provide invaluable nuclear structure information and imaging of Nilsson orbitals.
Based on a single particle model which describes the time evolution of the wave function during tunneling across a one dimensional potential barrier we study the proton decay of 208^{208}208Pb from excited states with non-vanishing angular momentum ell\\ellell. Several quantities of interest in this process like the decay rate lambda\\lambdalambda, the period of oscillation ToscT_{osc}Tosc​, the transient time ttrt_{tr}ttr​, the tunneling time ttunt_{tun}ttun​ and the average value of the proton packet position $ r_{av} $ are computed and compared with the WKB results.
This project looks into the time evolution of a wave function within a two-dimensional quantum well. We start by solving the time-dependent Schrödinger equation for stationary states in a quantum well. Next, we express any wave function as a linear combination of stationary states, allowing us to understand their time evolution. Two methods are presented: one relies on decomposing the wave function into a basis of stationary states and the other on discretisation of the time-dependent Schrödinger equation, incorporating three-point formulas for derivatives. These approaches necessitate confronting intricate boundary conditions and require maintaining energy conservation for numerical accuracy. We further demonstrate the methods using a wave packet, revealing fundamental phenomena in quantum physics. Our results demonstrate the utility of these methods in understanding quantum systems, despite the challenges in determining stationary states for a given potential. This study enhances our comprehension of the dynamics of quantum states in constrained systems, essential for fields like quantum computing and nanotechnology.
The nuclear dissipation, i.e. the conversion of collective energy into intrinsic energy is investigated in the frame of quantum mechanics. Using appropiate numerical procedures, we follow the motion of individual nucleons according to the time-dependent Schr̈odinger equation with time-dependent potential. In particular we study the transition from the saddle to the scission point during the low energy fission of 236U. Different rates T of change of the nuclear shape along this path were considered. The overlap integrals between the static solutions of the bi-dimensional Schr̈odinger equation and the time-dependent wave packets yield the transition probabilities and hence the singleparticle excitations during the saddle-to-scission descent. Using the numerical solutions other relevant pre-scission properties have been evaluated as well.
Recently we outlined an analytical method of solving the time-dependent Schr\"odinger equation for a model which simulates a decaying quantum system such as an $\ensuremath{\alpha}$-decaying nucleus. A particle in the model is initially confined around the origin and leaks out, tunneling through a potential barrier. The solution can be expressed as a linear combination of the Moshinsky functions, each of which is associated with a pole of the scattering S\mathbf{S}S matrix of the model. In this paper we give a full account of the method with a few explicit examples. We examine deviations from the exponential decay law at very large times. We comment on a recent controversy regarding the t dependence of the survival and nonescape probabilities when t is very large.