10 research outputs found
Thermodynamics of pairing in mesoscopic systems
Using numerical and analytical methods implemented for different models we
conduct a systematic study of thermodynamic properties of pairing correlation
in mesoscopic nuclear systems. Various quantities are calculated and analyzed
using the exact solution of pairing. An in-depth comparison of canonical, grand
canonical, and microcanonical ensemble is conducted. The nature of the pairing
phase transition in a small system is of a particular interest. We discuss the
onset of discontinuity in the thermodynamic variables, fluctuations, and
evolution of zeros of the canonical and grand canonical partition functions in
the complex plane. The behavior of the Invariant Correlational Entropy is also
studied in the transitional region of interest. The change in the character of
the phase transition due to the presence of magnetic field is discussed along
with studies of superconducting thermodynamics.Comment: 19 pages, 24 figure
Nuclear Schiff moment and soft vibrational modes
The atomic electric dipole moment (EDM) currently searched by a number of
experimental groups requires that both parity and time-reversal invariance be
violated. According to current theoretical understanding, the EDM is induced by
the nuclear Schiff moment. The enhancement of the Schiff moment by the
combination of static quadrupole and octupole deformation was predicted
earlier. Here we study a further idea of the possible enhancement in the
absence of static deformation but in a nuclear system with soft collective
vibrations of two types. Both analytical approximation and numerical solution
of the simplified problem confirm the presence of the enhancement. We discuss
related aspects of nuclear structure which should be studied beyond mean-field
and random phase approximations.Comment: 14 pages, 4 figure
Neutron Correlations in the Decay of the First Excited State of 11Li
The decay of unbound excited 11Li was measured after being populated by a two-proton removal from a 13B beam at 71 MeV/nucleon. Decay energy spectra and Jacobi plots were obtained from measurements of the momentum vectors of the 9Li fragment and neutrons. A resonance at an excitation energy of âŒ1.2 MeV was observed. The kinematics of the decay are equally well fit by a simple dineutron-like model or a phase-space model that includes final state interactions. A sequential decay model can be excluded
Chaotic wave functions and exponential convergence of low-lying energy eigenvalues
We suggest that low-lying eigenvalues of realistic quantum many-body
hamiltonians, given, as in the nuclear shell model, by large matrices, can be
calculated, instead of the full diagonalization, by the diagonalization of
small truncated matrices with the exponential extrapolation of the results. We
show numerical data confirming this conjecture. We argue that the exponential
convergence in an appropriate basis may be a generic feature of complicated
("chaotic") systems where the wave functions are localized in this basis.Comment: 4 figure
The role of E1-E2 interplay in multiphonon Coulomb excitation
In this work we study the problem of a charged particle, bound in a
harmonic-oscillator potential, being excited by the Coulomb field from a fast
charged projectile. Based on a classical solution to the problem and using the
squeezed-state formalism we are able to treat exactly both dipole and
quadrupole Coulomb field components. Addressing various transition amplitudes
and processes of multiphonon excitation we study different aspects resulting
from the interplay between E1 and E2 fields, ranging from classical dynamic
polarization effects to questions of quantum interference. We compare exact
calculations with approximate methods. Results of this work and the formalism
we present can be useful in studies of nuclear reaction physics and in atomic
stopping theory.Comment: 10 pages, 6 figure
α-cluster resonances in light nuclei
Thick target inverse kinematics technique was combined with Time of Flight method to study resonance reactions induced by heavy ions at low energy, to minimize background and to identify various possible nuclear processes in extended target. The 17O, 20Ne spectrum, the cluster and nucleon spectroscopic factors were calculated using cluster-nucleon configuration interaction model
Non-exponential and oscillatory decays in quantum mechanics
The quantum-mechanical theory of the decay of unstable states is revisited. We show that the decay is non-exponential both in the short-time and long-time limits using a more physical definition of the decay rate than the one usually used. We report results of numerical studies based on Winter's model that may elucidate qualitative features of exponential and non-exponential decay more generally. The main exponential stage is related to the formation of a radiating state that maintains the shape of its wave function with exponentially diminishing normalization. We discuss situations where the radioactive decay displays several exponents. The transient stages between different regimes are typically accompanied by interference of various contributions and resulting oscillations in the decay curve. The decay curve can be fully oscillatory in a two-flavor generalization of Winter's model with some values of the parameters. We consider the implications of that result for models of the oscillations reported by GSI