Search results for " approximation"
showing 10 items of 575 documents
Polarization corrections to single-particle energies studied within the energy-density-functional and quasiparticle random-phase approximation approa…
2014
Background: Models based on using perturbative polarization corrections and mean-field blocking approximation give conflicting results for masses of odd nuclei. Purpose: We systematically investigate the polarization and mean-field models, implemented within self-consistent approaches that use identical interactions and model spaces, to find reasons for the conflicts between them. Methods: For density-dependent interactions and with pairing correlations included, we derive and study links between the mean-field and polarization results obtained for energies of odd nuclei. We also identify and discuss differences between the polarization-correction and full particle-vibration-coupling (PVC) …
Two-neutrino ββ decay to excited states. The 0+ → 2+ decay of 136Xe
1993
Abstract A method to calculate the two-neutrino double beta decay (2vββ) to one-phonon excited states is presented. The formalism, which is based on the quasiparticle random phase approximation, is applied to the description of the 2vββ transition 136Xe (0 g.e. + ) → 136 Ba (2 1 + ). It is shown that the participant matrix element is not suppressed by the inclusion of renormalized particle-particle interactions.
Collective subspaces for large amplitude motion and the generator coordinate method
1979
The collection path $|\ensuremath{\varphi}(q)〉$ to be used in a microscopic description of large amplitude collective motion is determined by means of the generator coordinate method. By varying the total energy with respect to $|\ensuremath{\varphi}(q)〉$ and performing an adiabatic expansion a hierarchy of equations is obtained which determines uniquely a hierarchy of collective paths with increasing complexity. To zeroth order the $|\ensuremath{\varphi}(q)〉$ are Slater determinants, to first order they include 2p-2h correlations. In both cases simple noninterative prescriptions for an explicit construction of the path are derived. For a correlated path their solutions agree at the Hartree…
Multipole strength inC12from the (e,e’α) reaction for momentum transfers up to 0.61fm−1
1995
We have excited the giant resonance region in $^{12}\mathrm{C}$ via inelastic electron scattering, and have measured the first complete angular correlations for charged particle emission for this reaction for four values of momentum transfer ranging from 0.24 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$ to 0.61 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$. By analyzing the \ensuremath{\alpha}-emission channels via the Legendre and resonance formalisms, we unambiguously determined the multipole contributions to the total cross section for \ensuremath{\alpha} emission to the ground state of $^{8}\mathrm{Be}$, and have set limits on these contributions for \ensuremath{\alpha} emission to the first…
Nuclear matrix elements of ββ decay from β-decay data
2005
Abstract The evaluation of the nuclear matrix elements (NME) of the two-neutrino double beta ( 2 ν β β ) decay and neutrinoless double beta ( 0 ν β β ) decay using the proton–neutron quasiparticle random-phase approximation (pnQRPA) is addressed. In particular, the extraction of a proper value of the proton–neutron particle–particle interaction parameter, g pp , of this theory is analyzed in detail. Evidence is shown, that it can be misleading to use the experimental half-life of the 2 ν β β decay to extract a value for g pp . Rather, arguments are given in favour of using the available data on single beta decay for this purpose.
Test of the proton-neutron random-phase approximation method within an extended Lipkin-type model
2001
An extended Lipkin-Meshkov-Glick model for testing the proton-neutron random-phase approximation $(pn\mathrm{RPA})$ method is developed, taking into account explicitly proton and neutron degrees of freedom. Besides the proton and neutron single-particle terms two types of residual proton-neutron interactions, one simulating a particle-particle and the other a particle-hole interaction, are included in the model Hamiltonian so that the model is exactly solvable in an isospin $\mathrm{SU}(2)\ensuremath{\bigotimes}\mathrm{SU}(2)$ basis. The behavior of the first excited (collective) state obtained by (i) exact diagonalization of the Hamiltonian matrix and (ii) with the $\mathrm{pn}\mathrm{RPA}…
Non-perturbative renormalization of lattice operators in coordinate space
2004
We present the first numerical implementation of a non-perturbative renormalization method for lattice operators, based on the study of correlation functions in coordinate space at short Euclidean distance. The method is applied to compute the renormalization constants of bilinear quark operators for the non-perturbative O(a)-improved Wilson action in the quenched approximation. The matching with perturbative schemes, such as MS-bar, is computed at the next-to-leading order in continuum perturbation theory. A feasibility study of this technique with Neuberger fermions is also presented.
Investigation of the decay of to excited states in
1996
The two-neutrino mode of double beta decay of is investigated both theoretically and experimentally. The calculations, using the quasiparticle random phase approximation approach, show that for the detection of transitions to the two first excited states in the daughter nuclide will be possible in the very near future. On the experimental side, new, most stringent limits on half-lives for the double beta decay of to excited states in have been obtained with a `well-type' germanium detector. They range between and years (90% CL).
New region of deformation in the neutron-rich 60 24Cr36 and 62 24Cr38
2003
The neutron-rich nuclei 23 60-63V have been produced at GANIL via interactions of a 61.8A·MeV 76Ge beam with a 58Ni target. Beta-decay to 24 60-63Cr has been investigated using combined β- and γ-ray spectroscopy. Half-lives of the 60-63V nuclei have been determined, and the existence of a beta-decay isomer in the 60V nucleus is strongly supported. The observation of low-energy 2+ states in 60Cr (646keV) and 62Cr (446keV) suggests that these isotopes are strongly deformed with β2 ∼ 0.3. This is confirmed by shell model calculations which show the dominant influence of the intruder g and d orbitals to obtain low 2+ energies in the neutron-rich Cr isotopes.
β-delayed neutron decay of 104Y, 112Tc, 113Tc and 114Tc: test of half-life predictions for neutron-rich isotopes of refractory elements
1999
Abstract Beta-decay gross properties of neutron-rich isotopes 104Y and 112,113,114Tc produced in 25 MeV proton-induced fission of 238U have been measured. Decays of 104Y with a half-life of 180±60 ms and of 114Tc with a half-life of 150±30 ms are reported for the first time. Beta-delayed neutron emission probabilities of 112,113,114Tc are determined as (1.5±0.2)%, (2.1±0.3)% and (1.3±0.4)%, respectively. Comparison of the observed Pn values with a recent theoretical calculation based on deformed quasiparticle random phase approximation (QRPA) shows good overall agreement for Tc isotopes. However, comparison of beta-decay half-lives of neutron-rich isotopes of Y to Rh with the QRPA model and…