Search results for "ASIP"
showing 10 items of 322 documents
Kerman-Onishi conditions in self-consistent tilted-axis-cranking mean-field calculations
2013
\item[Background] For cranked mean-field calculations with arbitrarily oriented rotational frequency vector $\boldsymbol{\omega}$ in the intrinsic frame, one has to employ constraints on average values of the quadrupole-moment tensor, so as to keep the nucleus in the principal-axis reference frame. Kerman and Onishi [Nucl. Phys. A {\bf 361}, 179 (1981)] have shown that the Lagrangian multipliers that correspond to the required constraints are proportional to $\boldsymbol{\omega} \times \boldsymbol{J}$, where $\boldsymbol{J}$ is the average angular momentum vector. \item[Purpose] We study the validity and consequences of the Kerman-Onishi conditions in the context of self-consistent tilted-a…
Microscopic description of low-lying two-phonon states: Electromagnetic transitions
2003
Microscopic description of low-lying two-phonon states in even-even nuclei is introduced. The main building blocks are the quasiparticle random-phase approximation (QRPA) phonons. A realistic microscopic nuclear Hamiltonian, based on the Bonn one-boson-exchange potential, is diagonalized in a basis containing one-phonon and two-phonon components, coupled to a given angular momentum and parity. The QRPA equations are directly used in deriving the equations of motion for the two-phonon states. The Pauli principle is taken into account by diagonalizing the metric matrix and discarding the zero-norm states. The electromagnetic transition matrix elements are derived in terms of the metric matrix…
K-isomeric state in even-even100Sr
1995
A t1/2=85 ns isomer has been identified at 1619 keV in100Sr. The halflife is attributed to a ΔK=4 hindered decay. The configuration is proposed to be built on the [411]3/2 and the [532]5/2 neutron quasiparticle orbitals.
Emergent Soft Monopole Modes in Weakly-Bound Deformed Nuclei
2014
Based on the Hartree-Fock-Bogoliubov solutions in large deformed coordinate spaces, the finite amplitude method for quasiparticle random phase approximation (FAM-QRPA) has been implemented, providing a suitable approach to probe collective excitations of weakly-bound nuclei embedded in the continuum. The monopole excitation modes in Magnesium isotopes up to the neutron drip line have been studied with the FAM-QRPA framework on both the coordinate-space and harmonic oscillator basis methods. Enhanced soft monopole strengths and collectivity as a result of weak-binding effects have been unambiguously demonstrated.
Low-lying collective states inRu98–106isotopes studied using a microscopic anharmonic vibrator approach
2003
Anharmonic features of the low-lying collective states in the $^{98--106}\mathrm{Ru}$ isotopes have been investigated systematically by using the microscopic anharmonic vibrator approach (MAVA). MAVA is based on a realistic microscopic $G$-matrix Hamiltonian, only slightly renormalized in the adopted large realistic single-particle spaces. This Hamiltonian is used to derive equations of motion for the mixing of one- and two-phonon degrees of freedom starting from collective phonons of the quasiparticle random-phase approximation. Analysis of the level energies and the electric quadrupole decays of the two-phonon type of states indicates that $^{100}\mathrm{Ru}$ can be interpreted as being a…
Quasi-particle and plasmaron properties in the electron gas
1972
The self-energy function of the degenerate electron gas is studied in an approximation which uses the dielectric function proposed by Singwi, Tosi, Land and Sjolander, and neglects the corresponding vertex corrections. Two contributions to the self-energy are distinguished which arise from the plasmon pole and the particle-hole continuum respectively. Comparison of the results is made with the analogous approximation to the self-energy which uses the RPA dielectric function, and with a further, simplified approximation. Subsequently the properties of the usual quasi-particle and of the plasmaron are calculated. Nummerically, the most significant effect found is a 25% reduction of the plasma…
Gamow-Teller decay of118Pd and of neighbouring even isotopes of palladium
1989
Neutron-rich isotopes of palladium were produced via the fission of238U by 20 MeV protons. These isotopes were selected using the ion guide-fed on-line mass-separator facility IGISOL at Jyvaskyla. Their decays were studied byβ-ray,γ-ray and conversion-electron spectroscopy. For114Pd and116Pd, the decay schemes established previously were confirmed; additionally multipolarities were determined for a few transitions. In the case of118Pd, only an approximate half-life was known from a previous radiochemical experiment. In the present study, 15 gamma transitions were observed, most of which were placed in a decay scheme. The half-life and the decay energy were found to beT1/2=1.9±0.1 s andQβ=4.…
AK=3two-quasiparticle isomer in98Sr
2002
The decay of on-line mass-separated ${}^{98}\mathrm{Rb}$ to ${}^{98}\mathrm{Sr}$ is studied by $\ensuremath{\gamma}$ spectroscopy. The revised decay scheme adds further evidence of the coexistence of very different shapes in ${}^{98}\mathrm{Sr}.$ A set of levels is proposed to originate from particle-hole pair excitations across the $Z=40$ spherical gap in analogy with ${}^{96}\mathrm{Sr}.$ A deformed $K=3$ band with probable even parity is built on a 7.1-ns isomer at 1838 keV. It is interpreted as a two-quasineutron excitation in accordance with a quantum Monte Carlo pairing calculation based on a deformed shell model. Configurations of the calculated lowest-lying two-quasiparticle levels …
Effects of orbital occupancies and spin–orbit partners on -decay rates
2010
Abstract Neutrinoless double beta ( 0 ν β β ) decay of the 76Ge, 82Se, 128Te, 130Te and 136Xe nuclei is discussed in terms of the associated nuclear matrix element (NME). The effects of the size of the single-particle model space and the occupancies of individual orbits on the NME are discussed by using the proton–neutron quasiparticle random-phase approximation (pnQRPA) with effective, G-matrix-derived nuclear forces. It is found that only in some cases the orbital occupancies play a decisive role for the size of the NME, whereas the inclusion of all the spin–orbit partners is essential to achieve a NME of reasonable quality. The obtained results are compared with published results of othe…
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) …