Search results for "quasiparticle"
showing 10 items of 280 documents
Identification of theKπ=8−rotational band in138Gd
1998
A ${K}^{\ensuremath{\pi}}{=8}^{\ensuremath{-}}$ collective rotational band has been established upon the 6 $\ensuremath{\mu}$s isomeric state in the very neutron-deficient nucleus ${}^{138}\mathrm{Gd}.$ The band was observed using a technique involving the correlation of $\ensuremath{\gamma}$-ray transitions across the isomeric state. The single-particle configuration of the isomer has been deduced from the $\ensuremath{\Delta}I=2$ to $\ensuremath{\Delta}I=1$ intensity branching ratios. In addition, a series of other $\ensuremath{\gamma}$-ray transitions were observed which are reasoned to be part of a higher-lying four quasiparticle structure which decays through the ${K}^{\ensuremath{\pi}…
Pronounced shape change induced by quasiparticle alignment
2000
Mean lifetimes of high-spin states of Kr-74 have been determined using the Doppler-shift attenuation method. The high-spin states were studied using the Ca-40(Ca-40, alpha 2p) reaction at a beam energy of 160 MeV with the GASP gamma-ray spectrometer. The ground-state band and negative parity side band show the presence of three different configurations in terms of transitional quadrupole deformations. A dramatic shape change was found along the ground-state band after the S-band crossing. The deduced quadrupole deformation changes are well reproduced by cranked Woods-Saxon Strutinsky calculations.
Experimental evidence for chirality in the odd-A 105Rh
2004
Abstract High-spin states in 105 Rh were populated by the 96 Zr( 13 C, p3n) reaction at beam energies of 51 and 58 MeV, and studied using the EUROBALL IV γ -ray spectrometer and the DIAMANT charged particle array. A pair of nearly degenerate Δ I = 1 three-quasiparticle bands with the same spins and parity have been observed. Comparison of the experimental results with tilted axis cranking calculations confirms the chiral character of the two bands, while arguments based on the excitation of particles within the π g 9 / 2 ν ( h 11 / 2 ) 2 configuration of the yrast band and comparison with the previously observed γ band exclude the other possible interpretations. This is the first experiment…
Strength ofJπ=1+Gamow-Teller and isovector spin monopole transitions in double-β-decay triplets
2014
In this work we study systematically the energetics and intensity distributions of Gamow-Teller (GT${}^{\ifmmode\pm\else\textpm\fi{}}$) and isovector spin monopole (IVSM${}^{\ifmmode\pm\else\textpm\fi{}}$) transitions from the ground states of the pairs ($^{76}\mathrm{Ge}$,$^{76}\mathrm{Se}$), ($^{82}\mathrm{Se}$,$^{82}\mathrm{Kr}$), ($^{100}\mathrm{Mo}$,$^{100}\mathrm{Ru}$), ($^{116}\mathrm{Cd}$,$^{116}\mathrm{Sn}$), ($^{128}\mathrm{Te}$,$^{128}\mathrm{Xe}$), ($^{130}\mathrm{Te}$,$^{130}\mathrm{Xe}$), and ($^{136}\mathrm{Xe}$,$^{136}\mathrm{Ba}$), of double-beta-decay initial and final nuclei, to the ${J}^{\ensuremath{\pi}}={1}^{+}$ excited states of the intermediate odd-odd nuclei $^{76}\…
Collective excitations in the transitional nucleiRe163andRe165
2015
Excited states in the neutron-deficient nuclei ${}_{75}^{163}{\mathrm{Re}}_{88}$ and ${}_{75}^{165}{\mathrm{Re}}_{90}$ were populated in the ${}^{106}{\mathrm{Cd}(}^{60}\mathrm{Ni},\phantom{\rule{0.16em}{0ex}}p2n\ensuremath{\gamma})$ and ${}^{92}{\mathrm{Mo}(}^{78}\mathrm{Kr}$, $3p2n\ensuremath{\gamma})$ fusion-evaporation reactions at bombarding energies of 270 and 380 MeV, respectively. \ensuremath{\gamma} rays were detected at the target position using the JUROGAM spectrometer while recoiling ions were separated in-flight by the RITU gas-filled recoil separator and implanted in the GREAT spectrometer. The energy level schemes for $^{163}\mathrm{Re}$ and $^{165}\mathrm{Re}$ were identifie…
Lipkin method of particle-number restoration to higher orders
2014
Background: On the mean-field level, pairing correlations are incorporated through the Bogoliubov-Valatin transformation, whereupon the particle degrees of freedom are replaced by quasiparticles. This approach leads to a spontaneous breaking of the particle-number symmetry and mixing of states with different particle numbers. In order to restore the particle number, various methods have been employed, which are based on projection approaches before or after variation. Approximate variation-after-projection (VAP) schemes, utilizing the Lipkin method, have mostly been used within the Lipkin-Nogami prescription. Purpose: Without recurring to the Lipkin-Nogami prescription, and using instead st…
Systematic study of the single-state dominance in 2νββ decay transitions
1999
Abstract The single-state-dominance hypothesis (SSDH) states that the decay rates of the two-neutrino double-beta decay are governed by a virtual two-step transition connecting the initial and final ground states through the first 1 + state, 1 l + , of the intermediate odd-odd nucleus, for those odd-odd nuclei where the 1 l + state is the ground state. To investigate the validity of the SSDH we have performed a systematical theoretical analysis of all known double-beta-decay transitions where the SSDH conditions are fulfilled. the calculations are based on the quasiparticle random-phase approximation (QRPA) and the results have been obtained by using realistic single-particle bases and real…
Systematics of the α-decay to rotational states
2006
We analyze \ensuremath{\alpha} decays to rotational states in even-even nuclei by using the stationary coupled channels approach. Collective excitations are described by the rigid rotator model. The \ensuremath{\alpha}-nucleus interaction is given by a double folding procedure using M3Y plus Coulomb nucleon-nucleon forces. We use a harmonic oscillator repulsive potential with one independent parameter, to simulate the Pauli principle. The decaying state is identified with the first resonance inside the resulting pocketlike potential. The energy of the resonant state is adjusted to the experimental Q value by using the depth of the repulsion. We obtained a good agreement with existing experi…
Folding description of the fine structure of α decay to2+vibrational and transitional states
2007
We analyze \ensuremath{\alpha}-decays to ground and ${2}^{+}$ vibrational states in even-even nuclei by using a coupled channels formalism. The \ensuremath{\alpha}-nucleus interaction is simulated by a double folding procedure using M3Y plus Coulomb two-body forces. Collective excitations are described by vibrations of the nuclear surface. We use a repulsive potential, with one independent parameter, in order to simulate Pauli principle and to adjust the energy of the resonant state to the experimental $Q$-value. The decaying state is identified with the zero nodes resonance inside the resulting pocket-like potential. We have found that the fine structure is very sensitive to the strength o…
Study of the low-lying collective states in 94–100Mo isotopes using the MAVA
2006
Abstract A systematic investigation of reduced electric quadrupole decay strengths, B ( E 2 ) and level energies of even 94–100 Mo isotopes is performed using the microscopic anharmonic vibrator approach (MAVA). The MAVA is suited for dynamical microscopic description of two-phonon-like states and their energy splitting due to interaction with low-lying one-phonon states. The starting point for the model is a realistic single-particle valence space and a microscopic many-body Hamiltonian which is used to generate the one-phonon states by the use of the quasiparticle random-phase approximation (QRPA). The same Hamiltonian generates also the interaction between the one- and two-phonon states.…