Properties Of Low-lying Collective States Research Articles

Theoretical Calculation of the IBM1 Parameters and Band Crossing in Even Cerium Isotopes

An extended microscopic version of the interacting-boson model is developed. The properties of yrast-band states in even cerium isotopes up to the spin–parity of $$I^{\pi}=18^{+}$$ are calculated on the basis of this model. These spin values include those at which band crossing occurs. The model parameters are calculated on the basis of employing an average spherical potential and residual multipole forces. An extension of the model is accomplished via taking into account high-spin quasiparticle pairs, whereby a satisfactory description of energies and $$B(E\text{2})$$ values was obtained without introducing effective charges. The present investigation is a continuation of a similar analysis of the properties of low-lying collective states in even xenon and barium isotopes.

Excited states of odd-mass nuclei with different deformation-dependent mass coefficients

Experimental data indicate that the mass tensor of collective Bohr Hamiltonian cannot be considered as a constant but should be considered as a function of the collective coordinates. In this work our purpose is to investigate the properties of low-lying collective states of the odd nuclei $^{173}$Yb and $^{163}$Dy by using a new generalized version of the collective quadrupole Bohr Hamiltonian with deformation-dependent mass coefficients. The proposed new version of the Bohr Hamiltonian is solved for Davidson potential in $\beta$ shape variable, while the $\gamma$ potential is taken to be equal to the harmonic oscillator. The obtained results of the excitation energies and B(E2) reduced transition probabilities show an overall agreement with the experimental data. Moreover, we investigate the effect of the deformation dependent mass parameter on energy spectra and transition rates in both cases, namely: when the mass coefficients are different and when they are equal. Besides, we will show the positive effect of the present formalism on the moment of inertia.

Local suppression of collectivity in theN=80isotones at theZ=58subshell closure

Background: Recent data on N=80 isotones have suggested that the proton π(1g7/2) subshell closure at Z=58 has an impact on the properties of low-lying collective states. Purpose: Knowledge of the B(E2;21+→01+) value of 140Nd is needed in order to test this conjecture. Method: The unstable, neutron-rich nucleus 140Nd was investigated via projectile Coulomb excitation at the REX-ISOLDE facility with the MINIBALL spectrometer. Results: The B(E2) value of 33(2) W.u. expands the N=80 systematics beyond the Z=58 subshell closure. Conclusions: The measurement demonstrates that the reduced collectivity of 138Ce is a local effect possibly due to the Z=58 subshell closure and requests refined theoretical calculations. The latter predict a smoothly increasing trend.Received 28 March 2013DOI:https://doi.org/10.1103/PhysRevC.88.021302©2013 American Physical Society

Microscopic calculation of interacting boson model parameters by potential-energy surface mapping

A coherent state technique is used to generate an interacting boson model (IBM) Hamiltonian energy surface which is adjusted to match a mean-field energy surface. This technique allows the calculation of IBM Hamiltonian parameters, prediction of properties of low-lying collective states, as well as the generation of probability distributions of various shapes in the ground state of transitional nuclei, the last two of which are of astrophysical interest. The results for krypton, molybdenum, palladium, cadmium, gadolinium, dysprosium, and erbium nuclei are compared with experiment.

On the Q n −Q p deformation energy surfaces of neutron-rich oxygen isotopes

We present an analysis based on the generator coordinate method that allows one to disentangle the neutron and proton contributions to the properties of low-lying collective states in oxygen isotopes.

Decay properties of low-lying collective states in 132Ba

The decay properties of low-lying collective states in 132Ba were studied by means of γ spectroscopy following the β-decay of the 2 − ground state ( T 1/2=4.8 h) and a 6 − isomer ( T 1/2=24.3 min) of 132La. The lanthanum nuclei were produced at the Cologne fn tandem accelerator using the reaction 122Sn( 14N, 4n) 132La. The γγ coincidences and singles spectra were measured with the osiris-cube spectrometer. Beside ground and quasi-gamma band many other low-lying states were observed. The γγ angular correlations were analyzed to assign spins to the excited states, and to determine the multipolarities of the depopulating the γ transitions. We also confirmed the expected dominant E2 character of transitions in the quasi-gamma band and from the quasi-gamma to the ground band but with a certain deviation: the decay 6 + 2→6 + 1 shows an unexpected large M1 fraction. Also the decays of the third, fourth and fifth 2 + states are dominated by M1 radiation. A level at 1660 keV could be identified as the 0 + 3 state in 132Ba. The experimental data are compared with calculations using the proton–neutron interacting boson model (IBM-2). Good agreement is reached in the vicinity of the O(6) limit.

Chaotic properties of the interacting boson model

We study classically and quantum mechanically the chaotic properties of low-lying collective states of nuclei by using the interacting boson model. Classical and quantal diagrams are constructed for several measures of chaos in a general parameter space of the hamiltonian known as Casten's triangle. Strong correlations are found between the classical and quantal results. A new nearly regular region is discovered.

Collective shape transition in the low-lying spectra of nuclei nearN=28region

Deformed configuration mixing shell model calculations for the energy spectra and electromagnetic properties of low-lying collective states of $^{51}\mathrm{Cr}$, $^{53}\mathrm{Fe}$, $^{50}\mathrm{Ti}$, $^{52}\mathrm{Cr}$, $^{54}\mathrm{Fe}$, $^{53}\mathrm{Cr}$, and $^{55}\mathrm{Fe}$ have been performed. For each of these nuclei these calculations give rise to a highly deformed band when a neutron is promoted from the predominantly ${({f}_{\frac{7}{2}})}^{n}$ spherical ground intrinsic configuration to the unoccupied ($\mathrm{pf}$) orbits. The ${K}^{\ensuremath{\pi}}$ values of these excited bands are $\frac{1}{{2}^{\ensuremath{-}}}$, ${4}^{+}$, and $\frac{7}{{2}^{\ensuremath{-}}}$ for the nuclei having $N=27, 28, \mathrm{and} 29$, respectively. The energy spectra and electromagnetic properties of these calculated excited bands are compared with those experimentally observed. Following high-spin members of the collective bands have been predicted by the calculations: $J=\frac{11}{2}, \frac{13}{2}, \frac{15}{2}, \frac{17}{2}, \mathrm{and} \frac{19}{2}$ levels at 2.7, 3.8, 4.36, 5.94, and 6.47 MeV, respectively, in $^{51}\mathrm{Cr}$, $J=\frac{9}{2}, \frac{11}{2}, \frac{13}{2}, \frac{15}{2}, \mathrm{and} \frac{17}{2}$ levels at 2.94, 3.67, 4.95, 6.01, and 7.47 MeV, respectively, in $^{53}\mathrm{Fe}$, $J=\frac{15}{2}, \frac{17}{2}, \frac{19}{2}, \mathrm{and} \frac{21}{2}$ levels at 4.65, 5.77, 7.04, and 8.41 MeV, respectively, in $^{53}\mathrm{Cr}$, and $J=\frac{15}{2}, \frac{17}{2}, \mathrm{and} \frac{19}{2}$ levels at 5.53, 6.92, and 8.33 MeV, respectively, in $^{55}\mathrm{Fe}$. In $^{50}\mathrm{Ti}$, $^{52}\mathrm{Cr}$, and $^{54}\mathrm{Fe}$ the present model suggests an interesting possibility of $K={3}^{+}$ collective band lying close in energy to the recently observed $K={4}^{+}$ collective bands.NUCLEAR STRUCTURE $^{50}\mathrm{Ti}$, $^{51,52,53}\mathrm{Cr}$, and $^{53,54,55}\mathrm{Fe}$. Calculated spectra, $B(E2)$ and $B(M1)$ transition strengths, $\frac{E2}{M1}$ mixing ratios, branching ratios and lifetimes in deformed configuration mixing shell model formalism in ${(\mathrm{fp})}^{n}$ model space. Modified Kuo-Brown interaction. Comparison with experiment and shell model and Nilsson model calculations.