Shift of the 21+^+_1 state of 10^{10}Be in the ternary cold fission of 252^{252}Cf

Recent experimental data indicate that in the ternary cold fission of $^{252}$Cf the energy of the first excited state of the accompanying light cluster $^{10}$Be is decreased by an amount ranging between $\approx$ 6 and 26 keV. A model is proposed to calculate the shift of the vibrational 2$^+_1$ state in $^{10}$Be when its heavy companions are the even-even nuclei $^{146}$Ba and $^{96}$Sr. The stiffness parameters of the $\beta$-vibrations are calculated within the self-consistent Hartree-Fock method with BCS pairing correlations taken into account, and its change is determined by the interaction of the light cluster with the heavy fragments. The results are pointing to a dependence of the shift magnitude and signature on the relative distance between the three clusters and their mutual orientation. Eventually it is the anharmonic perturbation of the spherical vibrator which is responsible for obtaining a negative energy shift of the 2$^+_1$ state.Comment: 4 pages, 3 figure

Role of Fragment Higher Static Deformations in the Cold Binary Fission of 252^{252}Cf

We study the binary cold fission of $^{252}$Cf in the frame of a cluster model where the fragments are born to their respective ground states and interact via a double-folded potential with deformation effects taken into account up to multipolarity $\lambda=4$. The preformation factors were neglected. In the case when the fragments are assumed to be spherical or with ground state quadrupole deformation, the $Q$-value principle dictates the occurence of a narrow region around the double magic $^{132}$Sn, like in the case of cluster radioactivity. When the hexadecupole deformation is turned on, an entire mass-region of cold fission in the range 138 - 156 for the heavy fragment arise, in agreement with the experimental observations. This fact suggests that in the above mentioned mass-region, contrary to the usual cluster radioactivity where the daughter nucleus is always a neutron/proton (or both) closed shell or nearly closed shell spherical nucleus, the clusterization mechanism seems to be strongly influenced by the hexadecupole deformations rather than the $Q$-value.Comment: 10 pages, 12 figure

IBM-1 description of the fission products 108,110,112^{108,110,112}Ru

IBM-1} calculations for the fission products $^{108,110,112}$Ru have been carried out. The even-even isotopes of Ru can be described as transitional nuclei situated between the U(5) (spherical vibrator) and SO(6) ($\gamma$-unstable rotor) symmetries of the Interacting Boson Model. At first, a Hamiltonian with only one- and two-body terms has been used. Excitation energies and $B$(E2) ratios of gamma transitions have been calculated. A satisfactory agreement has been obtained, with the exception of the odd-even staggering in the quasi-$\gamma$ bands of $^{110,112}$Ru. The observed pattern is rather similar to the one for a rigid triaxial rotor. A calculation based on a Hamiltonian with three-body terms was able to remove this discrepancy. The relation between the IBM and the triaxial rotor model was also examined.Comment: 22 pages, 8 figure

Phase transitions above the yrast line in 154Dy

Spectra of the E2 quasicontinuum γ rays feeding different spin regions of the 154Dy yrast line have been extracted. These are compared with corresponding theoretical spectra obtained by numerical simulations based on temperature-dependent Hartree-Fock theory, with thermal shape fluctuations. In this manner, different regions of the spin-energy plane can be examined. The results support the predictions of a smeared-out phase transition at high spin above the yrast line

Superdeformed band in Dy154

A superdeformed band has been found in the Dy154 (N=88) nucleus. The dynamic moment of inertia is identical to that of the yrast superdeformed band of Dy152 and the transition energies are similar to those of an excited superdeformed band in Dy153. It is proposed that the two valence neutrons above the N=86 shell gap occupy the deformation-driving [514]9/2 orbital

Competition between terminating and collective structures above spin 40ℏ in 154Dy

High-spin states in 154Dy were studied with the Gammasphere spectrometer using the 36S(122Sn,4n) reaction. Band terminating states were identified in the spin range I= (36-48)ℏ, and were found to compete with collective rotational cascades up to the highest observed spins. Several "sidebands" feeding the terminating structures were identified as well. A band dominated by M1 transitions was observed to terminate at Iπ = 42-. The data are interpreted within the framework of configuration-dependent cranked Nilsson-Strutinsky calculations without pairing

Excited states in 176, 178Hg and shape coexistence in very neutron-deficient Hg isotopes

Excited states have been observed for the first time in the neutron-deficient 176,178Hg nuclei using the recoil-decay tagging (RDT) technique in which prompt γ rays are associated with a particular isotope through a correlation with the characteristic ground state α decay. Below N = 102, the excitation energy of a rotational band built on a prolate shape (β2 ∼ 0.25) increases with decreasing mass to the point where there is no longer any evidence for its presence at low spin in 176Hg. The data are in qualitative agreement with recent mean field calculations

5He ternary fission yields of 252Cf and 235U(n,f)

The relative 4He and 5He ternary fission yields were determined from a careful analysis of the energy distribution of α spectra from a new measurement with a 252Cf source and from published data on 252Cf and 235U(n,f). The kinetic energies of the 5He and 4He ternary particles were found to be approximately 11 and 16 MeV, respectively. 5He particles contribute 10-20% to the total alpha yield with the remainder originating from 4He accompanied fission

Identification of 181Hg and shape coexistence in odd-A Hg isotopes

In-beam γ-ray transitions in 181Hg, the lightest odd-A Hg isotope known thus far, have been identified from fragment mass-γ and γ-γ coincidence measurements. Five prolate deformed rotational bands were placed in the level scheme. A decoupled band built on the strongly prolate deformed 1/2-[521] ground state was observed up to 29/2-. A 5/2-[512] configuration is suggested for a pair of strongly coupled bands displaying no signature splitting. The other two bands are also signature partner bands. They are populated with the largest intensity and exhibit splitting. They have been associated with the mixed neutron i13/2 orbitals and are proposed to decay to an i13/2 isomeric state associated with an oblate state

γ -soft Ba 146 and the role of nonaxial shapes at N≈90

Low-spin states in the neutron-rich, N=90 nuclide Ba146 were populated following β decay of Cs146, with the goal of clarifying the development of deformation in barium isotopes through delineation of their nonyrast structures. Fission fragments of Cs146 were extracted from a 1.7-Ci Cf252 source and mass selected using the CAlifornium Rare Ion Breeder Upgrade (CARIBU) facility. Low-energy ions were deposited at the center of a box of thin β detectors, surrounded by a highly efficient high-purity Ge array. The new Ba146 decay scheme now contains 31 excited levels extending up to ∼2.5 MeV excitation energy, double what was previously known. These data are compared to predictions from the interacting boson approximation (IBA) model. It appears that the abrupt shape change found at N=90 in Sm and Gd is much more gradual in Ba and Ce, due to an enhanced role of the γ degree of freedom