Modelling incomplete fusion dynamics of weakly-bound nuclei at near-barrier energies

The classical dynamical model for reactions induced by weakly-bound nuclei at near-barrier energies is developed further. It allows a quantitative study of the role and importance of incomplete fusion dynamics in asymptotic observables, such as the population of high-spin states in reaction products as well as the angular distribution of direct alpha-production. Model calculations indicate that incomplete fusion is an effective mechanism for populating high-spin states, and its contribution to the direct alpha production yield diminishes with decreasing energy towards the Coulomb barrier. It also becomes notably separated in angles from the contribution of no-capture breakup events. This should facilitate the experimental disentanglement of these competing reaction processes.Comment: 12 pages, 7 figures (for better resolution figures please contact the author), Accepted in Journal of Physics

Intruder bands and configuration mixing in the lead isotopes

A three-configuration mixing calculation is performed in the context of the interacting boson model with the aim to describe recently observed collective bands built on low-lying $0^+$ states in neutron-deficient lead isotopes. The configurations that are included correspond to the regular, spherical states as well as two-particle two-hole and four-particle four-hole excitations across the Z=82 shell gap.Comment: 20 pages, 4 figures, accepted by PRC, reference added for section 1 in this revised versio

Neutron-proton interaction in rare-earth nuclei: Role of tensor force

We investigate the role of the tensor force in the description of doubly odd deformed nuclei within the framework of the particle-rotor model. We study the rare-earth nuclei 174Lu, 180Ta, 182Ta, and 188Re using a finite-range interaction, with and without tensor terms. Attention is focused on the lowest K=0 and K=1 bands, where the effects of the residual neutron-proton interaction are particularly evident. Comparison of the calculated results with experimental data evidences the importance of the tensor-force effects.Comment: 8 pages, 5 figures, to be published on Physical Review

Measurement of conversion electrons with the 208Pb(p,n)208Bi^{208}Pb(p,n)^{208}Bi reaction and derivation of the shell model proton neutron hole interaction from the properties of 208Bi^{208}Bi

Conversion electrons from 208Bi have been measured using singles and coincidence techniques with the 208Pb(p,n)208Bi reaction at 9 MeV. The new information on multipolarities and spins complements that available from recent gamma-gamma-coincidence studies with the same reaction [Boutachkov et al., Nucl. Phys. A768, 22 (2006)]. The results on electromagnetic decays taken together with information on spectroscopic factors from earlier single-particle transfer reaction measurements represent an extensive data set on the properties of the one-proton one-neutron-hole states below 3 MeV, a spectrum which is virtually complete. Comparison of the experimental observables, namely, energies, spectroscopic factors, and gamma-branching ratios, with those calculated within the shell model allows extraction of the matrix elements of the shell model residual interaction. More than 100 diagonal and nondiagonal elements can be determined in this way, through a least squares fit to the experimental data. This adjustment of the interaction significantly affects the calculated properties of the gamma-ray transitions. Nevertheless, the matrix elements thus obtained are remarkably similar to those of a realistic interaction calculated from free-nucleon scattering. Characteristic features of the interaction are discussed

Octupole transitions in the 208Pb region

The 208Pb region is characterised by the existence of collective octupole states. Here we populated such states in 208Pb + 208Pb deep-inelastic reactions. γ-ray angular distribution measurements were used to infer the octupole character of several E3 transitions. The octupole character of the 2318 keV 17− → 14+ in 208Pb, 2485 keV 19/2 − → 13/2 + in 207Pb, 2419 keV 15/2 − → 9/2 + in 209Pb and 2465 keV 17/2 + → 11/2 − in 207Tl transitions was demonstrated for the first time. In addition, shell model calculations were performed using two different sets of two-body matrix elements. Their predictions were compared with emphasis on collective octupole states.This work is supported by the Science and Technology Facilities Council (STFC), UK, US Department of Energy, Office of Nuclear Physics, under Contract No. DEAC02-06CH11357 and DE-FG02-94ER40834, NSF grant PHY-1404442

Measured magnetic moments and shape coexistence in the neutron-deficient nuclei Pt-184,Pt-186,Pt-188

A novel implantation-decay technique has been employed to measure the magnetic moments of the 2(1)(+) states in the neutron-deficient nuclei Pt-184, Pt-186, and Pt-188. The magnetic moment systematics for the even Pt isotopes now extend from Pt-184(78)106 to Pt-198(78)120, spanning the upper half of the valence neutron shell. Despite the prolate-to-oblate shape transition near A = 190, they remain remarkably constant. The g(2(1)(+)) values for Pt-184,Pt-186,Pt-188 are consistent with shape-coexistence models in which the deformed configuration has a larger effective number of valence protons than the less-deformed configuration

Multiquasiparticle states in the neutron-rich nucleus 174 Tm

Deep inelastic and transfer reactions with an 820-MeV, 136Xe beam and various ytterbium and lutetium targets have been employed to study high-spin structures in the neutron-rich thulium isotopes beyond 171Tm. Results in the doubly odd nucleus, 174Tm, inc

Effect of oblate deformation on E3 strengths in light lead and polonium isotopes

The multipolarities of the main transitions deexciting yrast isomers in Pb-190 have been measured using conversion electron spectroscopy with pulsed beams. The enhanced E3 character of the 407 keV transition from the 11(-) isomer is confirmed and an independent value obtained for its lifetime. A new measurement of the properties of the 440 keV E3 decay from the corresponding 11(-) state in Pb-192, has resulted in the identification of a new branch and a significantly different lifetime from that reported previously. The abnormally large strength of the 11(-) to 8(+) transitions in both Pb-190 and Pb-192 match those known in some light polonium isotopes, an effect which is suggested to be linked to a change in structure of the orbitals in the 8(+) configuration when oblate deformation is established; the lowest Omega = 7/2(-) proton Nilsson orbital changes from being predominantly of h(9/2) character at sphericity to a mixed f(7/2)/h(9/2) parentage at oblate deformations, thus enabling an enhanced i(13/2) to f(7/2) octupole-coupled transition

Anomalous isomeric decays in 174Lu as a probe of K-mixing and interactions in deformed nuclei

A Kπ=13+, 280 ns four-quasiparticle isomer in the odd-odd nucleus 174Lu has been identified and characterized. The isomer decays to both Kπ=7+ and Kπ=0+ rotational bands obtained from the parallel and antiparallel coupling of the proton 7/2+[404] and neutron 7/2+[633] orbitals. K mixing caused by particle-rotation coupling explains the anomalously fast transition rates to the 7+ band but those to the 0+ band are caused by a chance degeneracy between the isomer and a collective state, allowing the mixing matrix element for a large K difference to be deduced

High-spin structure, K isomers, and state mixing in the neutron-rich isotopes 173 Tm and 175 Tm

High-spin states in the odd-proton thulium isotopes 173Tm and 175Tm have been studied using deep-inelastic reactions and γ-ray spectroscopy. In 173Tm, the low-lying structure has been confirmed and numerous new states have been identified, including a t