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We discuss a phenomenological shell model analysis of the structure of 48 , 49 , 50 Ca. Based on simple arguments, we propose wavefunctions fit to the available data on spectroscopic factors derived from direct one neutron addition and removal reactions. These empirical wavefunctions are then used to calculate properties of low-lying states in 49 , 50 , 51 Ca, which are consistent with available experimental data. Our analysis appears to capture the main ingredients at play in the low-lying properties of these nuclei and emphasize the prominent role of pairing correlations. We also present predictions that could motivate further work. [ABSTRACT FROM AUTHOR]

While the phenomenon of one- and two-neutron ground-state halo nuclei is well established, the effects of weak binding on nuclear excitation properties remain largely unexplored. Motivated by this question and by recent data in 40 Mg we investigate the coupling of weakly bound (halo) valence neutrons to a core using the known properties of 40 Mg to explore and illustrate possible particle-core coupling schemes and their impact on the low-lying excitation spectrum. [ABSTRACT FROM AUTHOR]

We present expressions for the matrix elements of the spin–spin operator S n · S p in a variety of coupling schemes. These results are then applied to calculate the expectation value ⟨ S n · S p ⟩ in eigenstates of a schematic Hamiltonian describing neutrons and protons interacting in a single-l shell through a Surface Delta Interaction. The model allows us to trace ⟨ S n · S p ⟩ as a function of the competition between the isovector and isoscalar interaction strengths and the spin–orbit splitting of the j = l ± 1 / 2 shells. We find negative ⟨ S n · S p ⟩ values in the ground state of all even–even N = Z nuclei, contrary to what has been observed in hadronic inelastic scattering at medium energies. We discuss the possible origin of this discrepancy and indicate directions for future theoretical and experimental studies related to neutron–proton spin–spin correlations. [ABSTRACT FROM AUTHOR]

With new experimental information on nuclei far from stability being available, a systematic investigation of excitation energies and electromagnetic properties along the N = 10 , 11 , 12 isotones and Z = 10 , 11 , 12 isotopes is presented. The experimental data are discussed in the context of the appearance and disappearance of shell closures at N = Z = 8 , 14 , 16 , 20 , and compared to an effective-interaction approach applied to neutrons and protons in d 5 / 2 2 , 3 , 4 configurations. In spite of its simplicity the model is able to explain the observed properties. [ABSTRACT FROM AUTHOR]

In this contribution, we present recent results related to the quadrupole collectivity in neutron rich carbon isotopes. B(E2) transitions strengths derived from lifetime measurements are interpreted in a seniority scheme, indicating an increase role of proton excitations due to the reduction of the p3/2-p½ spin-orbit splitting. We also discuss the evolution of the N = 40 shell closure with isospin and report on preliminary results of Coulomb Excitation experiments on 66;68Fe and 64Cr. Finally, a short review of the gamma-ray tracking technique and a status report of GRETINA are presented. Some aspects of the exciting physics campaign being carried out at NSCL/MSU are discussed. [ABSTRACT FROM AUTHOR]

Three low-lying 8+ states have been identified in 192Pb . A newly observed cascade of $ \gamma$ -rays built directly on the 8+ 1 state is compared to the previously identified, weakly rotational band above the 11- $ \pi$ i13/2 , h9/2 isomer in the same nucleus, and to analogous structures in 194Pb . The similarity of all four structures lends support to the suggestion that the 8+ 1 configurations are of a similar oblate deformation to the 11- isomers. The excitation energies of all three 8+ states in 192Pb and 190Pb are compared to systematics. The possibility that one of the 8+ states in 192Pb is associated with a prolate shape is discounted. [ABSTRACT FROM AUTHOR]

A superdeformed band has been observed in theN= 108 isotope190Pb. This is the most neutron-deficient Pb isotope in which superdeformed states have been observed. Several theoretical approaches have predicted thatN= 108 will mark the limit of observable superdeformation in the Pb isotopes. The band, which consists of five (possibly six) transitions, is observed to feed at least one isomeric level in its decay to the ground state. This decay pattern supports a spin assignment of 10? for the lowest observed level. [ABSTRACT FROM AUTHOR]

It is pointed out that the ground state of n neutrons and n protons in a single-j shell, interacting through an isoscalar (T=0) pairing force, is not paired, J=0, but rather spin aligned, J=n. This observation is explained in the context of a model of isoscalar P (J=1) pairs, which is mapped onto a system of p bosons, leading to an approximate analytic solution of the isoscalar-pairing limit in jj coupling. [ABSTRACT FROM AUTHOR]

The apparent splitting between orbitals that are spin-orbit partners can be substantially influenced by the effects of weak binding. In particular, such effects can account for the observed decrease in separation of the neutron 1p3/2 and 1p1/2 orbitals between the 41Ca and 35Si isotopes. This behavior has been the subject of recent experimental and theoretical works and cited as evidence for a proton "bubble" in 34Si causing an explicit weakening of the spin-orbit interaction. The results reported here suggest that the change in the separation between the 1p3/2 and 1p1/2 partners occurs dominantly because of the behavior of the energies of these 1p neutron states near zero binding. [ABSTRACT FROM AUTHOR]

There is significant evidence supporting the existence of deformed ground states within the neutron-rich N≈20 neon, sodium, and magnesium isotopes that make up what is commonly called the "island of inversion." However, the rotational band structures, which are a characteristic fingerprint of a rigid nonspherical shape, have yet to be observed. In this work, we report on a measurement and analysis of the yrast (lowest lying) rotational band in 32Mg up to spin I=6+ produced in a two-step projectile fragmentation reaction and observed using the state-of-the-art γ-ray tracking detector array, GRETINA (γ-ray energy tracking in-beam nuclear array). Large-scale shell-model calculations using the SDPF-U-MIX effective interaction show excellent agreement with the new data. Moreover, a theoretical analysis of the spectrum of rotational states as a function of the pairing gap, together with cranked-shell-model calculations, provides intriguing evidence for a reduction in pairing correlations with increased angular momentum, also in line with the shell-model results. [ABSTRACT FROM AUTHOR]

The first lifetime measurement used to study the magnetic response of halo nuclei is presented. The lifetime of the first excited state of the one-neutron halo nucleus 19C has been measured by two complementary Doppler-shift techniques with the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA). The B(M 1 ; 3/2+ →1/2g,s+) strength of 3.21(25)x 10-3µ²N determined for this decay represents a strongly hindered M1 transition among light nuclei. Shell-model calculations predict a strong hindrance due to the near-degeneracy of the S1/2 and d5/2 orbitals among neutron-rich carbon isotopes, while tensor corrections and loosely bound effects are necessary to account for the remaining strength. [ABSTRACT FROM AUTHOR]

Intermediate-energy Coulomb excitation measurements are performed on the N ≥ 40 neutron-rich nuclei 66,68Fe and 64Cr. The reduced transition matrix elements providing a direct measure of the quadrupole collectivity B(E2;21+ → 01+) are determined for the first time in 68Fe42 and 64Cr40 and confirm a previous recoil distance method lifetime measurement in 66Fe40. The results are compared to state-of-the-art large-scale shell-model calculations within the full fpgd neutron orbital model space using the Lenzi-Nowacki-Poves-Sieja effective interaction and confirm the results of the calculations that show these nuclei are well deformed. [ABSTRACT FROM AUTHOR]

Excited states in the neutron-rich isotopes 33P and 34P were populated by the 18O+18O fusion-evaporation reaction at Elab=24 MeV. The Gammasphere array was used along with the Microball particle detector array to detect γ transitions in coincidence with the charged particles emitted from the compound nucleus 36S. The use of Microball enabled the selection of the proton emission channel. It also helped in determining the exact position and energy of the emitted proton; this was later employed in kinematic Doppler corrections. 16 new transitions and 13 new states were observed in 33P and 21 γ rays and 20 energy levels were observed in 34P for the first time. The nearly 4π geometry of Gammasphere allowed the measurement of γ-ray angular distributions leading to spin assignments for many states. The experimental observations for both isotopes were interpreted with the help of shell-model calculations using the (0+1)ℏω PSDPF interaction. The calculations accounted for both the 0p-0h and 1p-1h states reasonably well and indicated that 2p-2h excitations might dominate the higher-spin configurations in both 33P and 34P. [ABSTRACT FROM AUTHOR]