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The neutron-rich Ni isotopes have attracted attention in recent years because of the occurrence of shape or configuration coexistence. We report on the difference in population of excited final states in 70Ni following γ-ray tagged one-proton, one-neutron, and two-proton knockout from 71Cu, 71Ni, and 72Zn rare-isotope beams, respectively. Using variations observed in the relative transition intensities, signaling the changed population of specific final states in the different reactions, the role of neutron and proton configurations in excited states of 70Ni is probed schematically, with the goal of identifying those that carry, as leading configuration, proton excitations across the Z=28 shell closure. Such states are suggested in the literature to form a collective structure associated with prolate deformation. Adding to the body of knowledge for 70Ni, 29 new transitions are reported, of which 15 are placed in its level scheme. [ABSTRACT FROM AUTHOR]

A sequence of excited states has been established for the first time in the proton-rich nucleus 48Fe (Z=26, N=22). The technique of mirrored (i.e. analogue) one-nucleon knockout reactions was applied, in which the T z = ±2 mirror pair, 48Fe/48Ti were populated via one-neutron/one-proton knockout from the secondary beams 49Fe/49V, respectively. The analogue properties of the reactions were used to help establish the new level scheme of 48Fe. The inclusive and exclusive cross sections were determined for the populated states. Large differences between the cross sections for the two mirrored reactions were observed and have been interpreted in terms of different degrees of binding of the mirror nuclei and in the context of the recent observations of suppression of spectroscopic strength as a function of nuclear binding, for knockout reactions on light solid targets. Mirror energy differences (MED) have been determined between the analogue T = 2 states and compared with the shell model predictions. MED for this mirror pair, due to their location in the shell, are especially sensitive to excitations out of the f 7 / 2 shell, and present a stringent test of the shell-model prescription. [ABSTRACT FROM AUTHOR]

Proton capture on the excited isomeric state of 26Al strongly influences the abundance of 26Mg ejected in explosive astronomical events and, as such, plays a critical role in determining the initial content of radiogenic 26Al in presolar grains. This reaction also affects the temperature range for thermal equilibrium between the ground and isomeric levels. We present a novel technique, which exploits the isospin symmetry of the nuclear force, to address the long-standing challenge of determining proton-capture rates on excited nuclear levels. Such a technique has in-built tests that strongly support its veracity and, for the first time, we have experimentally constrained the strengths of resonances that dominate the astrophysical 26mAl(p,γ)27Si reaction. These constraints demonstrate that the rate is at least a factor ∼8 lower than previously expected, indicating an increase in the stellar production of 26Mg and a possible need to reinvestigate sensitivity studies involving the thermal equilibration of 26Al. [ABSTRACT FROM AUTHOR]

The structure of exotic nuclei provides valuable tests for state-of-the-art nuclear theory. In particular electromagnetic transition rates are more sensitive to aspects of nuclear forces and many-body physics than excitation energies alone. We report the first lifetime measurement of excited states in 21O, finding τ 1 / 2 + = 420 − 32 + 35 (stat) − 12 + 34 (sys) ps. This result together with the deduced level scheme and branching ratio of several γ -ray decays are compared to both phenomenological shell-model and ab initio calculations based on two- and three-nucleon forces derived from chiral effective field theory. We find that the electric quadrupole reduced transition probability of B (E 2 ; 1 / 2 + → 5 / 2 g. s. +) = 0.71 − 0.06 − 0.06 + 0.07 + 0.02 e2 fm4, derived from the lifetime of the 1 / 2 + state, is smaller than the phenomenological result where standard effective charges are employed, suggesting the need for modifications of the latter in neutron-rich oxygen isotopes. We compare this result to both large-space and valence-space ab initio calculations, and by using multiple input interactions we explore the sensitivity of this observable to underlying details of nuclear forces. [ABSTRACT FROM AUTHOR]

Angle-integrated cross-section measurements of the 56Ni(d , n) and (d , p) stripping reactions have been performed to determine the single-particle strengths of low-lying excited states in the mirror nuclei pair 57Cu−57Ni situated adjacent to the doubly magic nucleus 56Ni. The reactions were studied in inverse kinematics utilizing a beam of radioactive 56Ni ions in conjunction with the GRETINA γ -array. Spectroscopic factors are compared with new shell-model calculations using a full pf model space with the GPFX1A Hamiltonian for the isospin-conserving strong interaction plus Coulomb and charge-dependent Hamiltonians. These results were used to set new constraints on the 56Ni(p , γ)57Cu reaction rate for explosive burning conditions in x-ray bursts, where 56Ni represents a key waiting point in the astrophysical rp -process. [ABSTRACT FROM AUTHOR]

Excited states of the neutron-rich isotopes 42,44S and 41,43P have been studied via inverse-kinematics proton scattering from a liquid hydrogen target, using the GRETINA γ-ray tracking array to extract inelastic-scattering cross sections. Deformation lengths of the 21+ excitations in 42,44S have been determined and, when combined with deformation lengths determined with electromagnetic probes, yield the ratio of neutron-to-proton matrix elements Mn/Mp for the 21+ excitations in these nuclei. The present results for 41,43P(p,p') are used to compare two shell-model interactions, SDPF-U and SDPF-MU. As in a recent study of 42Si, the present results on 41,43P favor the SDPF-MU interaction. [ABSTRACT FROM AUTHOR]

We report on the observation of excited states in the neutron-deficient phosphorus isotopes 26,27,28P via in-beam γ-ray spectroscopy with both high-efficiency and high-resolution detector arrays. In 26P, a previously unobserved level has been identified at 244(3) keV, two new measurements of the astrophysically important 3/2+ resonance in 27P have been performed, γ decays have been assigned to the proton-unbound levels at 2216 and 2483 keV in 28P, and the γ-ray line-shape method has been used to make the first determination of the lifetimes of the two lowest-lying excited states in 28P. The expected Thomas-Ehrman shifts were calculated and applied to levels in the mirror nuclei. The resulting level energies from this procedure were then compared with the energies of known states in 26,27,28P. [ABSTRACT FROM AUTHOR]

We present a high-resolution in-beam γ-ray spectroscopy study of excited states in the mirror nuclei 55Co and 55Ni following one-nucleon knockout from a projectile beam of 56Ni. The newly determined partial cross sections and the γ-decay properties of excited states provide a test of state-of-the-art nuclear structure models and probe mirror symmetry in unique ways. The new experimental data are compared to large-scale shell-model calculations in the full pf space which include charge-dependent contributions. A mirror asymmetry for the partial cross sections leading to the two lowest 3/2- states in the A=55 mirror pair was identified as well as a significant difference in the E1 decays from the 1/2+1 state to the same two 3/2- states. The mirror asymmetry in the partial cross sections cannot be reconciled with the present shell-model picture or small mixing introduced in a two-state model. The observed mirror asymmetry in the E1 decay pattern, however, points at stronger mixing between the two lowest 3/2- states in 55Co than in its mirror 55Ni. [ABSTRACT FROM AUTHOR]

Excited states in the neutron-rich 70Fe nucleus were populated in a one-proton removal reaction from 71Co projectiles at 87 MeV/nucleon. A new transition was observed with the γ-ray tracking array GRETINA and shown to feed the previously assigned 4+1 state. In comparison to reaction theory calculations with shell-model spectroscopic factors, it is argued that the new γ ray possibly originates from the 6+1 state. It is further shown that the Doppler-reconstructed γ-ray spectra are sensitive to the very different lifetimes of the 2+ and 4+ states, enabling their approximate measurement. The emerging structure of 70Fe is discussed in comparison to LNPS-new large-scale shell-model calculations. [ABSTRACT FROM AUTHOR]

Lifetime measurements of excited states in the neutron-rich nucleus 43S were performed by applying the recoil-distance method on fast rare-isotope beams in conjunction with the Gamma-Ray Energy Tracking In-beam Nuclear Array. The new data based on γγ coincidences and lifetime measurements resolve a doublet of (3/2-) and (5/2-) states at low excitation energies. Results were compared to the π(sd)-ν(pf) shell model and antisymmetrized molecular dynamics calculations. The consistency with the theoretical calculations identifies a possible appearance of three coexisting bands near the ground state of 43S: the Kπ=1/2- band built on a prolate-deformed ground state, a band built on an isomer with a 1f-17/2 character, and a suggested excited band built on a newly discovered doublet state. The latter further confirms the collapse of the N=28 shell closure in the neutron-rich region. [ABSTRACT FROM AUTHOR]