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Nuclei far from the line of stability are a focal point of contemporary nuclear physics. Nuclear structure studies along the proton dripline remain an important component of the scientific program at the ATLAS facility. The Gammasphere gamma-ray array and the Fragment Mass Analyzer offer the unprecedented sensitivity and selectivity required to study nuclei at and beyond the proton dripline. Recent results in proton decay studies, in-beam γ-ray spectroscopy around 100Sn and studies of proton resonances in light nuclei involved in the astrophysical hydrogen burning are presented. Future prospects in the context of planned and on-going upgrades of ATLAS and experimental apparatus are also briefly discussed. [ABSTRACT FROM AUTHOR]

This work focus on the electromagnetic decay properties of the heaviest known mirror pair 67As and 67Se, produced in the fusion evaporation reaction 32S+40Ca, with a E = 90 MeV beam provided by the ATLAS accelerator at Argonne National Laboratory. The high selectivity required to investigate these proton-rich nuclei was achieved with the concurrent employment of Gammasphere, Neutron-Shell, and Microball. The full array allowed to obtain the level scheme of the 67Se nucleus up to 5.56 MeV, and 5 new transitions were assigned to the known 67As level-scheme. The level spin and parities were assigned using the ADO analysis and symmetry arguments. [ABSTRACT FROM AUTHOR]

The 12C(16O,γ)28Si radiative capture reaction has been studied at energies close to the Coulomb barrier at Triumf (Vancouver) using the Dragon spectrometer and its associated BGO array. It has been observed that the γ decay flux proceeds mainly via states around 10–11 MeV and via the direct feeding of the 28Si 31- (6879 keV) and 42+ (6888 keV) deformed states. A discussion is presented about this selective feeding as well as perspectives for the use of novel detection systems for the study of light heavy-ion radiative capture reactions. [ABSTRACT FROM AUTHOR]

Classical novae are a site of explosive nucleosynthesis where hydrogen rich material from a companion giant star accretes onto the surface of a white warf. Critical to our understanding of nova explosions are proton-capture reaction rates involved in the nucleosynthesis. While, ideally, all of the relevant (p,γ) reactions would be measured directly, in practice, such measurements are very challenging and are only possible in a few cases. This provides considerable scope for indirect measurements including transfer reactions, mass measurements, beta-decay and gamma-ray spectroscopy. The latter technique, until recently largely neglected as an input in nuclear astrophysics analyses, has clear advantages in locating resonances with high energy precision and assisting in determining the spin and parity of resonances. Such information is very valuable in a complementary approach to indirect determinations of key reaction rates. [ABSTRACT FROM AUTHOR]

Coulomb excitation experiments in inverse kinematics on beams of stable 134,132,130,128,126,124Xe ions impinging on a carbon target at energies of 82% of the respective Coulomb barriers have been performed. The one-phonon 21,ms+ states have been tracked and identified in 134,132,130,128Xe from the 2i,ms+→21+ M1 strength distributions and from 01+→2i,ms+ E2 strength distributions responsible for the one-step Coulomb excitation processes. The evolution of the one-phonon 21,ms+ state within the seven even-even stable Xe isotopes is here presented. [ABSTRACT FROM AUTHOR]

Excited states in 124Xe have been studied via the 12C(124Xe,124Xe*) Coulomb excitation reaction. Relative cross-sections have been determined from the γ-ray yields observed with Gammasphere. The E2 strengths between the low-spin states in 124Xe have been determined. The results clearly show the realization of the O(5) symmetry even for the off-yrast states with high τ, while the O(6) symmetry seems to be already broken. [ABSTRACT FROM AUTHOR]

The identification of single-particle states in heavy actinide nuclei by means of studying their decay schemes plays a seminal role in understanding the structure of the heaviest elements and testing the predictive power of modern theoretical models. The heaviest odd-mass nuclides available in sufficient quantity for detailed decay spectroscopic studies are 20-h 255 Fm (for neutrons) and 20-d 253Es (for protons). Decay spectra of these isotopes, together with those for the odd-odd 276-d 254Es nuclide, were measured using a variety of α-particle and γ-ray spectroscopy techniques. Well-defined decay data are also essential pre-requisites for the detection and accurate characterization of fissile radionuclides. The parameters of greatest relevance include actinide half-lives, branching fractions, and α-particle and γ-ray energies and emission probabilities. Their quantification to good accuracy provides the means of monitoring their presence, behavior and transport in nuclear facilities as well as any clandestine movement and usage. As a consequence of recommendations made at recent IAEA research coordination meetings on “Updated Decay Data Library for Actinides,” measurements were undertaken to determine specific decay data of the more inadequately defined radionuclides. [ABSTRACT FROM AUTHOR]

N = Z nuclei have always had a special role in nuclear physics due to the symmetry of their wavefunctions, and their anomalously high binding energy. Beyond 56Ni they gain new significance, as they lie close to the proton dripline, and approaching 100Sn, they define the dripline. They are interesting for their structure, for rp-process nucleosynthesis, and as laboratories for weak interaction physics. In this paper I review some currently interesting topics and open questions. [ABSTRACT FROM AUTHOR]

The talk will focus on spin-dependent competition between oblate and prolate shape minima in the potential energy landscape of 180Hf (the most neutron-rich stable isotope), mediated via the alignment of valence nucleons. Results of a prompt spectroscopic study, using deep inelastic reactions with Gammasphere and CHICO, bombarding a thin 232Th target with a 180Hf beam ∼25% above the Coulomb barrier, will be presented. Nucleon alignments in both prolate and oblate minima will be discussed, as well as the favoring of oblate collective rotation at high spins, observed through a mixing with gamma vibrations built on the prolate shape. [ABSTRACT FROM AUTHOR]

A search for γ-ray transitions in 101Sn, which contains only one neutron outside the 100Sn core, was carried out at the Argonne Tandem-Linac Accelerator System. 101Sn nuclei were produced using the 46Ti(58Ni,3n)101Sn reaction. In-beam γ rays were detected in the Gammasphere Ge-detector array and were correlated with 101Sn β-delayed protons using the Recoil-Decay Tagging method. A γ-ray line at 172 keV was assigned to 101Sn and was interpreted as the transition between the single-neutron g7/2 and d5/2 states. The measured νg7/2-ν d5/2 energy splitting is compared with predictions of various mean-field potentials. It is also used to calculate multi-neutron configurations in light Sn isotopes. Prospects of using β-delayed protons for tagging other exotic nuclei in the 100Sn region are discussed. [ABSTRACT FROM AUTHOR]

α-decay is known in a few cases just above 100Sn. The lowest isospin nuclei in which it has been observed are the Tz=1 nuclei 114Ba, 110Xe, and 106Te. For the next lower isospin with Tz=1/2, N=Z+1, we used the reactions 58Ni + 58Ni and 58Ni + 54Fe to search for the 113Ba→109Xe→105Te→101Sn α-decay chain. We found no candidates in our study. We set upper limits on the production of 113Ba via the 58Ni + 58Ni reaction and upper limits on the production of 109Xe via the 58Ni + 54Fe reaction. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Gamma-rays from the nuclide 138Ce have been measured with the Gammasphere-array following Coulomb excitation. Beams of 138Ce ions were focussed on a carbon target at beam energies of 480 and 400 MeV. Gamma-ray yields and relative Coulomb excitation cross sections were measured in singles-mode. M1, E2, and E3 transition matrix elements from low-spin states were measured relative to the known B(E2; 01+ → 21+). The 2+ → 21+ M1 strength distribution from the lowest six 2+ states up to 2.7 MeV enables us to identify the 24+ state of 138Ce as the dominant fragment of the one-phonon 21,ms+ mixed-symmetry state with F-spin quantum number Fmax - 1. From its mixing with the nearby 23+ state an F-spin mixing matrix element of 44 keV can be estimated. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Coulomb excitation of Kπ=6+(t1/2=77 ns), 8-(t1/2=4.0 s) and 16+(t1/2=31 y) 178Hf isomers has led to the measurement of a set of Eλ matrix elements, coupling the isomer bands to the γ- and ground state bands. The resulting matrix elements, derived using a coupled-channel semiclassical Coulomb excitation search code, have been used to probe the K-components in the wave functions and revealed the onset and saturation of K-mixing in low-K bands, whereas K-mixing is negligible in the high-K bands. The implications can be applied to other quadrupole-deformed nuclei. An upper limit on the Coulomb depopulation yield of the 16+ isomer was calculated based on the present set of matrix elements. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The quasi-continuum of γ rays from the feeding and decay of superdeformed and normal bands in the nucleus 152Dy have been extracted in 1 - and 2 - dimensional spectra. The Eγ-Eγ correlations in the latter reveals strong ridges associated with superdeformed and normal states in this nucleus. The entry distributions for normal and superdeformed bands were also extracted. A Monte Carlo model was developed that simultaneously describes all the quasi-continuum and ridge spectra as well as the feeding intensity of the superdeformed bands. Through the calculation of the continuum of γ rays at finite temperature, the rotational damping widths in the normal and superdeformed wells were extracted. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The heavy-ion radiative capture reaction, 12C(12C,γ), has been investigated at beam energies around 16 MeV. Three different experiments were performed. Capture cross-sections were obtained by measuring fused 24Mg residues using the FMA at ANL. These were found to significantly exceed values reported earlier. Subsequently, the decay pathways associated with radiative capture were studied in two separate measurements: one with the high-resolution Gammasphere array and a second with a high efficiency BGO array, where gamma rays were recorded in coincidence with 24Mg residues detected at the focal plane of the DRAGON recoil separator at TRIUMF. Both measurements indicate that a substantial fraction of the decay is mediated through high-lying doorway states, possibly associated with the long-predicted shape-isomeric band in 24Mg. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The issue of correlations between protons and neutrons has become a major focus of nuclear structure research along the proton dripline. The strength of these correlations determined when nuclear binding ends. The correlations can have isospin T=1, just like &lrquo;normal” neutron-neutron and proton-proton pairs, or have more exotic structure in a deuteron-like T=0 configuration. I will discuss ways of studying these correlations and their relative importance. Odd-odd N=Z nuclei are good laboratories for this work. [ABSTRACT FROM AUTHOR]

In a series of experiments, [sup 48]Ca induced cold fusion reactions on Pb targets were employed to populate states in [sup 253,254]No isotopes. Evidence for decays from a rotational band built on a 7/2[624] configuration was obtained in [sup 253]No. The ground-state band of [sup 254]No is identified up to spin 20[sup +]. The deduced quadrupole deformation is β=0.27(2). The initial angular momentum and excitation energy of [sup 253,254]No residues, after neutron emission, was determined. States up to spin 22h and excitation energy of E[sup *]=8.5 MeV were observed. The data provide direct information on the fission barrier at high spins B[sub f]>=5 MeV, and on the shell-correction energy E[sub shell][sup exp]>=4.1 MeV. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The common feature to all superdeformed bands is the way they abrupty terminate when the nucleus suddenly changes shape. In most cases, it is extremely hard to tell how the nucleus then decays to its normally deformed groundstate, and this is why only very scarce information is available for superdeformed states. After a brief introduction on superdeformation, I will show, with a few examples, what is the status of our knowledge about the decay from superdeformed states. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]