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High-seniority excitations above the 10+ and 27/2- isomeric states were investigated with gamma coincidence techniques in neutron-rich Sn isotopes produced in fission processes following 48Ca+208Pb, 48Ca+238U and 64Ni+238U reactions. In the data analysis, the delayed gamma coincidence technique was used to establish high-spin state structures in all Sn isotopes with isomeric half-lives below 10 µsec. For cases with long-lived isomeric states, the gamma cross-coincidence method was employed to identify such structures. The relevant features of the fusion-fission process were investigated to enable these identifications. The discussion of some details of these analyses is followed by two examples of the results obtained: the 124Sn level scheme and the level energy systematics for selected states established in even Sn isotopes. [ABSTRACT FROM AUTHOR]

The nucleus $\ensuremath {\rm ^{127}Sb}$ , which is on the neutron-rich periphery of the $\ensuremath \beta$ -stability region, has been populated in complex nuclear reactions involving deep-inelastic and fusion-fission processes with $\ensuremath {\rm {}^{136}Xe}$ beams incident on thick targets. The previously known isomer at 2325 keV in $\ensuremath {\rm {}^{127}Sb}$ has been assigned spin and parity $\ensuremath 23/2^+$ , based on the measured $\ensuremath \gamma$ - $\ensuremath \gamma$ angular correlations and total internal conversion coefficients. The half-life has been determined to be 234(12) ns, somewhat longer than the value reported previously. The 2194 keV state has been assigned $\ensuremath J^{\pi} = 19/2^+$ and identified as an isomer with $\ensuremath T_{1/2} = 14(1) {\rm ns}$ , decaying by two $\ensuremath E2$ branches. The observed level energies and transition strengths are compared with the predictions of a shell model calculation. Two $\ensuremath 15/2^+$ states have been identified close in energy, and their properties are discussed in terms of mixing between vibrational and three-quasiparticle configurations. [ABSTRACT FROM AUTHOR]

Resonances in light heavy ion reactions are a much studied but little understood phenomenon. New measurements are reported of the 12C(12C,γ)24Mg radiative capture reaction with the aim of performing spectroscopic measurements on the previously identified resonances. The preliminary analysis is outlined relating to the identification of the 24Mg using a triple ion chamber setup. [ABSTRACT FROM AUTHOR]

The energies of 2-quasiparticle (2-qp) states in heavy shell-stabilized nuclei provide information on the single-particle states that are responsible for the stability of superheavy nuclei. We have calculated the energies of 2-qp states in 256Rf, which suggest that a long-lived, low-energy 8- isomer should exist. A search was conducted for this isomer through a calorimetric conversion electron signal, sandwiched in time between implantation of a 256Rf nucleus and its fission decay, all within the same pixel of a double-sided Si strip detector. A 17(5)-μs isomer was identified. However, its low population, ∼5(2)% that of the ground state instead of the expected ∼30%, suggests that it is more likely a 4-qp isomer. Possible reasons for the absence of an electromagnetic signature of a 2-qp isomer decay are discussed. These include the favored possibility that the isomer decays by fission, with a half-life indistinguishably close to that of the ground state. Another possibility, that there is no 2-qp isomer at all, would imply an abrupt termination of axially symmetric deformed shapes at Z = 104, which describes nuclei with Z = 92-103 very well. [ABSTRACT FROM AUTHOR]

A detailed level scheme for 221Th has been established in an experiment using the 18O + 207Pb reaction at 96 MeV. The evaporation residues from this fissile system were selected with the HERCULES detector array and residue-gated γ rays were measured with Gammasphere. Three band structures of interlinked, alternating-parity levels are observed, two of which are non-yrast. In addition, several high-lying excitations are found. The yrast band is seen up to spin-parity 37/2- and 39/2+, beyond which a high-spin feeding transition is observed. The non-yrast sequences are interpreted as parity-doublet structures, based on a configuration similar to that of the yrast band in 223Th (K = 5/2). The key properties of even-odd nuclei in this mass region [B(E1)/B(E2) and B(M1)/B(E2) ratios, spin alignments, parity splittings] are reviewed. [ABSTRACT FROM AUTHOR]

Abstract: New spectroscopic results for high-spin states in 192Os populated in deep-inelastic reactions include the identification of a 2-ns, 12+ isomeric state at 2865 keV and a 295-ns, 20+ state at 4580 keV and their associated sequences. The structures are interpreted as manifestations of maximal rotation alignment within the neutron and proton shells at oblate deformation. Rotational band members based on the long-lived, isomer are also identified for the first time. Configuration-constrained, potential-energy-surface calculations predict that other prolate multi-quasiparticle high-K states should exist at low energy. [Copyright &y& Elsevier]

Excited states in 64Ni, 66Ni, and 68Ni were populated in quasielastic and deep-inelastic reactions of a 430-MeV 64Ni beam on a thick 238U target. Level schemes including many nonyrast states were established up to respective excitation energies of 6.8, 8.2, and 7.8 MeV on the basis of γ-ray coincidence events measured with the Gammasphere array. Spin-parity assignments were deduced from an angular-correlation analysis and from observed γ-decay patterns, but information from earlier γ-spectroscopy and nuclear-reaction studies was used as well. The spin assignments for nonyrast states were supported further by their observed population pattern in quasielastic reactions selected through a cross-coincidence technique. Previously established isomeric-state decays in 66Ni and 68Ni were verified and delineated more extensively through a delayed-coincidence analysis. A number of new states located above these long-lived states were identified. Shell-model calculations were carried out in the p3/2f5/2p1/2g9/2 model space with two effective interactions using a 56Ni core. Satisfactory agreement between experimental and computed level energies was achieved, even though the calculations indicate that all the states are associated with rather complex configurations. This complexity is illustrated through the discussion of the structure of the negative-parity states and of the Ml decays between them. The best agreement between data and calculations was achieved for 68Ni, the nucleus where the calculated states have the simplest structure. In this nucleus, the existence of two low-spin states reported recently was confirmed as well. Results of the present study do not indicate any involvement of collective degrees of freedom and confirm the validity of a shell-model description in terms of neutron excitations combined with a closed Z = 28 proton shell. Further improvements to the calculations are desirable. [ABSTRACT FROM AUTHOR]

New high-spin microsecond isomers, with Jπ = (31+) and Jπ = (28-), have been identified in 206Bi at 10 170 and 9233 keV, respectively, using γ-ray coincidence spectroscopy following deep-inelastic reactions with the 76Ge + 208Pb system. Yrast and near-yrast levels populated in the decay of these isomers have been located and interpreted with the help of shell-model calculations. The states identified at energies up to approximately 7 MeV can be described well in terms of one-proton-particle, three-neutron-hole couplings. [ABSTRACT FROM AUTHOR]

High-spin states in the odd-proton thulium isotopes 173Tm and 175Tm have been studied using deep-inelastic reactions and γ-ray spectroscopy. In l73Tm, the low-lying structure has been confirmed and numerous new states have been identified, including a three-quasiparticle Kπ = 19/2- isomer with a lifetime of τ = 360(100) ns at 1906 keV and a five-quasiparticle Kπ = 35/2- isomer with a lifetime of τ = 175(40) ns at 4048 keV. The Kπ = 35/2- state is interpreted as a t-band configuration that shows anomalously fast decays. In 175Tm, the low-lying structure has been reevaluated, a candidate state for the 9/2- [514] orbital has been identified at 1175 keV, and the 7/2-[523] bandhead has been measured to have a lifetime of τ = 460(50) ns. Newly identified high- AT structures in 175Tm include a Kπ = 15/2- isomer with a lifetime of τ = 64(3) ns at 947 keV and a Kπ = 23/2- isomer with a lifetime of τ = 30(20) µs at 1518 keV. The Kπ = 15/2- isomer shows relatively enhanced decays to the 7/2-[523] band that can be explained by chance mixing with the 15/2- member of the 7/2- band. Multiquasiparticle calculations have been performed for 173Tm and l75Tm, the results of which compare well with the experimentally observed high-spin states. [ABSTRACT FROM AUTHOR]

A y-ray spectroscopy study of 30S is presented. Excitation energies have been determined with improved precision over previous studies and firm spin-parity assignments have been made for key 29P + p resonant states. An evaluation of the 29P(p, y)30S reaction for T = 0.08-2.5 GK shows that the 3+ and 2+ resonant states located at Er = 289(3) and 410(3) keV, respectively, dominate the 29P(p, y)30S reaction rate in ONe novae, while the 410-keV resonance is expected to govern the rate in x-ray burster environments. These new, precise resonance energy measurements and firm spin-parity assignments have significantly reduced uncertainties in the 29P(p, y )30S reaction in ONe novae and x-ray bursts. In particular, the reaction rate is now specified precisely enough for calculations of isotopic abundances in ONe novae ejecta. [ABSTRACT FROM AUTHOR]

An experimental study of the 62Zn nucleus has been performed by combining the data sets from four fusion-evaporation reaction experiments. Apart from the previously published data, the present results include ten new rotational band structures and two more superdeformed bands. The Gammasphere Ge-detector array in conjunction with the 4? charged-particle detector array Microball allowed for the detection of γ rays in coincidence with evaporated light particles. The deduced level scheme includes some 260 excited states, which are connected with more than 450 λ-ray transitions. Spins and parities of the excited states have been determined via directional correlations of λ rays emitted from oriented states. The experimental characteristics of the rotational bands are analyzed and compared with results from cranked Nilsson-Strutinsky calculations. The present analysis, combined with available experimental results in the A ~ 60 mass region, can be used to improve the current set of Nilsson parameters in the N = 3 and N = 4 oscillator shells. [ABSTRACT FROM AUTHOR]

The nuclei 65-67Cu were studied in reactions between a 430-MeV 64Ni beam and a thick 238U target with the Gammasphere array. Decay schemes for both nuclei have been extended, with spin and parity assignments of observed states constrained by measured &ggr;-ray angular distributions and correlations. Positive-parity level structures, based on p3/2 protons coupled to negative-parity states in the Ni cores, have been identified above the known 9/2+ states. In 67Cu, a negative-parity dipole band built upon a πf-17/2 state has been observed, as were two shorter negative-parity sequences. A qualitative description of the level structures has been obtained through comparison with systematics of the odd-A57-51Cu isotopes and with states in the neighboring even-even Ni and Zn cores. Shell-model calculations using JUN45 and jj44b effective interactions were performed for 65,67Cu, with jj44b providing overall better agreement with the data. Both are limited, however, by the restriction that the f7/2 and g9/2 orbitals are not available simultaneously in the basis. Proton f7/2 and neutron g9/2 orbitals are required for the full negative-parity spectrum of states, while g9/2 protons and neutrons are both important for positive-parity levels. The latter states are found to be better described in terms of weak coupling of a proton to the Ni core. [ABSTRACT FROM AUTHOR]

Gamma rays assigned to Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. have been identified with Gammasphere in deep-inelastic reactions involving a 450-MeV 76Ge beam and a 198Pt target. Using a combination of spectra produced by double gates on the known 454-, 843-, and 1095-keV members of the ground-state cascade, a coincident line at 199 keV has been identified and is tentatively assigned as the 8+ → 6+ transition. These γ-ray coincidences have been observed only in prompt events, indicating an 8+ half-life below 20 ns and requiring a large B(E2) enhancement compared to that expected from a seniority scheme. This value is consistent with models showing decay to a seniority v = 4, 6+ level that is depressed by the same two-body interaction responsible for the rather low 1095-keV Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. energy, as compared to the valence-symmetry counterpart Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. [ABSTRACT FROM AUTHOR]

The magnetic moments of Iπ=21+ states in even–even A∼100 fission fragments have been measured using the Gammasphere array, using the technique of time-integral perturbed angular correlations. The data are interpreted within the context of the interacting boson model (IBA2) leading to the suggestion of a strong νh11/2 component in the deformed 21+ states of this region. [Copyright &y& Elsevier]

Excited states of the neutron deficient 101Ag nucleus have been investigated via the 50Cr(58Ni, 3p1α) heavy-ion induced reaction at 261 MeV by use of in-beam spectroscopic methods. On the basis of the measured γγ-coincidence relations and angular distribution ratios high-spin bands have been extended up to Iπ=35/2+, 45/2(−) and (49/2−). The negative parity states at the highest energy have been interpreted as terminating non-collective oblate states in the framework of the Nilsson–Strutinsky cranking formalism. [Copyright &y& Elsevier]

A new approach to the production of low energy radioactive beams involves the stopping of fast beams produced by fragmentation, in-flight fission or fusion–evaporation reaction into a large gas catcher where the reaction products are thermalized in high-purity helium and extracted as singly charged ions for post-acceleration. This removes the limitation present in standard ISOL technique for species that are difficult to extract from the target/ion source assembly. This approach has been implemented at Argonne since 1998 to inject fusion–evaporation products in an ion trap system. Via a series of improvements since then, we now reach efficiencies for these devices of close to 50% with delay times below 10 ms. In preparation for the RIA project, a larger device for stopping fragmentation products is in preparation. The basic principles behind these devices together with results obtained and experience gained operating these devices will be presented. Preparation for a test of the large gas cell at the full RIA energy at GSI will also be presented. [Copyright &y& Elsevier]