To investigate the low-spin structure of 84Sr and 86Sr, two fusion-evaporation experiments using the (p,2n) reaction have been performed. The data have been evaluated in terms of γ-ray spectroscopy, i.e. the level scheme was built up, branching intensities were determined, nuclear state spin and parity assignments were made after γγ angular correlation analyses. The previously known level scheme information was extended. In addition, lifetimes were determined by means of the Doppler Shift Attenuation Method (DSAM). In 86Sr, a new method for lifetime determinations, the Spectral Difference Method (SDM), was applied for the first time. In cases where all necessary input variables were known, reduced transition strengths were calculated with Monte Carlo simulated probability density functions. It is stressed that linear error propagation for the calculated errors of reduced transition strengths is not universally applicable. As both nuclei lie in the vicinity of the N=50 neutron shell closure and on a possible proton subshell closure of the 2p3/2 orbital at Z=38, Nuclear Shell Model calculations for 84Sr, 86Sr, and 88Sr have been performed in the truncated (2p3/2, 1f5/2, 2p1/2, 1g9/2) model space for protons and neutrons with the empirical JUN45 residual interaction. The comparison between experimental results and theoretical predictions show a large degree of consistency.

Excited low-spin states in 96Mo and 98Mo have been studied in γγ angular correlation experiments in order to determine spins and multipole mixing ratios. Furthermore, from a Doppler lineshape analysis effective lifetimes τ in the femtosecond range were obtained. The experimental data show a complex spectrum due to configuration mixing, which is confirmed by Interacting Boson Model calculations based on a Skyrme energy density functional. The M1-transition strengths of transitions depopulating excited 2+ states to the first 2+ state are discussed in terms of the proton–neutron mixed symmetry.

We propose to use fast-timing and γ spectroscopy to study five nuclei including the doubly magic Sn and its four neighbours: two-neutron hole Sn, one-neutron hole Sn, one-neutron particle Sn and two-neutron particle Sn. There is an increasing interest in these nuclei since they serve to test nuclear models using state-of-the-art interactions and many body approaches, and they provide information relevant to deduce single particle states. In addition properties of these nuclei are very important to model the astrophysical r-process. The present ISOLDE facility provides unique capabilities to study these Sn nuclei populated in the β-decay of In isomers, produced from a UCx target unit equipped with neutron converter and ionized with RILIS, capable of selective isomer ionization. The increased production yields for In are estimated to be 200 larger than in the previous work done at OSIRIS. We will use the recently commissioned Isolde Decay Station (IDS), slightly modified to improve the efficiency of fast-timing measurements. Compared to earlier measurements in this region the sensitivity will be enhanced by the use of the highly-efficient clover-type Ge detectors and the new generation fast-timing LaBr3(Ce) crystals. Requested shifts: 27 shifts (split into 1 run over 1 year) 1 Experimental and theoretical framework Doubly-magic nuclei and their immediate neighbours command a strong interest for both theoretical and experimental investigations [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]. They represent the best regions to test the shell-model effective Hamiltonian, namely the single particle energies and two-body matrix elements of the residual interaction, as well as the effective electromagnetic operators, which are then used in model calculations over an extended range of the nuclide chart. For the vast region of the medium heavy nuclei, there are only two doubly-magic nuclei, stable Pb and exotic Sn, which can be studied in greater detail. Sn isotopes are very special since those that can be studied experimentally span a long range, starting from the doubly magic Sn to Sn, and now extending even to Sn [1]. The interest in the Sn nucleus and the difficulty in accessing it, can be illustrated by the fact that in the last 20 years there were about 500 theoretical studies on this nucleus but only a few experimental investigations of its excited states. Realistic shell-model calculations have proved to lead to a good description of nuclear structure around Sn [9]. In these calculations, the two-body matrix elements of the shell-model effective Hamiltonian are constructed by means of many-body perturbation theory starting from a low-lomentum interaction derived from the high-precision CD-Bonn nucleon-nucleon potential. The chosen model space includes the 6 neutronparticle orbitals 0h9/2 1f7/2, 1f5/2, 2p3/2, 2p1/2, 0i13/2, and the 5 neutron-hole orbitals 0g7/2, 1d5/2, 1d3/2, 2s1/2, 011/2 for tin isotopes with N >82 and N<82, respectively. The values of the single-particle and single-hole energies are taken from experiment, and more precisely, whenever available, from the spectra of Sn and Sn. Proton and neutron excitations across the 50 and 82 shells are not explicitly included in the calculations but are accounted for by the core polatization contributions to the effective interaction. It is worth mentioning also that this nuclear region is important to the understanding

The recoil distance Doppler-shift method (RDDS) is a very valuable technique for measuring lifetimes of excited nuclear states in the picosecond range to deduce absolute transition strengths between nuclear excitations independent on the reaction mechanism. Therefore, we propose an experiment on the N=52 nucleus Se with Coulomb excitation in inverse kinematics to implement this method at HIE-ISOLDE using a new plunger device that will be developed and built by our Cologne group for a first RDDS measurements in combination with MINIBALL. In the region of neutron-rich nuclei nearby N=50 the question arises whether the magic nucleon numbers survive at large values of the isospin. Existing experimental results in this region indicate a weakening of the N=50 shell gap towards Ge (Z=32) and an increase in the region of Zn. Our experiment aims to prove this observation by a measurement of absolute E2 transition strengths in Se which, in addition, enables to test model predictions in the shell model, the interacting boson model and collective models. Such were already applied to heavier nuclei in this region allowing a detailed interpretation of the structure regarding the evolution of collective phenomena in and proton subshell closures for Sr and Zr isotopes near N=50 and their disappearance for these isotopes more far from N=50.

A Mo100(α,2n)Ru102 fusion evaporation experiment, performed at the HORUS cube spectrometer at the Cologne FN-Tandem accelerator, is presented and discussed. Via the analysis of γγ coincidences, it was possible to extend the level scheme with 40 new levels and 81 decays. Several new spins and multipole mixing ratios were determined using the γγ angular correlation technique. In addition, a DSAM analysis was performed and 14 new effective lifetimes were determined in the femtosecond range. Thus, several effective transition strengths were determined. Investigating the phononic structure, candidates for the quadrupole–octupole phonon multiplet 21+⊗31− were found. The data is compared to calculations within the Interacting Boson Model (IBM-1) in the U(5) limit, the O(6) limit as well as a transitional class U(5)–O(6). The low spin level energies show characteristics of multiphonon excitations and point towards 102Ru resembling an anharmonic vibrational nucleus. The B(E2) transition strengths do not exactly match this picture, and are described in a better way using the U(5)–O(6) calculation.

This proposal aims at the study of the neutron-rich region around the doubly-magic nucleus Pb populated via a multinucleon transfer reaction. An unstable Rb beam will be delivered by HIE-ISOLDE at 5.5 MeV·u onto a Pb 13.0 mg/cm target. The γ rays will be recorded by the MINIBALL γ-ray spectrometer. The aim of the experiment is twofold: i) firstly it will represent the proof of principle that multinucleon transfer reactions with neutron-rich unstable beams is efficient to populate neutron-rich heavy binary partners and represents a competitive method to cold fragmentation ii) secondly we aim at populating mediumto high-spin states in Pb and Hg to elucidate the existence of the 16 isomer in the lead isotopes and at the same time to disentangle the puzzling case of a very low energy 3− state in Hg not described by any nuclear model. The experimental results will be compared with large-scale shell-model calculations using the realistic Kuo-Herling interaction that involves a large valence space. This comparison will help to elucidate the role of effective three-body forces in this region and the possible structure change in Hg. Requested shifts: 27 shifts, (split into 1 run over 1 year) Installation: [MINIBALL] 1 Scientific motivation The shell model is nowadays able to provide a comprehensive view of the atomic nucleus. It is a many-body theoretical framework, successful in explaining various features of the structure of nuclei, based on the definition of a restricted valence space where a suitable Hamiltonian can be diagonalized. For example the shell model has been capable to explain the magic numbers, as a key feature in finite fermionic systems, as well as its evolution when going away from the stability line. In the last years, theoretical predictions and experimental results have indicated that magic numbers can change depending on the N/Z ratio, thus implying a more local applicability [1, 2, 3]. For instance, the tensor component of the residual interaction is expected to strongly depend on the specific orbits being filled and acts in all nuclear regions, not necessarily close to the drip-lines [4, 5]. The regions around double-shell closures are a benchmark for the study of nuclear structure since they are a direct source of information on the nucleon-nucleon effective interaction in nuclei. These regions have been mostly studied for light and medium-mass nuclei, using fission, deep-inelastic and transfer reactions. However, the region around the heaviest doubly-magic nucleus known in the whole Segré chart, i.e. the Pb, is particularly difficult to reach experimentally and has not been thoroughly explored so far, due to its high mass and neutron richness. As a consequence, spectroscopic information on neutron-rich lead and nearby isotopes are rather scarce. Pioneering work in this area by using multinucleon transfer reaction with stable beams has been done by Broda and collaborators [6, 7], where using stateof-the-art Compton suppressed large γ-ray arrays they managed to measure high-spin yrast states in many different isotopes. However, the most neutron-rich isotope that they

A gamma gamma angular-correlation experiment has been performed to investigate the low-energy states of the nucleus Mo-98. The new data, including spin assignments, multipole mixing ratios, and lifetimes reveal evidence for shape coexistence and mixing in Mo-98, arising from a proton intruder configuration. This result is reproduced by a theoretical calculation within the proton-neutron interacting boson model with configuration mixing, based on microscopic energy density functional theory. The microscopic calculation indicates the importance of the proton particle-hole excitation across the Z = 40 subshell closure and the subsequent mixing between spherical vibrational and the gamma-soft equilibrium shapes in Mo-98.

C. Sotty1, P. Van Duppen1, M. Huyse1, L.M. Fraile2, A. Algora3, A. Andreyev4, M.L.L. Benito5, S. Bönig6, C. Borcea7, R. Borcea7, B. Cheal8, T.E. Cocolios9, H. De Witte1, H. Duckwitz10, P. Fernier5, F. Flavigny1, L. Gaffney1, T. Grahn11,12, P.T. Greenless11,12, S. Ilieva6, J. Jolie10, R. Julin11,12, U. Koester13, T. Kröll6, R. Lica7, H. Mach15, N. Mărginean7, R. Mărginean7, C. Mihai7, F. Negoita7, A. Negret7, B. Olaizola2, R. Page8, J. Pakarinen11,12, S. Pascu7, V. Paziy2, E. Piselli5, D. Radulov1, E. Rapisarda5, F. Rotaru7, M. Stanoiu7, O. Tenglad14, T. Thomas10, M. Thürauf6, J.M. Udías2, V. Vedia2, D. Voulot5, W.B. Walters16, N. Warr10, F. Wenander5.

This proposal aims at the study of the single particle properties of the neutron-rich nickel isotopes, specifically of the Ni isotope via a Ni(d,p)Ni reaction. The Ni beam will be delivered by HIE-ISOLDE at 5.5 MeV/u onto a 1.0 mg/cm CD2 target. The protons produced in the (d,p) reaction will be detected with the T-REX silicon array either in singles or in coincidence with γ rays recorded by MINIBALL. The experimental results will be compared with large-scale shell-model calculations using effective interactions that involve large valence spaces for protons and neutrons, with excitations beyond the Z=28 and N=50 shell gap. This comparison will permit the study of the single-particle orbital d5/2 that together with the quasi-SU3 partner g9/2 gives rise to the collectivity in this region and has direct implications on the Ni. Requested shifts: 39 shifts, (split into 1 run over 1 year) Installation: [MINIBALL + T-REX] 1 Scientific motivation Magic numbers are a key feature in finite fermionic systems since they are strongly related to the underlying mean field. Their existence and stability suggested the presence of closed shell configurations which led to the development of the Shell Model of atomic nuclei. Recently, theoretical predictions and experimental results have indicated that magic numbers can change depending on the N/Z ratio, thus implying a more local applicability [1, 2, 3]. For example, the tensor component of the residual interaction is expected to strongly depend on the specific orbits being filled and acts in all nuclear regions, not necessarily close to the drip-lines [4, 5]. The tensor force results in the attraction between orbitals with anti-parallel spin configuration and a repulsion between orbitals with parallel spin configuration. Recently, structural changes in different mass regions due to the tensor mechanism have been discussed [6, 7, 8, 9, 10]. The magic numbers at N=20 and 28 disappear with increasing N/Z ratio and new magic numbers at N=14, 16 and 32 seem to appear. It is also predicted that the Z=28 gap for protons in the pf-shell reduces when moving from Ni to Ni, as a result of the attraction between the proton f5/2 and the neutron g9/2 orbits and the repulsion between the proton f7/2 and neutron g9/2 configurations, thus modifying or even inverting the effective single particle states. It is by now well established that the Ni isotope presents a subshell gap at N=40, confirmed by various recent studies and initially suggested by the discovery of its second excited 0 state and a large excitation energy for the 2 state (2033 keV) [11, 12]. Since the properties of Ni are still questioned, neutron-rich Ni, Co and Cu isotopes have been the object of many theoretical and experimental studies. Specifically, the neutron-rich Ni region has been experimentally studied via intermediate-energy Coulomb excitation [13], beta decay [14], transfer reactions [15, 16] and recently via lifetimes measurements of the 2 states of very neutron-rich Ni isotopes at MSU. This list does not pretend to be exhaustive since new publications appear almost daily in refereed journals. A step forward in the understanding of the region and the nature of the NN interac-

It is proposed to investigate the microscopic mechanism which leads to a concentration or a fragmentation of the quadrupole-collective isovector valence-shell excitations, the so-called mixed-symmetry states (MSSs), an effect called shell stabilization of MSSs. This aim will be achieved by identification of MSSs of the unstable nuclei Nd and Sm. The first steps of this program have been undertaken in two subsequent REX-ISOLDE experiments (IS496) in which we have measured the B(E2; 21 → 01 ) transition strengths in the radioactive nuclei Nd and Sm. By using these data and the higher beam energy of HIE-ISOLDE we propose now to identify the MSSs of these nuclei by measuring their relative populations with respect to the population of the first 2 states in Coulomb excitation (CE) reactions. Requested shifts: 42 shifts (can be split into 2 runs (18+24 shifts) over 2 years) Installation: [MINIBALL + CD-only] or [MINIBALL + T-REX]

We put forward a study of the interplay between individual nucleon behavior and collective degrees of freedom in the nucleus, as manifested in shape coexistence in the neutrondeficient lead region. As a first step of this experimental campaign, we propose to perform Coulomb excitation on light mercury isotopes to probe their excited states and determine transitional and diagonal E2 matrix elements, especially reducing the current uncertainties. The results from previous Coulomb excitation measurements in this mass region performed with 2.85 MeV/u beams from REX-ISOLDE have shown the feasibility of these experiments. Based on our past experience and the results obtained, we propose a detailed study of the 182-184Hg nuclei, that exhibit a pronounced mixing between low-lying excited states of