S. Bönig

First Nuclear Reaction Experiment with Stored Radioactive 56Ni Beam and Internal Hydrogen and Helium Targets

The investigation of light-ion induced direct reactions using stored and cooled radioactive beams, interacting with internal targets of storage rings, can lead to substantial advantages over external target experiments, in particular for direct reaction experiments in inverse kinematics at very low momentum transfer, q. This new and challenging experimental technique enables high-resolution measurements down to very low q and provides a gain in luminosity from accumulation and recirculation of the stored beams. For performing first experiments of this kind a dedicated experimental setup housing several DSSD (Double-sided Silicon Strip Detector) and Si(Li) detectors for recoil particles, well suited for meeting the demanding UHV (Ultra High Vacuum) conditions of a storage ring, was recently designed, constructed and installed at the internal target of the ESR storage ring at GSI. From the interaction of a stored 56Ni beam with an internal H2 target, good quality differential cross section data for elastic proton scattering, measured with the aim to determine the radial shape of the nuclear matter distribution of 56Ni, were obtained. Preliminary results are presented. Being the first reaction experiment ever performed with a stored radioactive beam on a world-wide scale, this experiment can be considered as a breakthrough for nuclear structure and astrophysics studies, and, in addition, as a successful proof-of-principle of the new experimental concept. In addition, preliminary results from a feasibility study on inelastic α-scattering from 58Ni in inverse kinematics, where it was demonstrated that the Isoscalar Giant Monopole Resonance in 58Ni can be investigated by the present technique down to CM angles below 1 degree, are discussed. Such an experiment, performed in the future with the doubly magic 56Ni, would provide important information on the EOS of nuclear matter.

Nuclear reactions in the storage ring ESR with EXL

The EXL project aims to study nuclear structure by direct reactions in inverse kinematics at the storage rings of the future FAIR facility. In this contribution, we present the status of the project: the technical implementation at the ESR at GSI and preliminary results of the EXL campaign in 2012, the first using also a radioactive beam.

Lifetime Measurements in Neutron-rich Xe Isotopes - Evolution of Quadrupole Collectivity Beyond

Picosecond lifetimes of excited states in neutron-rich Xe isotopes were measured at the Institut Laue- nLangevin via

^{132}

gamma

Sn

-ray spectroscopy of fission fragments from neutron-induced fission of 235U and 241Pu ntargets. The data collected with the recently installed fast timing array FATIMA in combination with nthe EXOGAM Ge array were analysed using the new generalized centroid difference method. Our naim is to study the quadrupole and octupole collectivity, arising in the mass region beyond the doubly nmagic 132Sn, by means of transition probabilities. These can be calculated from the directly measured nlifetimes.

Status of the analysis of the first EXL experiment at the ESR

M. von Schmid †1, J.C. Zamora1, S. Bagchi 2, S. B̈onig1, M. Csatĺos3, I. Dillmann4, C. Dimopoulou4, P. Egelhof 4, V. Eremin5, T. Furuno6, H. Geissel 4, R. Gernḧauser7, M.N. Harakeh2, A-L. Hartig1, S. Ilieva1, N. Kalantar-Nayestanaki 2, O. Kiselev4, H. Kollmus4, C. Kozhuharov 4, A. Krasznahorkay 3, T. Kröll1, M. Kuilman2, S. Litvinov4, Yu.A. Litvinov4, M. Mahjour-Shafiei 2,8, M. Mutterer4, D. Nagae9, M.A. Najafi2, C. Nociforo4, F. Nolden4, U. Popp4, C. Rigollet2, S. Roy2, C. Scheidenberger 4, M. Steck4, B. Streicher 2,4, L. Stuhl 3, M. Tḧurauf1, T. Uesaka10, H. Weick4, J.S. Winfield4, D. Winters4, P.J. Woods 11, T. Yamaguchi 12, K. Yue1,4,13, J. Zenihiro10 for the EXL collaboration‡1 1IKP, TU Darmstadt;2Univ. of Groningen, KVI-CART, Groningen; 3MTA-Atomki, Debrecen;4GSI, Darmstadt; 5PTI, St. Petersburg; 6Kyoto University; 7TU München; 8University of Tehran;9University of Tsukuba; 10RIKEN, Tokio; 11University of Edinburgh;12Saitama University;13IMP, Lanzhou

Quadrupole collectivity in neutron-rich Cd isotopes

The proximity to the closed shells at Z = 50 and N = 82 makes the neutron-rich Cd isotopes a perfect test case for nuclear theories. The energy of the first excited 2+-state in the even 122-128 shows an irregular behaviour as the Cd isotopes exhibit only a slight increase for 122Cd to 126Cd and even a decrease from 126Cd to 128Cd. This anomaly can so far not be reproduced by shell model calculations. Only beyond mean field calculations with a resultant prolate deformation are capable to describe this anomalous behaviour. In order to gain more information about the neutron-rich Cd isotopes a Coulomb excitation experiment was performed with MINIBALL at REX-ISOLDE, CERN. The extracted transition strengths B (E2,0+gs → 2+1) for 122,124,126,128Cd agree with beyond mean field calculations. The spectroscopic quadrupole moments Qs (2+1) are compared with measurements on odd neutron-rich Cd isotopes.