A.-L. Hartig

Investigation of the nuclear matter distribution of 56Ni by elastic proton scattering in inverse kinematics

We have measured the nuclear-matter distribution of the doubly-magic N = Z nucleus Ni-56 by investigating elastic proton scattering in inverse kinematics. The radioactive beam of Ni-56 was injected and stored in the experimental storage ring (ESR, GSI) and interacted with an internal hydrogen gas-jet target. The high revolution frequency of the ions in the ring enabled a high luminosity, despite the low density of the target being used. This way, measurements at very low momentum transfers became possible. By measuring the energy and the scattering angle of the recoiling protons, we were able to separate the elastic reaction channel from inelastic scattering to the first excited 2(+) state of Ni-56 and deduced the differential cross section of Ni-56 (p, p)(56) Ni. The data were analyzed within the framework of the Glauber multiple-scattering theory in order to extract the nuclear-matter radius and radial matter distribution of Ni-56. Parameterizing the matter distribution with the phenomenological Symmetrized Fermi distribution, a preliminary value of 3.5 fm for the rms matter radius was deduced. This experiment was part of an EXL (EXotic nuclei studied in Light-ion induced reactions at storage rings) campaign at GSI in 2012 and was the first successful investigation of nuclear reactions with a stored radioactive beam ever.

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.

Isoscalar giant resonance studies in a stored-beam experiment within EXL

In the first campaign of the exotic nuclei studied with light-ion induced reaction in storage rings (EXL) collaboration at the existing storage ring experimental heavy-ion storage ring (ESR) at Helmholtz Center for Heavy Ion Research (GSI), we performed the first experiments using a stored beam of 58Ni and an internal helium gas-jet target aiming for the investigation of isoscalar giant resonances in inverse kinematics. In this experiment, inelastically scattered recoil particles (at very forward angles, °) were detected with a dedicated setup, including ultra-high vacuum (UHV)-compatible double-sided silicon strip detector (DSSDs). Preliminary results show evidence for the excitation of the isoscalar giant monopole resonance (ISGMR) in the 58Ni nucleus. This opens the opportunity to study in the near future giant resonances also with stored radioactive beams, like 56Ni, and extract important information about the nuclear matter incompressibility. In the present work the current status of the data analysis and results are shown and discussed.

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- Langevin via

^{132}

\gamma

Sn

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

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