Adam Maj IFJ PAN Krakow Search for Pigmy Dipole Resonance in 68 Ni RISING experiment in GSI EWON Meeting Prague, May, 2007

RISING Rare ISotope INvestigation at GSI The Accelerators: UNILAC (injector) E<11.5 MeV/n SIS 18Tm corr. U 1 GeV/n Beam Currents: pps FRS --> secondary radioactive ion beams: Fragmentation or fission of primary beams High secondary beam energies: 100 – 700 MeV/u Fully stripped ions Reactions on a secondary target Implantation inside a stopper Nuclear structure of exotic nuclei studied by Secondary fragmentation and Relativistic Coulomb excitation g-factor measurements Isomeric gamma and beta decay studies

EUROBALL Cluster Detectors Beam Tracking system + Miniball – Hector Why at ? Unique European facility for relativistic (  ≥ 0.4) exotic beams lifetime range ≥ 100 ns fully stripped beams Spin Aligned beams

EUROBALL Cluster Detectors Beam Tracking system + Miniball – Hector Fast Beam Campaign ( ) g-factor campaign (2005) – cf. D. Balabanski talk Stopped beam campaign (running )

Coulomb Excitation at Relativistic Energy EUROBALL Cluster Detectors Miniball: HPGe segmented detectors CATE : E-DE telescope event by event beam identification HECTOR Large 14.5 x 17 cm BaF 2 Detectors Relativistic Coulomb excitation of nuclei near 100 Sn New Shell structure at N>>Z Mirror symmetry of new (sub)shell closures : 36 S – 36 Ca Triaxiality in even-even core nuclei of N=75 isotones E1 Collectivity in neutron rich nuclei 68 Ni Fast Beam Campaign ( )

Cross-section for electromagnetic excitations

P N Average Transition charge densities Richter NPA 731(2004)59 Average Transition charge densities Richter NPA 731(2004)59 N GDR and PDR

 -decay of the Giant and Pigmy Dipole Resonaces Excited via relativistic Coulomb Excitation PDR have large impact on understanding of the r-process nucleosynthesis (S. Goriely. Phys. Lett. B436 (1998) 1)

Dipole strength shifts at low energy Collective or non-collective nature of the transitions? Stable nuclei  photoabsorption Exotic nuclei Virtual photon breakup LAND experiment Virtual photon scattering RISING experiment Question: How collective properties changes moving to neutron rich nuclei? T. Hartmann PRL85(2000) Ca 48 Ca Adrich et al. PRL 95(2005)132501

Coulomb excitation of 68 Ni (600 MeV A) 68 Ni Z AoQ Incoming 68 Ni beamOutgoing 68 Ni  E (Si) E (CsI) 1.2 % 4.4 % ~ 6 Days of effective beam time ~ 400 GB of data recorded ~ ‘ good 68 Ni events ‘ recorded

Coulomb excitation of 68 Ni (600 MeV A) Pygmy Dipole Resonance ? A structure appears at MeV in all detector types Preliminary Preliminary Preliminary A. Bracco et al., Acta Phys. Pol. B38, 1229 (2007), F. Camera et al., to be published Red lines – GEANT4 simulation assuming 10.8 MeV monoenergetic transition

Both RPA and RMF approaches predict for 68 Ni Pygmy strength at approximately 10.8 MeV for 68 Ni The degree of collectivity is still debated D. Vretnar et al. NPA 692(2001)496 RMF RPA G. Colo private communications 68 Ni ~ 10 MeV ~ 10 MeV CONCLUSIONS

COLLABORATION: Milano: A. Bracco, F. Camera, O. Wieland, G. Benzoni, S. Leoni, B. Million,… Kraków: P. Bednarczyk, J. Grębosz, M. Kmiecik, A. Maj, K. Mazurek, W. Męczyński, J. Styczeń GSI: T. Aumann, H.J. Wollersheim, J. Gerl, I. Kojouharow,…. Legnaro: G. de Angelis, A. Gadea, D. Napoli,.. Sofia/Camerino: D. Balabanski