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Search for Pygmy Dipole Resonance in 68Ni: Insights from the RISING Experiment at GSI

This presentation discusses the ongoing research into the Pygmy Dipole Resonance (PDR) in the isotope 68Ni, conducted at the RISING facility at GSI. Utilizing relativistic Coulomb excitation, we aim to explore the nuclear structure of this exotic nucleus, revealing insights into its dipole strength and the associated collective properties. The experiment recorded significant data on electromagnetic excitations, contributing to our understanding of r-process nucleosynthesis. The results from various computational models predicting the collective nature of these transitions will also be addressed.

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Search for Pygmy Dipole Resonance in 68Ni: Insights from the RISING Experiment at GSI

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  1. Adam Maj IFJ PAN Krakow Search for Pigmy Dipole Resonance in 68Ni RISING experiment in GSI EWON Meeting Prague, 10-12 May, 2007

  2. RISINGRare ISotope INvestigation at GSI • The Accelerators: • UNILAC(injector) E<11.5 MeV/n • SIS 18Tmcorr. U 1 GeV/n • Beam Currents: 108 - 109 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 bySecondary fragmentation and Relativistic Coulomb excitation • g-factor measurements • Isomeric gamma and beta decay studies

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

  4. Fast Beam Campaign (2003-2005) g-factor campaign (2005) – cf. D. Balabanski talk Stopped beam campaign (running) EUROBALL Cluster Detectors Beam Tracking system + Miniball – Hector

  5. Fast Beam Campaign (2003-2005) EUROBALL Cluster DetectorsMiniball: HPGe segmented detectors HECTOR Large 14.5 x 17 cm BaF2 Detectors CATE : E-DE telescope event by event beam identification Coulomb Excitation at Relativistic Energy • Relativistic Coulomb excitation of nuclei near 100Sn • New Shell structure at N>>Z • Mirror symmetry of new (sub)shell closures : 36S – 36Ca • Triaxiality in even-even core nuclei of N=75 isotones • E1 Collectivity in neutron rich nuclei 68Ni

  6. Cross-section for electromagnetic excitations

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

  8. g-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)

  9. 48Ca 40Ca Adrich et al. PRL 95(2005)132501 T. Hartmann PRL85(2000)274 Question: How collective properties changes moving to neutron rich nuclei? 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

  10. Incoming 68Ni beam 68Ni AoQ Z Coulomb excitation of 68Ni (600 MeV A) Outgoing 68Ni E (CsI) 1.2 % 4.4 % DE (Si) ~ 6 Days of effective beam time ~ 400 GB of data recorded ~ 3 107 ‘ good 68Ni events ‘ recorded

  11. Coulomb excitation of 68Ni (600 MeV A) Pygmy Dipole Resonance ? Preliminary Preliminary Preliminary Red lines – GEANT4 simulation assuming 10.8 MeV monoenergetic transition A structure appears at 10-11 MeV in all detector types A. Bracco et al., Acta Phys. Pol.B38, 1229 (2007), F. Camera et al., to be published

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

  13. 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

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