Nuclear Structure studies using fast radioactive beams J. Gerl SNP2008 July Ohio University, Athens Ohio USA –The RISING experiment –Relativistic Coulomb excitation –Spin degree of freedom in fragmentation reactions –Open questions and future experimental possibilities

252 Coulomb excitation, Fragmentation and Decay studies using Rare Isotope Beams and high-resolution  Spectroscopy Physics with RISING at GSI Nuclear Shell structure N = Z : 36 Ca to 100 Sn N>>Z : 56 Cr to 132 Sn Nuclear shapes Quadrupole, Octupole, Triaxiality High K-isomers Collective Modes N>>Z : GDR soft mode Nuclear Symmetries mirror-isospin, pn-pair correlation Nuclear Moments

253 RISING: Fast beam - physics focus Coulex in n-rich Cr isotopes Pigmy resonance in n-rich nuclei Coulex in nuclei towards 100 Sn Spectroscopy of mirror nuclei (A~50) via two-step fragmentation Coulex in triaxial nuclei 136 Nd Spectroscopy of 36Ca via two-step fragmentation Convener: P. Reiter, University of Cologne

254 Layout of the GSI facility SIS RISING FRS

255 Fragment Identification Tracking and Spectroscopy production selection identification reaction spectroscopy identification

Sn →Au Relativistic Coulomb excitation E = 100 MeV/u  L ≤ 3° I max ≈ 2  E max ≈ 10 MeV excited nucleus Coulomb interaction

Prefragment Equilibrated nucleus Fragmentation: v p >> v Fermi ; Impact parameter controls pre-fragment mass Abrasion: statistical process - single particle levels vacated - E* given by sum of hole energy above Fermi surface - I pre given by holes Ablation: statistical models - particle evaporation or fission - E* entry / I entry (similar to fusion) Nuclear Fragmentation Abrasion-ablation model ABRABLA

258 Secondary fragmentation –Be target –Suppression of the inelastic excitation of the projectile –Broad angular momentum distribution to high spins Coulomb excitation –Au target –One step excitation –Low spin Types of experiments

Ge crystals Energy resolution (FWHM): 1.24% Total efficiency: 2.9% [for E  = 1.3 MeV at 100 MeV/u] RISING In-flight set-up

2510 Hector Array time 142˚ 90˚ 84 Kr

2511 Atomic Background Radiation Atomic  background cross section To measure  - ray above ~ 300 keV Beam energy ~ 100 MeV/u X-rays from target atoms Radiative electron capture (REC) Primary Bremsstrahlung (PB) Secondary Bremsstrahlung (SB)

2512 Doppler Effect Doppler shiftDoppler broadening

2513 Scattering angle E  [keV] Counts 84 Kr (113 AMeV) + Au (0.4 g/cm 2 ) E  [keV] Counts Kr 2 +  0 + FWHM ~ 1.5 % pp   MW CATE SiCsI Target  reaction selection   -ray Doppler shift correction  atomic background suppression

2514 Coulomb Excitation of 108 Sn Shell model comparison: Core polarization multiple proton core particle-hole excitations A. Banu et al.

2515 Coulomb Excitation of n-rich Cr Isotopes Does a new sub-shell closure exist at N=32? Evidence for reduced B(E2) value at N=32 A. Bürger et al.

MeV/u 136 Nd→Pb Energy [keV] Coulomb excitation of 136 Nd First observation of second excited state at relativistic energies Evidence for  -soft triaxial behaviour GCM  =  = 24.2° (11) 11(3) 182 (93) T. Saito et al.

2517 Coulomb excitation of pygmy resonance in 68 Ni Contrib. O. Wieland PDR E = 11 MeV 5% EWSR

2518 Secondary fragmentation of 55 Ni on 9 Be at 140 MeV/u Mirror symmetry at N  Z (8 + ) Cr 46 Ti Ni Co Fe Mn Cr Ca Ti Ar S Si E dE First observation of higher spin states at relativistic energies extract lifetimes from lineshapes Mike Bentley et al.

2519 Isomeric ratios Zs. Podolyak et al. 148 Tb I = 27 + R = 3.2 (3) % Fragmentation of 208 Pb Fragmentation of 238 U Isomeric ratios I R [%] 211 Fr 29/ (2) 212 Fr (2) 213 Fr 29/ (8) 214 Ra (2) 215 Ra 43/ (6) Fragmentation populates high spin states

2520 High Spin enhancement in massive fragmentation Comparison with ABRABLA predictions 148 Tb I = 27 + R exp /  the = 23 - Sharp cut off limit - Yrast isomers Collective spin contribution

2521 High Spin enhancement in massive fragmentation Number of fragmented nucleons can not explain spin distribution! Collective effects add angular momentum to single particle spin Other effects??? Better description??? I (hbar) massive fragm.

2522 Experimental opportunites P ph : 3% → 8% (+16%)  E: 1.2% → 0.4% (5%) AGATA high-resolution  -tracking array LYCCA position sensitive  E/E/ToF detector array PARIS ??  -calorimeter

2523 Spectroscopy program at GSI / FAIR RISING 2007 – 2008 Decay with active stopper PRESPEC 2009 – 2010 In-beam employing LYCCA including ToF 2010 – 2011 Decay and g-factors 2011 – 2012 In-beam AGATA demonstrator together with Euroball detectors HISPEC/DESPEC 2013 – … In-beam and decay spectroscopy with Super-FRS at FAIR/NUSTAR

2524 Conclusions Coulomb and nuclear interactions at relativistic beam energies provide a universal method to populate excited states in nuclei Coulomb excitation populates low spin states from the first excited state up to giant resonances with a population pattern governed by B(E ) values Fragmentation reactions seem to populate low spin states unspecifically up to particle thresholds High spin states are populated in massive fragmentation reactions The underlying reaction mechanism is only qualitatively understood and more detailed investigations are required for a quantitative understanding Improved instrumentation is coming up soon… PRESPEC In-Beam Physics workshop, Daresbury October 2008

Some RISING collaborators

2526 … thank you

Ni →Au