ExperimentSpokesmanGoalRunning time Thesis? Scissors ModeTonchevAnalyze Scissors Mode excitations in actinide nuclei Pgymy DipoleTonchevAnalyze evolution of Pygmy Dipole resonance as a function of deformation 500 IVGQRAhmed, Weller Analyze IVGQR in A= nuclei evaluation resonance energy, width and EWSR – and compare with theory Structure Experiments – at 300 hrs are paid by DNDO

The Frontiers of Nuclear Science – A Long Range Plan (2007) [LRP, Nuclei: From Structure to Exploding Stars - What is the Origin of Simple Patterns in Nuclei, p 65] “ ”

2-phonon excitations: ⊗ 1-1- Found at sum energy of one-phonon states: ~ 3 MeV Found usually between MeV Proton-Neutron symmetric Existence because of nuclear 2-fluid system ⊗ 2 + FS 2 + MS 1+1+ Dipole Excitation Below 4 MeV: Scissors Mode Tonchev

Scissors mode systematics: clearly collective Degree of fragmentation depends on deformation Dipole Excitation Below 4 MeV

Proposed Experiments Where we are going: study the scissor mode in actinide nuclei 1. Completed experiments: 235 U, 238 U, 232 Th. 2. To be measured: 239 Pu, 237 Np, 233 U. 3. Working with the theorist to develop a model (RPA-based) to reproduce all experimental observables of the E1 and M1 excitations for actinides nuclei.

Interpretation of the Pygmy Resonance in QPM calculations Tonchev  PDR is predominantly E1 mode of excitation  PDR is enhanced strength below the GDR  We unveiled the fine structure of the M1 spin-flip mode  Evidence for surface neutron density oscillations  “Soft dipole mode“ at ~7 MeV is mixture of isoscalar and isovector components N. Tsoneva, H. Lenske, PRC 77, (2008), A.P. Tonchev et al. NIM B 241, (2005); A.P. Tonchev et al. AIP 819, 350 (2006); AIP 1090, 74 (2009); A.P. Tonchev et al. PRL (2010). pn  What we have learned ?

Fine and Gross Structure of the PDR in 138 Ba A. Tonchev et al., PRL 104, (2010) Fine structureGross structure

Pygmy Dipole Resonance Impact Nuclear astrophysics: r-process 1998 S. Goriely PLB 2003 M. Arnold et al. PR 2005 T. Rauscher NPA Neutrino-less double-beta decay physics 2004 J. Bahcall et al. PRD Extract the γ-ray transition matrix elements for the decay (QRPA)‏ Study of the structure difference of the initial and final states Study of the nuclear dipole response in 76 Se and 76 Ge isotopes Testing the nuclear models for stable and extrapolating to exotic nuclei 1998 S. Goriely, PLB; 2008 G. Rusev,PRC Neutron radius: PDR provides experimental constrains on properties of nuclear matter (neutron skin and symmetry energy) 2006 Piekarewicz PRC

124 Xe Present Experimental Activity with N=82 Nuclei 130 Xe Z=54 N= Ba 140 Ce 142 Nd 144 Sm Completed measurements at HIGS p,nn N/Z Sm  Proposed measurements 136 Xe 132 Xe Predicted dependence on N/Z ratio  weak isospin effect 134 Xe B(E1) [10 -3 e 2 fm 2 ]

Proposed Experiment 1.PDR as a function of deformation Sm 62 N/Z ↑  ↑ Increased deformation with N/Z Xe 54 N/Z ↑  ↓ Decreased deformation with N/Z F. Dönau et. al. PRC 76, (2007); G. Rusev et al. PRC 73, (2006); G. Rusev et al., PRC (2009) QRPA calculations N PDR region

An example – 209 Bi IVGQR odd ± (E) Weller, Ahmed

209 Bi Results

209 Bi Results – Notice Quality of Our data