Structure Experiments – at HIGS

1. Structure Experiments – at HIGS @ 300 hrsare paid by DNDO

2. 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] ”

3. ⊗ 2+FS 2+MS 1+ Dipole Excitation Below 4 MeV: Scissors Mode Tonchev 2-phonon excitations: ⊗ 1- Found at sum energy of one-phonon states: ~ 3 MeV Found usually between 2.7-3.6 MeV Existence because of nuclear 2-fluid system Proton-Neutron symmetric

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

5. Proposed Experiments Where we are going: study the scissor mode in actinide nuclei 1. Completed experiments: 235U, 238U, 232Th. 2. To be measured: 239Pu, 237Np, 233U. 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.

6. Interpretation of the Pygmy Resonance in QPM calculationsTonchev  p n What we have learned ? • 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, 024321 (2008), A.P. Tonchev et al. NIM B 241, 51474 (2005); A.P. Tonchev et al. AIP 819, 350 (2006); AIP 1090, 74 (2009); A.P. Tonchev et al. PRL 104 072501 (2010).

7. Fine and Gross Structure of the PDR in 138Ba Fine structure Gross structure A. Tonchev et al., PRL 104, 072501 (2010)

8. 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 76Se and 76Ge isotopes • Neutron radius: PDR provides experimental constrains on properties of nuclear matter (neutron skin and symmetry energy) 2006 Piekarewicz PRC Testing the nuclear models for stable and extrapolating to exotic nuclei • 1998 S. Goriely, PLB; 2008 G. Rusev ,PRC

9. Present Experimental Activity with N=82 Nuclei 2 0.09 0.10 0.09 0.09 B(E1) [10-3e2fm2] 536 576 600 960 N/Z 1.32 1.37 1.41 1.46 144Sm 154Sm 154Sm 142Nd 140Ce 138Ba 124Xe 130Xe Z=54 132Xe 136Xe 134Xe N=82 Completed measurements at HIGS Proposed measurements p,n n • Predicted dependence on N/Z ratio  weak isospin effect

10. Proposed Experiment QRPA calculations PDR as a function of deformation 144 148 152 154Sm62 N/Z 1.32 1.39 1.45 1.48 ↑ 20.09 0.14 0.31 0.34 ↑ Increased deformation with N/Z 128 130 132 134 136Xe54 N/Z 1.37 1.41 1.44 1.48 1.52 ↑ 20.18 0.17 0.14 0.12 0.09 ↓ Decreased deformation with N/Z N PDR region F. Dönau et. al. PRC 76, 014317 (2007); G. Rusev et al. PRC 73, 044308 (2006); G. Rusev et al., PRC (2009)

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

12. 209Bi Results

13. 209Bi Results – Notice Quality of Our data

14. 209Bi Results – Notice Quality of Our data