1. Dipole Strengths in 112,120 Sn and Systematics of the Pygmy Dipole Resonance at Z=50 Shell Closure BANU ÖZEL 1,2, J. ENDERS 1, Y. KALMYKOV 1, P. von NEUMANN-COSEL 1, A. RICHTER 1, D. SAVRAN 1 and A. ZILGES 1 1 Institut für Kernphysics, Tecnische Universität Darmstadt, Germany 2 Cukurova University, Turkey TECNISCHE UNIVERSITÄT DARMSTADT RCNP OSAKA

2. Introduction Experimental Setup Analysis and Results Comparison with Theory Summary

3. Darmstadt University of Technology Institute for Nuclear Physics

4. S-DALINAC

5. Layout of the S-DALINAC

6. Pygmy Dipole Resonance Giant Dipole Resonance neutron skin N≈Z core neutron proton Two Phonon State x Dipole excitations in nuclei

7. 112Sn STABLE 0.97% 120Sn STABLE 32.58% 116Sn STABLE 14.54% 124Sn STABLE 5.79% 130Sn 3.72 M  - 132Sn 39.7 S  - Systematics of the PDR in the Sn Isotope Chain There are many theoretical calculations Experimental data in stable and unstable Sn isotopes available N. Tsoneva et al., NPA 731 (2004) 273 D. Sardi et al., PLB 601 (2004) 27 N. Paar et al., PLB 606 (2005) 288 J. Piekarewicz, PRC 73 (2006) 044325 S. P. Kamerdizhiev, S. F. Kovaloo, PAN 65 (2006) 418 J. Terasaki, J. Engel, PRC 74 (2006) 044325 E. Litvinova et al., PLB 647 (2007) 111 Darmstadt GSI Nuclear Resonance Fluorescence Gent Coulomb Dissociation

8. Real photon experiments at the S-DALINAC

9. NRF Setup

10. Spectra

11. Angular Distribution 90  130  =1 =2

12. Photon Flux

13. Photon Flux with 11 B

14. Extracted B(E1) Strengths 174 (26) 165 (34)  B(E1) 10 -3 e 2 fm 2

15. E1 Strength Distributions in Stable Sn Isotopes  B(E1) 10 -3 e 2 fm 2 174(26) 233 (28) 165 (34) 379 (43)

16. Comparison with Theory: Fragmentation

17. Comparion with Theory: Centroid and Cumulative Strength Note: ( ,  ´)measures strength below threshold only Coulomb dissociationmeasures strength above threshold only

18. Comparison with Theory: Cumulative Strengths No simple dependence on neutron excess (or N/Z ratio)

19. Unresolved Strength in the Background Is there unresolved strength in background? Fluctuation Analysis J. Enders et al., PRL 79 (1997) 2010 Applicable in region where  D  >  E Level density from models T. Rauscher et al., PRC 56 (1997) 1613 BSFG1 T. von Egidy and D. Bucurescu, PRC 72 (2005) 044311 BSFG2 P. Demetriou and S. Goriely, NPA 695 (2001) 95 HF-BCS

20. Unresolved Strength in the Background PRELIMINARY

21. Summary Systematic of PDR in stable Sn isotopes established Models close to results either in stable or in unstable nuclei, but not both No simple dependence of total strength on neutron excess We need measurements across the neutron threshold - NEPTUN tagger at S-DALINAC - High resolution (p,p´) at 0 o at RCNP

22. Thanks TU Darmstadt U. of Giessen A. Richter, P. von Neumann-Cosel, J. Enders, Y. Kalmykov, V. Ponomarev, I. Poltoratska D. Savran, A. Zilges H. Lenske, N.Tsoneva, N. Paar, J. Piekarewicz, Florida SU U. of Zagreb Thanks to RCNP and Prof. Dr. Atsushi Tamii