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

Introduction Experimental Setup Analysis and Results Comparison with Theory Summary

Darmstadt University of Technology Institute for Nuclear Physics

S-DALINAC

Layout of the S-DALINAC

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

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) S. P. Kamerdizhiev, S. F. Kovaloo, PAN 65 (2006) 418 J. Terasaki, J. Engel, PRC 74 (2006) E. Litvinova et al., PLB 647 (2007) 111 Darmstadt GSI Nuclear Resonance Fluorescence Gent Coulomb Dissociation

Real photon experiments at the S-DALINAC

NRF Setup

Spectra

Angular Distribution 90  130  =1 =2

Photon Flux

Photon Flux with 11 B

Extracted B(E1) Strengths 174 (26) 165 (34)  B(E1) e 2 fm 2

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

Comparison with Theory: Fragmentation

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

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

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) BSFG2 P. Demetriou and S. Goriely, NPA 695 (2001) 95 HF-BCS

Unresolved Strength in the Background PRELIMINARY

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

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