Complete Dipole Strength Distributions from High -Resolution Polarized Proton Scattering at 0° Peter von Neumann-Cosel Institut für Kernphysik, Technische Universität Darmstadt § Complete electric dipole strength distributions - what can be learned § High-resolution polarized proton scattering as a spectroscopic tool § The case of 208 Pb SFB 634 *Supported by the DFG within SFB 634 and 446 JAP 113/267/0 -2 Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 1
Complete Dipole Strength: What can be Learned? § Pygmy dipole resonance (PDR) Test of microscopic models § Dipole polarizability Neutron skin and symmetry energy § Level densities Test of Hauser-Feshbach approach in large-scale reaction network calculations § Photon strength function Test of Axel-Brink hypothesis Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 2
Pygmy Dipole Resonance § Soft E 1 mode due to oscillation of neutron skin vs. approximately isospin-saturated core § PDR strength related to neutron skin § Neutron skin related to neutron-matter EOS J. Piekarewicz, PRC 73 (2006) 044325. S. Typel, B. A. Brown, PRC 64 (2001) 027302 Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 3
Polarizability § Static nuclear dipole polarizability § αD is measure of neutron skin P. G. Reinhard, W. Nazarewicz, PRC 81 (2010) 051303 (R) J. Piekarewicz, ar. Xiv: 1012. 1803 Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 4
Hauser-Feshbach calculations § Statistical model approach to reaction cross sections in astrophyiscal large-scale network calculations § Required input - Photon strength function - Level densities - Axel-Brink hypothesis (thermal population of excited states) Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 5
Photon Strength Function (PSF) Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel 6
Axel-Brink Hypothesis § Strength - depends only on Eg - is independent of the initial state structure: Ex, Jp, … § Same PSF for γ absorption and emission Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 7
Influence of the PDR E. Litvinova, Workshop on Gamma Strength and Level Density, Dresden-Rossendorf, August 2010 E. Litvinova et al. , NPA 823 (2009) 26 Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 8
Experimental Discrepances in PSF ? Ann-Cecilie Larsen, Workshop on Gamma Strength and Level Density, Dresden-Rossendorf, August 2010 Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 9
Problems G. Rusev et al. , PRC 79 (2009) 061302 Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 10
Problems (continued) § (g, xn) reactions provide information above threshold only and little sensitivity close to threshold § Decay of compound nuclei → normalization at Sn → level densities needed Consistent data on E 1 strength below and above the neutron threshold highly important Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 11
A New Experimental Tool for Complete Dipole Strength Distributions § Polarized proton scattering at 0 o - intermediate energy: 300 Me. V optimal for spin/isospin excitations - Coulomb excitation of 1 - states - high resolution: ΔE = 25 ke. V (FWHM) - angular distributions: E 1 / M 1 separation - polarization observables: spinflip / non-spinflip separation § 208 Pb as a reference case Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 12
0 o Setup at RCNP Measured observables ds/d. W - angular distributions (0° ≤ Q ≤ 10°) Ay - asymmetry DSS at 0° - sideways polarization DLL at 0° - longitudinal polarization A. Tamii et al. , NIMA 605 (2009) 326 Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 13
Measured Spectrum ΔE = 25 ke. V (FWHM) Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 14
Measured Spectrum: Low-Energy Part § All dipole transitions known from (g, g´) are observed Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 15
E 1/M 1 Decomposition by Spin Observables T. Suzuki, PTP 103 (2000) 859 Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 16
Decomposition into Spinflip / Non-Spinflip Cross Sections Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 17
Multipole Decomposition of Angular Distributions Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 18
Comparison of Both Methods Total DS = 1 DS = 0 Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 19
B(E 1) Strength: Low-Energy Region Ec = 7. 30 ± 0. 03 Me. V Ec = 7. 43 ± 0. 02 Me. V § Extracted assuming semiclassical Coulomb excitation Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 20
B(E 1) Strength: GDR Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 21
E 1 Response in 208 Pb: Experiment vs. Theory V. Yu. Ponomarev 3 p 3 h (Ex ≤ 10 Me. V), 2 p 2 h for GDR N. Ryezayeva et al. , PRL 89 (2002) 272502 E. Litvinova 1 p 1 h phonon E. Litvinova et al. , PRC 78 (2008) 014312, PRC 79 (2009) 054312 Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 22
Polarizability and neutron skin § Precision value: αD(208 Pb) = 19. 98(58) fm 3/e 2 = 13. 88(41) fm 2/Me. V § Within the model of P. G. Reinhard and W. Nazarewicz, PRC 81 (2010) 051303 rskin = 0. 155(23) fm § Combined with model-independent measurement of rskin by PREX true constraint for isovector properties of any microscopic interaction Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 23
Level densities § Extracted from a fluctuation analysis of the fine structure of the GDR S. Müller, F. Beck, D. Meuer, and A. Richter, PLB 113 (1982) 362 P. G. Hansen, B. Jonson, and A. Richter, NPA 518 (1990) 13 § Depends on the background determined from - multipole decomposition analysis - discrete wavelet analysis of the spectrum Y. Kalmykov et al. , PRL 96 (2006) 012502 Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 24
1 - states level densities in 208 Pb Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 25
Photon Strength Function in 208 Pb N. U. H. Syed et al. , PRC 79 (2009) 024316 Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 26
Summary and Outlook § Polarized intermediate energy proton scattering at 0°: a new tool to extract the complete dipole response in nuclei - Spinflip / non-spinflip cross section separation - B(E 1) strength - Dipole polarizability - Level Densities of 1 - states - Photon Strength Function § Experiment on 120 Sn: extraction of complete PDR strength § Experiment on 154 Sm: PDR in a heavy deformed nucleus Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 27
First 0° Proton Scattering Experiments at i. Themba LABS, South Africa U Cape Town / TU Darmstadt / i. Themba LABS / U Osaka / RCNP Osaka / U Witwatersrand collaboration R. Neveling et al. , NIMA (submitted) Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 28
Collaboration Dep. of Phys. , Kyoto University H. Sakaguchi, J. Zenihiro RCNP, Osaka University T. Adachi, H. Fujita, K. Hatanaka, M. Kato, H. Matsubara, M. Okamura, Y. Sakemi, Y. Shimizu, Y. Tameshige, A. Tamii, M. Yosoi CNS, Univ. of Tokyo Y. Sasamoto i. Themba LABS R. Neveling, F. D. Smit IFIC-CSIC, Valencia B. Rubio Texas A&M University, Commerce, USA C. Bertulani Dep. of Phys. , Osaka University Y. Fujita Univ. of Witwatersrand J. Carter GSI, Darmstadt B. Özel, E. Litvinova IKP, TU Darmstadt A. M. Heilmann, Y. Kalmykov, P. von Neumann-Cosel, I. Poltoratska, V. Yu. Ponomarev, A. Richter, J. Wambach Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 29
Multipole Decomposition of Angular §Distributions Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel 30
Coulomb Exitations of 1 - States Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel 31
Fluctuation Analysis § Background from MDA § Stationary spectrum g(Ex) g>(Ex) § Autocorrelation function Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel 32
Autocorrelation Function and Mean Level Spacing § autocorrelation function § variance § level spacing D § statistical properties § resolution Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel 33
Wavelets § Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel 34
DWT of 208 Pb spectrum Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel 35
Multipole Decomposition in the GDR Region - identical angular distributions - determines phenomenological background Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 36
Comparison of Both Methods II Total DS = 1 DS = 0 Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 37
Spinflip M 1 Strength § Isovector part: analog of GT modes with T = T 0 § Spinflip M 1 resonance is quenched - in fp-shell nuclei similar to GT strength - in heavy nuclei – little data → 208 Pb as a test case § Problem studied in the 80’s but: - large experimental uncertainties - improved model calculations § new experimental access by (p, p´) - intermediate energy region optimal for spin-isospin excitations - at 0° → selectivity on DL=0 transitions - isovector spinflip M 1 transitions enhanced Peter von Neumann-Cosel | Nuclear Physics in Astrophysics, April 3 -8, 2011, Eilat, Israel | Institut für Kernphysik | TU Darmstadt | P. von Neumann-Cosel 38
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