Institut für Theoretische Physik, Universität Giessen LOW-ENERGY MULTIPOLE EXCITATIONS AND NUCLEOSYNTHESIS Nadia Tsoneva INTERNATIONAL SCHOOL OF NUCLEAR PHYSICS 36th Course Nuclei in the Laboratory and in the Cosmos Erice-Sicily: September 16-24, 2014

R. Schwengner, F. Donau, S. Frauendorf, E. Grosse Triangle Universities Nuclear Laboratory, Durham, USA W. Tornow, A.P. Tonchev, G. Rusev et al. Monash Centre for Astrophysics (MoCA), Australia M. Lugaro P. von Neumann-Cosel, N. Pietralla, A. Richter, D. Savran S. Goriely Institute of Astronomy and Astrophysics (IAA) Université libre de Bruxelles, Belgium A. Zilges, V. Derya, M. Spieker et al. Horst Lenske N.Tsoneva, ERICE14

Nucleosynthesis of Heavier Elements Heavier elements ( Z> 26-28) can be assembled within stars by neutron capture processes. Two main neutron capture processes s- process – slow neutron capture, low neutron densities  ~ 10 8 /cm 3 life time  ~ 1 – 10 years r – process - rapid neutron captures  ~ /cm 3 …other processes Fusion in stars s-process ? r-process p-process N.Tsoneva, ERICE14

Characteristic Response of an Atomic Nucleus to EM Radiation Scissors mode Two-phonon excitation Pygmy-quadrupole resonance Pygmy-dipole resonance Spin-flip M1 Giant M1 resonance Giant Dipole Resonance E1 (GDR) E (MeV) Theoretical prediction of Pygmy Quadrupole Resonance: N. Tsoneva, H. Lenske, Phys. Lett. B 695 (2011) 174. N.Tsoneva, ERICE14

The Theoretical Model N. Tsoneva, H. Lenske, Ch. Stoyanov, Phys. Lett. B 586 (2004) 213 N. Tsoneva, H. Lenske, Phys. Rev. C 77 (2008) Nuclear Ground State Single-Particle States Phenomenological density functional approach based on a fully microscopic self-consistent Skyrme Hartree-Fock-Bogoljubov (HFB) theory Pairing and Quasiparticle States Excited states deformations, vibrations, rotations H M ph - multipole interaction in the particle-hole channel; H SM ph - spin-multipole interaction in the particle-hole channel; H M pp - multipole interaction in the particle-particle channel Quasiparticle-Phonon Model: V. G. Soloviev: Theory of Atomic Nuclei: Quasiparticles and Phonons ( Bristol, 1992) isoscalar interaction isovector interaction N.Tsoneva, ERICE14

Phenomenological Density Functional Approach for Nuclear Ground States P. Hohenberg, W. Kohn, Phys. Rev. 136 (1964) B864; W. Kohn, L. J. Sham, Phys. Rev. 140 (1965) A N. Tsoneva, H. Lenske, PRC 77 (2008) The total binding energy B(A) is expressed as an integral over an energy-density functional  q,  q, k q – number, kinetic and pairing density effective potential neutron skin thickness Z=50 N.Tsoneva, ERICE14

The thickness of the neutron skin scaled with the difference of the Fermi levels of the protons and neutrons  F corrected for the Coulomb barrier. S 2p, S 2n – two proton (neutron) separation energies, E C – the height of the Coulomb barrier at the nuclear radius (CCF=Coulomb Corrected Fermi energy) a measure of how loosely the neutrons are bound compared to the protons. NeutronsProtons FnFn FpFp Even-Even Neutron-Rich Nucleus  F E 0 r V c (r)~Ze 2 /rEcEc E Sn 108 Sn 124 Sn 116 Sn 132 Sn N.Tsoneva, ERICE14

N. Tsoneva, H. Lenske, Phys. Rev. C 77 (2008) R. Schwengner et al., Phys. Rev. C 78 (2008) Calculations of Ground State Densities in Z=50, N=50,82 Nuclei Radius [fm] N.Tsoneva, ERICE14

Theory of Nuclear Excitations The QPM basis is built of phonons: The phonons are not ‘pure‘ bosons: Pauli principle QRPA equations are solved: fermionic corrections ~ labels the number of the QRPA state Quasiparticle-Phonon Model: V. G. Soloviev: Theory of Atomic Nuclei: Quasiparticles and Phonons ( Bristol, 1992) N.Tsoneva, ERICE14

Anharmonicities in Nuclear Wave Function M. Grinberg, Ch. Stoyanov, Nucl. Phys. A. 573 (1994) 231 For even-even nucleus the QPM wave functions are a mixture of one-, two- and three-phonon components one-phonon part two-phonon part three-phonon part N.Tsoneva, ERICE14

U. Kneissl, N. Pietralla, and A. Zilges, J. Phys. G: Nucl.Part.Phys. 32, R217 (2006) Two-Phonon Quadrupole-Octupole 1 - states stable and unstable Sn nuclei Excitation probability of the state from the ground state Excitation probability of the state from the ground state Excitation probability of the state from the ground state E1 transition probability of the state to the state N. Tsoneva, H. Lenske, Ch. Stoyanov, Phys. Lett. B 586 (2004) 213 N.Tsoneva, ERICE14

Pygmy Dipole Resonance in Sn Isotopes PDR GDR PDR GDR PDR GDR N. Tsoneva, H. Lenske, PRC 77 (2008) Radius [fm ] Transition densities are related to nuclear transition strengths N>Z N=Z N.Tsoneva, ERICE14

Neutron number increasing Neutron skin increasing A connection between PDR strengths and neutron skins N. Tsoneva, H. Lenske, PRC 77 (2008) Pygmy Dipole Resonance and the Dynamics of Nuclear Skin Similar observations found also in N=50, 82 isotones ! N.Tsoneva, CGS15

Multiphonon Calculations of E1 Transitions in 112,120 Sn N/Z( 112 Sn)= 1.24 N/Z( 120 Sn)= 1.4 GDR (E*>8MeV) (1ph) PDR (1ph+2ph+3ph) PDR submitted to PRC N.Tsoneva, ERICE14

Dynamics of Neutron Skin Oscillations in N=50 Isotones exp : R. Schwengner et al., First systematic photon-scattering experiments in N=50 nuclei: using bremsstrahlung produced with electron beams at the linear accelerator ELBE, Rossendorf and quasi-monoenergetic  – rays at HI  S facility, Duke university. N.Tsoneva, ERICE14

R. Raut,…,N.Tsoneva et al., Phys. Rev. Lett. 111, (2013). Total cross section of 85 Kr g (n,  ) 86 Kr reaction A way to investigate 85 Kr branching point and the s-process: 85 Kr (  ~ Y) ground state is a branching point and thus a bridge for the production of 86 Kr at low neutron densities. N.Tsoneva, ERICE14 QRPA, QPM calculations by N. Tsoneva TALYS calculations by S. Goriely

Population of 86 Kr in n-capture reactions related to s- and r-processes of the nucleosynthesis s-processr-process N.Tsoneva, ERICE14

N. Tsoneva, H. Lenske, Phys. Lett. B 695 (2011) 174 Theoretical Prediction of Pygmy Quadrupole Resonance ISGQR PQR PQR – pygmy quadrupole resonance ISGQR – isoscalar giant quadrupole resonance IVGQR – isovector giant quadrupole resonance PQR ISGQR IVGQR I=0 I=1 I=0 I=1 PQR strength increases with the neutron number: B(E2) ~ 1/  n b 2 N.Tsoneva, ERICE14

M. Spieker, J. Endres, A. Zilges, Universität zu Köln QPM calculations in comparison with data ( ,  ‘) N.Tsoneva, CGS15

Parity Measurements with Polarized Photon Beams of Low-energy Dipole Excitations at HI  S, Duke University A. Tonchev…N. Tsoneva, et al., Phys. Rev. Lett. 104, (2010) 138 Ba   (M1)/   (E1) ~ 3% First systematic spin and parity measurements in comparison with QPM calculations: 138 Ba verified for the first time that the pygmy dipole resonance is predominantly electric dipole in nature. The fine structure of the M1 spin-flip mode is explained. Separation of the PDR to isoscalar and isovector. Interplay between the GDR and the PDR at higher energies. N.Tsoneva, CGS15

Fine Structure of the Giant M1 Resonance in 90 Zr G. Rusev, N. Tsoneva, F. Dönau, S. Frauendorf, R. Schwengner, A. P. Tonchev, A. S. Adekola, S. L. Hammond, J. H. Kelley, E. Kwan, H. Lenske, W. Tornow, and A. Wagner, Phys. Rev. Lett. 110, (2013). Explaining the fragmentation pattern and the dynamics of the ‘quenching’. Multi-particle multi-hole effects increase strongly the orbital part of the magnetic moment. Prediction of M1 strength at and above the neutron threshold.  B(M1) Exp. = 4.5 (6)  N 2  B(M1) QPM. = 4.6  N 2 E c.m. Exp. = 9.0 MeVE c.m. QPM = 9.1 MeV Precision data on M1 strength distributions are of fundamental importance g s eff =0.8 g s bare Spin and Parity Determination at HI  S, Duke University, USA N.Tsoneva, ERICE14

A theoretical method based on Density Functional Theory and Quasiparticle-Phonon Model is developed. Presently, this is the only existing method allowing for sufficiently large configuration space such that a unified description of low-energy single-particle, multiple-phonon states and the giant resonances is feasible. Different applications of the method are presented: - systematic studies of low energy dipole strengths reveal new mode of nuclear excitation - Pygmy Dipole Resonance as a unique mode of excitation correlated with the size of the neutron skin. - theoretical prediction of a higher order multipole pygmy resonance – Pygmy Quadrupole Resonance. - description of the fragmentation pattern of E1, E2 and M1 strengths - nuclear structure input for astrophysics Conclusions N.Tsoneva, ERICE14

First Systematic Studies of the PDR in N=50 Isotones R. Schwengner,…, N.Tsoneva et al, Phys. Rev. C 87, (2013) Experiment: bremsstrahlung produced with electron beams at the linear accelerator ELBE and quasi-monoenergetic  – rays at HI  S facility at Duke university. N.Tsoneva, LANZHOU14

Cross-Section measurements of the 86 Kr( ,n) Reaction to Probe the S-Process Branching at 85 Kr R. Schwengner… N. Tsoneva et al., Phys. Rev. C 87, (2013); R. Raut…N. Tsoneva et al., Phys. Rev. Lett. 111, (2013). Lorentz strength function ( ,  ‘) data 86 Kr QRPA N.Tsoneva, LANZHOU14

QRPA CALCULATIONS OF PQR STATES IN SN ISOTOPES N. Tsoneva and H. Lenske, Phys. Lett. B 695 (2011) 174 B(M1; 2 i ) ~  N 2 Pygmy Quadrupole Resonance is a genuine mode B(E2) ~ 1/  n b 2 g 9/2 - a proton Fermi level;  p b = MeV in 134 Sn ;  p b =-7.20 MeV in 104 Sn B(E2) increases with the neutron number N N.Tsoneva, CGS15