Norbert Pietralla Isolde WS2007 Nuclear Mixed-Symmetry States as Probe for pn Effective Valence Shell Interaction Institut für Kernphysik, TU-Darmstadt Mixed Symmetry States Recent Progress Research with RIBs Outlook & Summary Outline Christoph Fransen Georgi Rainovski Jason Holt Nico Orce Oleksiy Burda Peter von Neumann-Cosel Volker Werner Tan Ahn ANL Collaborators Norbert Pietralla CRE Nuclear/Radiation physics SFB634 S-DALINAC, TUD

Norbert Pietralla Isolde WS2007 Heavy Atomic nucleus many-body system consists of two equivalent entities (protons-neutrons) quantum system COLLECTIVITY ISOSPIN SYMMETRY SHELL STRUCTURE Two-fluid quantum system Generic Aspects of Nuclear Structure Coexist, interplay, and compete? Study collective isovector valence shell excitations (combine all 3 aspects) Study mixed symmetry (MS) structures !

Norbert Pietralla Isolde WS2007 Model pn-symmetry in valence shell F-spin = Isospin in Systems of “elementary” Bosons Approximation: IBM, analytic solutions Contain pn-antisymmetric boson pairs Signature: enhanced M1 radiation

Norbert Pietralla Isolde WS2007 Simple Example: Harmonic Oscillator, N=2 E 2+n2+n ms 2+p2+p V pn

Norbert Pietralla Isolde WS2007 Experimental signature for MSSs: M1 transitions g   1  N, g  0  N M1 forbidden between FSSs! LL L

Norbert Pietralla Isolde WS2007 Richter, Kneissl, von Brentano et al. Sensitivity to Shell Structure MSSs at the analytical Limits N  = N =1 Status of MS structures in vibrational nuclei M1 phenomena in the valence shell E2M1 Scissors mode Measure of quadrupole collectivity SU(3) Rotor Scissors Mode A. Richter et al. TU Darmstadt, 1983 K=1 Stuttgart-Darmstadt-Köln U(5) Vibrator F max -1 MS multi-Phonon structure N. Pietralla et al., PRC 58, 184 (1998)

Norbert Pietralla Isolde WS2007 Mixed symmetry phonon structure at N = Nb Orce et. al (2006)

Norbert Pietralla Isolde WS2007 Identification of multi-phonon MSSs M1 strength, E2 strength from g.s.

Norbert Pietralla Isolde WS2007 First observation of vibrational MS structure in odd-mass nuclei J.N. Orce et al, PRL 97, (2006). 93 Nb 94 Mo B(M1) 93Nb = 0.32(11)[0.62(24)]  N 2 B(M1) 94Mo = 0.56(5)  N ms Doppler-shift lifetimes from (n,n‘  ) at Lexington

Norbert Pietralla Isolde WS2007 Systematic SM calculations from NN interaction with V low-k J. D. Holt et al, (submitted) Yale-Rutgers collaboration (preliminary) x Inverse kinematics Coulomb excitation

Norbert Pietralla Isolde WS2007 Program at S-DALINAC M1/g-factor = integral  one value Cross sections = differential  a function (1-dim more structure information) Electron Spectrometer 130 MeV in-house electron LINAC ideal for nuclear structure studies

Norbert Pietralla Isolde WS2007 Program at S-DALINAC M1/g-factor = integral  one value Cross sections = differential  a function (1-dim more structure information) Electron Spectrometer 130 MeV in-house electron LINAC ideal for nuclear structure studies

Norbert Pietralla Isolde WS2007 Electron scattering on vibrational multi-phonon MSSs 94 Mo(e,e’) Ideal for one-phonon states Sensitive to 14 lowest 2 + states 94 Mo(p,p’) iThembaLabs data with H.Fujita P.von Neumann-Cosel et al. Darmstadt data with O.Burda, P.von Neumann-Cosel A.Richter et al.

Norbert Pietralla Isolde WS Mo(e,e’) Form Factors Test of quantum mechanical wavefunction IBM-2 and SM V low-k in good agreement with experiment. combination with hadronic probe [forward-angle (p,p’) at iThembaLabs] allows for isospin-sensitivity. Experiment QPM IBM-2 SM (V low-k )

Norbert Pietralla Isolde WS2007 Inverse kinematics CoulEx to MSSs at ANL carbon G.Rainovski, NP et al, PRL (2006) 138 Ce Coulomb excitation Detector array Study pn-symmetry in valence shell REX-Isolde, HRIBF, CARIBU,… exotic nuclei (2 + 1 →0 + ) 1448 (2 + ms →2 + 1 ) 2237 (2 + ms →0 + 1 ) M1 E2 gs 2 + ms

Norbert Pietralla Isolde WS2007 CoulEx of Mixed-Symmetry States Observe 2+ 1,2,3,4,5,6 up to 2.7 MeV G.Rainovski, NP et al., Phys.Rev.Lett (2006). Gammasphere at ANL in collaboration M.P.Carpenter R.V.F.Janssens C.J.Lister S.Zhu 2 + ms

Norbert Pietralla Isolde WS2007  = 1.204(33)ps  = 180(9)fs  = 82(5)fs  = 156(10)fs  = 91(36)fs The population cross-sections at 480 MeV CLX code (H. Ower – J. Gerl – H. Scheit) Based on Multiple step Coulex theory (Winter – de Boer) B(E2, )↑= 0.450(30) e 2 b 2 B( , J j + )  BR CLX + Radiation character from angular distribution

Norbert Pietralla Isolde WS2007 Transition Strength Distributions E2 M1 E2

Norbert Pietralla Isolde WS2007 Two-Level Mixing  2 = B(M1;2 + 4  )/ B(M1;tot) = 0.12/0.18 = 0.7 V F-mix = 44(3) keV => “shell stabilization of MS structures”

Norbert Pietralla Isolde WS2007 MSS Argonne (“Missia”) program overview ANL ATLAS Superconducting LINAC Gammasphere Published Under analysis Expt accepted proposed Xe Ce Ba Sm Chart from: Previous literature

Norbert Pietralla Isolde WS2007 Recent Coulex Experiments November 2005 at ANL: 136 Ce, 134 Xe June 2006 at ANL: 124,126,128,130,132 Xe (under analysis) 134 Xe 2 + ms 132 Xe 2 + ms

Norbert Pietralla Isolde WS2007 Direct evidence for p-n interaction V pn in the valence shell Energy splitting increases with growing valence shell (increasing N p ) Task for Radioactive Beam Accelerators (e.g. HRIBF, REXIsolde…) Proton Number Z One phonon 2 + evolution in N=80 isotones Te 2 + ms V pn ~ (N p N n ) 1/2 E 2+n2+n ms 2+p2+p V pn

Norbert Pietralla Isolde WS2007 What RIB intensity needed for studying MSSs? 15 h at pps! 1/25 1/250 1/ pps for 2 weeks 10 6 pps for 2 weeks 10 5 pps for 2 weeks To identify excited 2 + state (beyond the ) in vibrational nucleus (B(E2)~1Wu) with Gammasphere for 2 weeks beam time we need 10 5 pps. For complete spectroscopy pps will be needed! 2 + ms

Norbert Pietralla Isolde WS2007 Outlook (e,e’)  transition densities for p and n Trace evolution of V p-n RIBS  exotic nuclei  HRIBF, ANL CARIBU, REX-ISOLDE, SPIRAL II, … Proton Number Z ms 2 + evolution in N=80 isotones 132 Te 140 Xe Xe 2 + FWHM ~9 keV R. Kruecken et al. Munich (2006) CERN REX-ISOLDE part/sec

Norbert Pietralla Isolde WS2007 Proton-Neutron Mixed-Symmetry States are sensitive probes of the pn-interaction in the valence shell 94 Mo – a textbook example 93 Nb – first vibrational MSSs in odd-A nucleus Advances in nuclear theory (V low-k for MS) First g-factors for MSSs ( 92,94 Zr) New avenue in S-DALINAC “Missia” ANL Great potential for RIBs (map V pn in exotic regions) Summary