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Systematic Study of PDR, GDR and GQR for the Chain of Tin Isotopes

Systematic Study of PDR, GDR and GQR for the Chain of Tin Isotopes. s412 experiment Spokespeople: T. Aumann and K. Boretzky R 3 B-EXL-ELISe Joint Collaboration Meeting on Technical Issues 15.04.2010. D. Rossi. Measurement of Pygmy Dipole Resonances.

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Systematic Study of PDR, GDR and GQR for the Chain of Tin Isotopes

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  1. Systematic Study of PDR, GDR and GQR for the Chain of Tin Isotopes s412 experiment Spokespeople: T. Aumann and K. Boretzky R3B-EXL-ELISe Joint Collaboration Meeting on Technical Issues15.04.2010 D. Rossi

  2. Measurement of Pygmy Dipole Resonances Pygmy Dipole Resonances (PDR) have been observed previously in Sn isotopes at LAND Overlap of PDR and GDR strength at low energies due to detector response Staggered PDR distributions in odd / even isotopes PDR strength distribution below or above neutron threshold, or varies with threshold? A. Klimkiewicz et al., Phys. Rev. C 76, 051603(R) (2007) P. Adrich et al., PRL 95, 132501 (2005) D. Rossi

  3. Measurement of Pygmy Dipole Resonances PDR measurement in 68Ni @ 600 AMeV using virtual photon scattering Method allows measurement below and above neutron threshold PDR strength has been measured above neutron threshold 68Ni (g,g’) O. Wieland et al., PRL 102, 092502 (2009) D. Rossi

  4. Experiment Overview Aims of proposed experiment: Systematic investigation of E1 strength in Sn isotopic chain from A = 124 to 134 PDR measurement below and above the neutron threshold Measurement of E2 strength in 124Sn to 128Sn Excitation with isoscalar probe (CD2 target) Improvements compared to previous experiments Better mass resolution Improved detector response Better statistics D. Rossi

  5. Aim of Proposed Experiment • Measurement of isovector GDR in complete Sn isotopic chain from A = 124 to 134 with high statistics • Reduce statistical error for the systematical extraction of GDR parameters • Observation of direct photon-decay of GDR • Measurement of stable isotope for comparison with other experimental data • Measurement of PDR in complete Sn isotopic chain below and above the neutron threshold • Measurement of (g,xn) and (g,g’) channels • PDR strength distribution independent of neutron threshold D. Rossi

  6. Coulomb Excitation at Relativistic Energies Heavy-ion-induced electromagnetic excitation, via the virtual photon approach Short lifetime of projectile  requires experiment in inverse kinematics Reconstruction of excitation energy (using invariant mass) of each event requires detection of ALL participating species (identification and momentum) Measurements on Pb, C and empty targets allows the separation of the electromagnetic, nuclear and background components b = 0.6 - 0.8 Sn Sn Sn E2 E1 M1 Pb n D. Rossi

  7. Aim of Proposed Experiment (cont’d) • Measurement of GQR in 124Sn to 128Sn • Two beam energies required to disentangle E1 and E2 components • Requires total E1+E2 strength distribution with good statistics 2*105events simulated E1 E2 • Example: • 132Sn at 600 and 300 AMeV • 100% TRK sum rule strength for E1 • 100% EWSR strength for E2 600 AMeV E1 E2 extracted E2 strength 300 AMeV D. Rossi

  8. Aim of Proposed Experiment (cont’d) • Investigation of the isospin character of the low-lying dipole strength • Nuclear inelastic scattering with an isoscalar probe, using (d,d’g) • Analysis of photon decay branch allows the selection of dipole excitations • Foreseen for high-statistics beams, such as 124Sn and 128Sn J. Endres et al., Phys. Rev. C 80, 034302 (2009) D. Rossi

  9. Experiment Overview Aims of proposed experiment: Systematic investigation of E1 strength in Sn isotopic chain from A = 124 to 134 PDR measurement below and above the neutron threshold Measurement of E2 strength in 124Sn to 128Sn Excitation with isoscalar probe (CD2 target) Improvements compared to previous experiments Better mass resolution Improved detector response Better statistics D. Rossi

  10. Fragment mass Reconstruction of fragment mass: measurement of flight trajectory, after deviation in magnetic field Current mass resolution: s = 0.5% Mass resolution aim for future experiment: s = 0.3 A for A = 132 New features: Vacuum pipe for fragments up to the last position measurement New plastic fiber detector for first position measurement after magnet; 250 mm pitch and 250 mm thickness D. Rossi

  11. Other Technical Improvements • New readout electronics for LAND and Crystal Ball • Incoming tracking with diamond or Si microstrip detector • Use of thinner Pb target (100 mg/cm2) for (g,g’) measurements  reduction of amount of Bremsstrahlung • Example: • Bremsstrahlung spectrum non-interacting Sn isotopes • 500 mg/cm2 Pb target • Measured with CB detector D. Rossi

  12. Summary of Beam-time Request D. Rossi

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