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The Giant Dipole Resonance, new measurements F. Camera

The Giant Dipole Resonance, new measurements F. Camera University of Milano and INFN sect. of Milano HECTOR Collaboration Giant Dipole Resonance in very Hot Nuclei Temperature dependence of the GDR width Dipole Response in neutron rich nuclei Pigmy Dipole Resonance in 68 Ni.

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The Giant Dipole Resonance, new measurements F. Camera

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  1. The Giant Dipole Resonance, • new measurements • F. Camera • University of Milano and INFN sect. of Milano • HECTOR Collaboration • Giant Dipole Resonance in very Hot Nuclei • Temperature dependence of the GDR width • Dipole Response in neutron rich nuclei • Pigmy Dipole Resonance in 68Ni

  2. v/c < 5 % Fusion-Evaporation reactions Pygmy Dipole Resonance in neutron rich g.s. nuclei GDR in HOT nuclei Relativistic Coulomb excitation (v/c ~ 0.8%) CN g-decay spectra + Statistical Model GDR (EWSR, EoG, lineshape) g Coulex Ground State g-decay spectra GDR/PDR (EWSR, EoG, lineshape)

  3. GDR width in hot 132Ce Nuclei A ~ 110 P. Chomaz et al. Nucl. Phys. A569(1994)203 E. Ormand et al. Phys. Rev. lett. 69(1992)2905 A. Smerzi et al. Phys. Lett. B320 (1994)16 T. Suomijarvi et al. Phys. Rev. C53(1996)2258 J.H. Le Faou et al. Phys. Rev. Lett. 72(1996)2258 A. Bracco et al. 62(1989)2080 D.R. Chakrabarty et al. Phys. Rev. C36(1987)1886 A. Bracco et al. Phys. Rev. Lett. 62(1989)2080 R. Vojetech et al. Phys. Rev. C 40(1989)R2441 G. Enders et al. Phys. Rev. Lett. 69(1992)249 H.J. Hoffman et al Nucl. Phys. A571(1994)301 • For E*/A < 1.2 (T < 2 MeV) the GDR width increases with excitation energy • Mostly Spin induced effect • As the beam energy increases • Compound nucleus E* increases • Compound nucleus average spin increases • The nucleus becomes more and more deformed • The GDR components splits • The GDR width increases • For E*/A > 1.2 (T > 2 MeV) the GDR width seams to saturate • Saturation of the angular momentum that compound nucleus may sustain • Compound decay width • TFM prediction • Alternative models to TFM predict that G0 increases

  4. A stronger than expected, non evaporative, emission forward focused was measured Pre-equilibrium particles and multiplicity indicate a reduction in the compound nucleus E* 18O + 100Mo = 118Sn High energy g-rays + Light Charged particles The data from other groups has been reanalyzed to account for pre-equilibrium All the ‘high temperature’ points has been corrected and shifted to lower energy The GDR width does not saturate anymore NEW Exclusive experiment 2 < T < 4 MeV High energy gamma rays Light charged particles Fusion residues No pre-equilibrium emission M.P. Kelly et al. Phys. Rev. C 56(1997)3201 M.P. Kelly et al. Phys. Rev. Lett. 82(1999)3404 M.P. Kelly et al. Phys. Rev. Lett. 82(1999)3404

  5. HECTOR + GARFIELD ( INFN Legnaro Laboratories) BaF2ÞHigh energy g-rays Garfield ÞCharged Particles PPAC ÞMass selection Two reactions – Same compound 16O (130,250 MeV ) + 116Sn Þ132Ce* 64Ni (300,400,500 MeV) + 68Zn Þ132Ce*

  6. ALPHA PARTICLE SPECTRA Alpha particle spectra Blue = experimental data Red = moving source fit (CN source) Same excitation energy from Kinematics but very different alpha particle spectra Nickel induced reactions have only a thermal emission while Oxygen induced reactions have a strong component of pre-equilibrium emission GDR data in Nickel induced reactions does not need any ‘correction’ for the compound nucleus temperature

  7. 64Ni (300, 400, 500 MeV) + 68Zn Þ132Ce*

  8. Ebeam = 400 MeV TCN = 3.2 MeV T=3.2 MeV T=1.6 T=0.7 MeV Nuclear Temperature High energy g-rays (GDR) are emitted in all the decay steps and does reflects GDR emission from hot CN only. The emission from the hot compound nucleus is the strongest but not the only present in the decay. At low temperature g spectrum reflects more the level density energy dependence then GDR line-shape Eg [MeV]

  9. GDR width in 132Ce hot Nuclei In mass region A ~ 130 the GDR width increases with temperature E.F.Garman et al. Phys.Rev. C 28(1983)2554 R.K.Voijtech et al. Phys.Rev C 40(1989)2441 O.Wieland et al Phys. Rev. Lett. 97, 012501 (2006) The thermal fluctuation model reproduce the experimental data if and only if the compound evaporation width is included in the calculations Within this scenario there is no space for a significant increase of the intrinsic width Go, namely of the collisional damping

  10. Giant Dipole Resonance Collective oscillation of neutrons against protons N Average Transition charge densities P Average Transition charge densities N Pygmy Resonance Collective oscillation of neutron skin against the core Richter NPA 731(2004)59

  11. Physics Case: Relativistic Coulex of 68Ni How collective properties changes moving to neutron rich nuclei Dipole strength shifts at low energy Collective or non-collective nature of the transitions? Stable nuclei  photoabsorption Exotic nuclei Virtual photon breakup LAND experiment Virtual photon scattering RISING experiment 48Ca 40Ca T. Hartmann PRL85(2000)274 Adrich et al. PRL 95(2005)132501

  12. Virtual photon scattering technique first experiment with a relativistic beam GDR - PYGMY Excitation • 400 MeV/u 68Ni (2004) + 197Au • 600 MeV/u 68Ni (2005) + 197Au T.Aumann et al EPJ 26(2005)441 GDR - PYGMY Decay Coulex g

  13. RISING ARRAY Euroball 15 Clusters Located at 16.5°, 33°, 36° degrees Energetic threshold ~ 100 keV Hector BaF2 Located at 142° and 90° degrees Energetic threshold ~ 1.5 MeV Miniball segmented detectors Located at 46°, 60°, 80°, 90°degrees Energetic threshold ~ 100 keV Beam identification and tracking detectors Before and after the target Calorimeter Telescope for beam identification (CATE) 4 CsI 9 Si

  14. Incoming 68Ni beam 68Ni AoQ Z Coulomb excitation of 68Ni (600 MeV A) Outgoing 68Ni E (CsI) 1.2 % 4.4 % DE (Si) ~ 6 Days of effective beam time ~ 400 GB of data recorded ~ 3 107 ‘ good 68Ni events ‘ recorded

  15. Coulomb excitation of 68Ni (600 MeV A) Pygmy Dipole Resonance Preliminary Preliminary Preliminary GEANT Simulations A structure appears at 10-11 MeV in all detector types

  16. Coulomb excitation of 68Ni (600 MeV A) Pygmy Dipole Resonance BaF2 at 90° BaF2 at 142° Preliminary Preliminary Eg[MeV] The structure does not appears at 142° because of the much higher background

  17. Coulomb excitation of 67Ni (600 MeV A) The peak structure is roughly 2 MeV lower than in 68NI There is indication from a more fragmented structure In all cases the measured width is consistent with that extracted from GEANT simulations with a monochromatic g source Resonance width G < 1 MeV Preliminary

  18. RPA RMF Preliminary 68Ni 68Ni ~10 MeV ~10 MeV G. Colo private communications D. Vretnar et al. NPA 692(2001)496 Both RPA and RMF approaches predict for 68Ni Pygmy strength at approximately 10 MeV for 68Ni. The degree of collectivity is still debated Prediction are available only for 68Ni In the case of 67Ni as it is a vibration of the neutron skin it is important the value of the neutron binding energy. As a simple rule the localization in energy of the strength should be linearly correlated to the neutron binding energy Eb (68Ni)  7.8 MeV Eb (67Ni)  5.8 MeV

  19. Coulomb excitation of 68Ni (600 MeV A) The extraction of the B(E1) strength requires the estimation of the direct and compound g-decay of the dipole state to the ground state The compound term depends on the ratio between the gamma and total decay width J.Beene et al PRC 41(1990)920 The gamma decay width depends on The value of the level density at the resonance energy J.Beene et al PLB 164(1985)19 S.I.Al-Quiraishi PRC 63(2001)065803

  20. Conclusions • The GDR width has been measured in 132Ce up to T=4 MeV, a linear increase with temperature has been observed. • Pre-equilibrium emission strongly depends from the reaction channel. With symmetric reactions and simultaneous measurements of • particles and gamma-rays it was possible to establish the • excitation energy of the CN. • Data are well reproduced by the thermal fluctuations model if and only if the compound nucleus width is taken into account in the calculations. • We have measured high energy g-rays from Coulex of 68Ni at 600 MeV/u. • Strength at 10.5 MeV has been observed in all three kind of detectors • Peaks line-shape is consistent with GEANT simulations (GPDR < 1 MeV) • Low Energy Dipole strength has also been observed in 67Ni and 69Ni • Spectra and Numbers are preliminary

  21. HECTOR – GARFIELD Collaboration F.C. , A. Bracco, S. Brambilla, G.Benzoni, M.Casanova, F.Crespi, S. Leoni, A.Giussani, P.Mason, B.Million, D.Montanari, A.Moroni, O.Wieland, N.Blasi Dipartimento di Fisica, Universitá di Milano and I.N.F.N. Section of Milano, Milano Italy A.Maj, M.Kmiecik, M.Brekiesz, W.Meczynski, J.Styczen, M.Zieblinski, K.Zuber Niewodniczanski Institute of Nuclear Physics Krackow Poland F.Gramegna,S. Barlini, A. Lanchais, P.F. Mastinu L. Vannucci, V.L.Kravchuk INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy M. Bruno, M. D'Agostino, E. Geraci, G. Vannini INFN and Dipartimento di Fisica dell’Universita' di Bologna,, Bologna, Italy G. Casini, M. Chiari, A. Nannini INFN, Sezione di Firenze, Firenze, Italy U. Abbondanno, G.V. Margagliotti, P.M. Milazzo INFN and Dipartimento di Fisica Universita' di Trieste, Trieste, Italy A.Ordine INFN sez di Napoli, Napoli

  22. RISING Collaboration A.Bracco, G. Benzoni, N. Blasi, S.Brambilla, F. Camera, F.Crespi, S. Leoni, B. Million, M. Pignanelli, O. Wieland, University of Milano, and INFN section of Milano, Italy A.Maj, P.Bednarczyk, J.Greboz, M. Kmiecik, W. Meczynski, J. Styczen Niewodnicaznski institute of Nuclear Physics, Kracow, Poland T. Aumann, A.Banu, T.Beck, F.Becker, A.Burger, L.Cacieras, P.Doornenbal, H. Emling, J. Gerl, M.Gorska, J.Grebozs, O.Kavatsyuk, M.Kavatsyuk, I. Kojouharov, N. Kurtz, R.Lozeva, N.Saito, T.Saito, H.Shaffner, H. Wollersheim and FRS collaboration GSI J.Jolie, P. Reiter, N.Ward University of Koeln, Germany G. de Angelis, A. Gadea, D. Napoli, National Laboratory of Legnaro, INFN, Italy S. Lenzi, F. Della Vedova, E. Farnea, S. Lunardi, University of Padova and INFN section of Padova, Italy D.Balabanski, G. Lo Bianco, C. Petrache, A.Saltarelli, University of Camerino, Italy M. Castoldi and A. Zucchiatti, University of Genova, Italy G. La Rana, University of Napoli, Italy J.Walker, University of Surrey

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