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

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

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 GDR width in hot 132 Ce Nuclei 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  0 increases 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 A ~ 110

M.P. Kelly et al. Phys. Rev. C 56(1997)3201 High energy  -rays + Light Charged particles 18 O Mo = 118 Sn A stronger than expected, non evaporative, emission forward focused was measured M.P. Kelly et al. Phys. Rev. Lett. 82(1999)3404 Pre-equilibrium particles and multiplicity indicate a reduction in the compound nucleus E* 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 M.P. Kelly et al. Phys. Rev. Lett. 82(1999)3404 NEW Exclusive experiment 2 < T < 4 MeV High energy gamma rays Light charged particles Fusion residues No pre-equilibrium emission

HECTOR + GARFIELD ( INFN Legnaro Laboratories) BaF 2  High energy  -rays Garfield  Charged Particles PPAC  Mass selection Two reactions – Same compound 16 O (130,250 MeV ) Sn  132 Ce* 64 Ni (300,400,500 MeV) + 68 Zn  132 Ce*

Alpha particle spectra Blue = experimental data Red = moving source fit (CN source) ALPHA PARTICLE SPECTRA 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

64 Ni (300, 400, 500 MeV) + 68 Zn  132 Ce*

Nuclear Temperature E beam = 400 MeV T CN = 3.2 MeV T=3.2 MeV T=1.6 T=0.7 MeV High energy  -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  spectrum reflects more the level density energy dependence then GDR line-shape E  [MeV] Beam (MeV) T CN (MeV) T* (MeV) (MeV)

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, (2006) GDR width in 132 Ce hot Nuclei In mass region A ~ 130 the GDR width increases with temperature 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  o, namely of the collisional damping

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

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 Physics Case: Relativistic Coulex of 68 Ni How collective properties changes moving to neutron rich nuclei T. Hartmann PRL85(2000) Ca 48 Ca Adrich et al. PRL 95(2005)132501

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

Euroball 15 Clusters Located at 16.5°, 33°, 36° degrees Energetic threshold ~ 100 keV Hector BaF 2 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) RISING ARRAY 4 CsI 9 Si

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

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

Coulomb excitation of 68 Ni (600 MeV A) Pygmy Dipole Resonance The structure does not appears at 142° because of the much higher background E  [MeV] BaF 2 at 142°BaF 2 at 90° Preliminary Preliminary

Coulomb excitation of 67 Ni (600 MeV A) Preliminary The peak structure is roughly 2 MeV lower than in 68 NI 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  source Resonance width  < 1 MeV

Both RPA and RMF approaches predict for 68 Ni Pygmy strength at approximately 10 MeV for 68 Ni. The degree of collectivity is still debated D. Vretnar et al. NPA 692(2001)496 RMF RPA G. Colo private communications 68 Ni E b ( 68 Ni)  7.8 MeVE b ( 67 Ni)  5.8 MeV Prediction are available only for 68 Ni In the case of 67 Ni 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 ~ 10 MeV ~ 10 MeV Preliminary

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

Conclusions  The GDR width has been measured in 132 Ce 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  -rays from Coulex of 68 Ni 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 (  PDR < 1 MeV)  Low Energy Dipole strength has also been observed in 67 Ni and 69 Ni  Spectra and Numbers are preliminary

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 HECTOR – GARFIELD 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 RISING Collaboration