The Giant Dipole Resonance, new measurements

F. CameraUniversity 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

GDR in HOT nuclei

from 16O induced reaction will be discussed in a following paper [ref]

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Pygmy Dipole Resonance in neutron rich g.s. nuclei

v/c < 5 %

Fusion-Evaporation reactions

from 16O induced reaction will be discussed in a following paper [ref]

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CN -decay spectra +Statistical Model

GDR (EWSR, Eo , lineshape)

Relativistic Coulomb excitation (v/c ~ 0.8%)

Coulex

Ground State -decay spectra

GDR/PDR (EWSR, Eo , lineshape)

D.R. Chakrabarty et al. Phys. Rev. C36(1987)1886A. 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 132Ce 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)203E. Ormand et al. Phys. Rev. lett. 69(1992)2905A. Smerzi et al. Phys. Lett. B320 (1994)16T. Suomijarvi et al. Phys. Rev. C53(1996)2258J.H. Le Faou et al. Phys. Rev. Lett. 72(1996)2258A. 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

18O + 100Mo = 118Sn

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

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MSU Data Th. Fluc. +

CN

Th. Fluc Seattle GSI Grenoble

FWHM

(MeV

)

T (MeV)

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 raysLight charged particles

Fusion residues

No pre-equilibrium emission

HECTOR + GARFIELD HECTOR + GARFIELD ( INFN Legnaro Laboratories)( INFN Legnaro Laboratories)

BaF2 High energy -raysGarfield Charged ParticlesPPAC Mass selection

Two reactions – Same compound

16O (130,250 MeV ) + 116Sn 132Ce*64Ni (300,400,500 MeV) + 68Zn 132Ce*

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

from 16O induced reaction will be discussed in a following paper [ref]

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

Nuclear Temperature

1E-10

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Ebeam = 400 MeVTCN = 3.2 MeV

T=3.2 MeV

T=1.6

T=0.7 MeV

High energy -rays (GDR) are emitted inall 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)

<T>

(MeV)

300 2.2 1.9 1.8

400 3.2 2.8 2.2

500 4.1 3.7 2.9

E.F.Garman et al. Phys.Rev. C 28(1983)2554R.K.Voijtech et al. Phys.Rev C 40(1989)2441O.Wieland et al Phys. Rev. Lett. 97, 012501 (2006)

GDR width in 132Ce 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

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Richter NPA 731(2004)59

Pygmy ResonanceCollective oscillation of neutron skin against the core

Giant Dipole ResonanceCollective 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 68Ni

How collective properties changes moving to neutron rich nuclei

T. Hartmann PRL85(2000)274

40Ca48Ca

Adrich et al. PRL 95(2005)132501

• 400 MeV/u 68Ni (2004) + 197Au

• 600 MeV/u 68Ni (2005) + 197Au

)2()( GDR

PbO 20816

T.Aumann et al EPJ 26(2005)441

GDR - PYGMY Decay

GDR - PYGMY Excitation

Virtual photon scattering techniquefirst experiment with a relativistic beam

Coulex

Euroball 15 Clusters

Located at 16.5°, 33°, 36° degreesEnergetic threshold ~ 100 keV

Hector BaF2

Located at 142° and 90° degreesEnergetic 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 CsI9 Si

Coulomb excitation of 68Ni (600 MeV A)

68Ni

Z

Ao

Q

Incoming 68Ni beam Outgoing 68Ni

E (Si)

E (

CsI

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1.2 %

4.4 %

0.00%

5.00%

10.00%

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25.00%

30.00%

35.00%

40.00%

66Co 67Ni 68Ni 69Ni 70Cu

~ 6 Days of effective beam time~ 400 GB of data recorded

~ 3 107 ‘ good 68Ni events ‘ recorded

Coulomb excitation of 68Ni (600 MeV A)

Pygmy Dipole Resonance

A structure appears at 10-11 MeV in all detector types

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68Ni

HPGe-Cluster

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68Ni

Baf2 Hector

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68NiHPGe MiniBall

Preliminary

Preliminary

Preliminary

Preliminary

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Preliminary

GEANT Simulations

Coulomb excitation of 68Ni (600 MeV A)

Pygmy Dipole Resonance

The structure does not appears at 142° because of the much higher background

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Baf2 Hector

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Preliminary

Preliminary

Preliminary

Preliminary

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Energy [MeV]

67Ni

HPGe Cluster

Coulomb excitation of 67Ni (600 MeV A)Pr

elim

inar

yThe 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 source

Resonance width < 1 MeV

Both RPA and RMF approaches predict for 68Ni Pygmy strength at approximately 10 MeV for 68Ni. The degree of collectivity is still debated

D. Vretnar et al. NPA 692(2001)496

RMF

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Energy (MeV)

mb

RPA

G. Colo private communications

68Ni 68Ni

Eb (68Ni) 7.8 MeV Eb (67Ni) 5.8 MeV

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

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~10 MeV~10 MeVPr

eliminary

Preliminary

Coulomb excitation of 68Ni (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

CN

CN

decay CEP00)1(

J.Beene et al PRC 41(1990)920

12 0

0

CN

J.Beene et al PLB 164(1985)19S.I.Al-Quiraishi PRC 63(2001)065803

The compound term depends on theratio 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 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 -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 (PDR < 1 MeV)

Low Energy Dipole strength has also been observed in 67Ni and 69Ni

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.ZuberNiewodniczanski Institute of Nuclear Physics Krackow Poland

F.Gramegna, S. Barlini, A. Lanchais, P.F. Mastinu L. Vannucci, V.L.KravchukINFN, Laboratori Nazionali di Legnaro, Legnaro, Italy

M. Bruno, M. D'Agostino, E. Geraci, G. VanniniINFN and Dipartimento di Fisica dell’Universita' di Bologna,, Bologna, Italy

G. Casini, M. Chiari, A. NanniniINFN, Sezione di Firenze, Firenze, Italy

U. Abbondanno, G.V. Margagliotti, P.M. MilazzoINFN and Dipartimento di Fisica Universita' di Trieste, Trieste, Italy

A.OrdineINFN 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. StyczenNiewodnicaznski 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 collaborationGSI

J.Jolie, P. Reiter, N.WardUniversity 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