1. Nuclear excitations in nucleon removal processes
SPES 2014
Second International Workshop
Legnaro, Italy, May 26-28, 2014
Nuclear excitations in nucleon removal processes
José Benlliure
Universidad de Santiago de Compostela
Spain

2. Nucleon-removal processes
Interplay between fragmentation and nuclear structure
Production of neutron-rich nuclei
Structural properties
The puzzling quenching of deeply bound nucleons
Access to unbound systems
José Benlliure, SPES 2014
Legnaro, Italy,, May 2014 2

3. Experimental approach
Inverse kinematics
GSI
José Benlliure, SPES 2014
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4. Experimental approach
Inverse kinematics
GSI
More than 1000 fission
fragments identified in the reaction 238U(1 A GeV)+d
José Benlliure, SPES 2014
Legnaro, Italy, May 2014

5. Multinucleon-removal reactions
Isospin fluctuations
the abrasion process is isospin independent:
hot pre-fragments
prefragments with large N/Z fluctuations
most of the prefragments do not survive because
of the excitation energy gained
cold final-residues
- nature of final fragments governed by neutron-proton evaporation:
N/Z fluctuations are reduced
José Benlliure, SPES 2014
Legnaro, Italy, May 2014

6. Producing nuclei far from stability
Nuclei far from stability in nucleon-removal/fragmentation reactions
Fragmentation is an optimum reaction mechanism for exploring the nuclide chart:
neutron-deficient nuclei are highly populated
up to the drip-line
the in-flight fragmentation of heavy nuclei
leading to fission produces medium-mass
neutron-rich nuclei
the large fluctuation in isospin (abrasion) and
excitation energy (ablation) give access to
cold fragmentation processes where
neutron-rich nuclei are produced.
José Benlliure, SPES 2014
Legnaro, Italy, May 2014 6

7. Producing nuclei far from stability
Heavy neutron-rich nuclei
238U + 1 A GeV
208Pb + 1 A GeV
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8. Producing nuclei far from stability
Heavy neutron-rich nuclei
238U+Be 1000 A MeV
H. Alvarez et al., PRC 82, ( 2010)
208Pb+Be 1000 A MeV
T. Kurtukian et al., PRC 89, ( 2014)
J. Kurcewicz et al., PLB 717, 371 ( 2012)
238U+Be 1000 A MeV
H. Alvarez et al., PRC 82, ( 2010)
238U+Be 1000 A MeV
H. Alvarez et al., PRC 82, ( 2010)
208Pb+Be 1000 A MeV
T. Kurtukian et al., PRC 89, ( 2014)
126 new heavy neutron-rich nuclei
fragmenting beams of 238U and 208Pb
José Benlliure, SPES 2014
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9. Production of heavy neutron-rich nuclei
Predicted cross sections with ABRASION/ABLATION
models
The measured cross sections are only reproduced when
highly excited remnants are considered. On average the
remnant gains 27 MeV per abraded nucleon.
- EPAX
- COFRA
José Benlliure, SPES 2014
T. Kurtukian et al., PRC 89, (2014)
Legnaro, Italy, May 2014

10. The puzzling quenching of the spectroscopic factors
Knock-out versus transfer
A. Gade et al., PRC 77, (2008)
F. Flavigny et al., PRL 110, (2013)
“The disagreement of the two systematic trends from knockout and transfer calls for a better description of so-called direct reaction mechanisms in order that a consistent picture of nuclear structure emerges from measurements at different incident energies.”
José Benlliure, SPES 2014
Legnaro, Italy, May 2014

11. Nuclear excitations in proton knock-out
Model description: Glauber model
Adiabatic and inert-core approximations
core survival
probability
1-N removal
probability
Explicit treatment of core excitations was suggested for the 1-N quenching puzzle
A-1X core
A-2X core
A. Bonaccorso
C. Louchart et al., PRC 83, (2011)
evaporation
José Benlliure, SPES 2014
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12. Nuclear excitations in proton knock-out
Proton knock-out at FRS/GSI
José Benlliure, SPES 2014
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13. Nuclear excitations in proton knock-out
Measurements at FRS/GSI
José Benlliure, SPES 2014
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14. Nuclear excitations in proton knock-out
Model description: abrasion-ablation
The probability for nucleon removal processes is
defined by the geometrical overlap between
projectile and target nuclei
Remnants survive when excited below the neutron evaporation threshold (Sn).
Excitations of the residual nuclei are considered
from the holes created in the Fermi distribution
of single-particle levels.
José Benlliure, SPES 2014
Legnaro, Italy,, May 2014 14

15. Nuclear excitations in proton knock-out
Data interpretation
Excitation energy gained by the remnants seems to
be larger than expected from particle-hole excitations
K.-H. Schmidt et al., PLB 300, 313 (1993)
José Benlliure, SPES 2014
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16. Nuclear excitations in proton knock-out
Data interpretation
The persistence of this effect should be checked with
lighter projectiles and as a function of the neutron excess.
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17. Nucleon excitations in proton knock-out
Isospin dependence of the nucleon-removal process Sn
106
107
108
109
110 In
115
125
124
123
122
121
120
119
118
117
116
114
113
112
111 Sb Te
126 Sn
132
238U beam
D. Pérez et al., PLB 703 (2011) 552
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18. Nucleon excitations in proton knock-out
Isospin dependence of the proton-removal process
Calculations validated with stable beams underestimate the survival probability
of proton knock-out residues obtained with neutron-deficient beams.
José Benlliure, SPES 2014
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19. Nucleon excitations in proton knock-out
Isospin dependence of the nucleon-removal process
The excitation energy induced by nucleon removal seems to be enhanced for the deficient species in systems with large neutron-proton asymmetries.
José Benlliure, SPES 2014
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20. Nucleon excitations in proton knock-out
Isospin dependence of the nucleon-removal process
Protons and neutrons exchange their role in neutron-rich and proton-rich nuclei.
José Benlliure, SPES 2014
Legnaro, Italy, May 2014 20

21. Nucleon excitations in proton knock-out
Isospin dependence of the nucleon-removal process
Sn > Sp
Vn > Vp
Sn = Sp
Vn > Vp
Sn < Sp
Vn < Vp
José Benlliure, SPES 2014
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22. Nucleon excitations in proton knock-out
Isospin dependence of the nucleon-removal process
Sn > Sp
Vn > Vp
Sn = Sp
Vn > Vp
Sn < Sp
Vn < Vp
José Benlliure, SPES 2014
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23. Nucleon excitations in proton knock-out
Isospin dependence of the proton-removal process
Sn > Sp
Vn > Vp
Sn = Sp
Vn > Vp
Sn < Sp
Vn < Vp
José Benlliure, SPES 2014
Legnaro, Italy, May 2014 23

24. Conclusions
Multinucleon-removal reactions play a key role in the production of nuclei far from stability because of the large fluctuations in isospin and excitation energy gained in these processes.
According to abrasion-ablation model calculations, the production cross sections of nucleon knock-out process can only be described when remnant excitations are considered.
This isospin dependence of the excitation could be related to the quenching of the spectroscopic factors in nucleon knock-out. However, more realistic model calculations and transfer data in similar systems should be used for a final interpretation.
Collaborators:
U. Santiago de Compostela: J. Vargas, J.L. Rodríguez, Y. Ayyad, S. Beceiro, D. Cortina, P. Díaz,
M. Mostazo, C. Paradela
GSI: T. Aumann, J. Atkinson, K. Boretzky, A. Estrade, H. Geissel, A. Kelic, Y. Litvinov, S. Pietri,
A. Prochazka, M. Takechi, J. Winfield
CEA/DAM: A. Chatillon, J. Taieb
José Benlliure, SPES 2014
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