title: Measurement of the isoscalar monopole response in the neutron-rich nucleus 68Ni.
abstract: The isoscalar monopole response has been measured in the unstable nucleus (68)Ni using inelastic alpha scattering at 50A  MeV in inverse kinematics with the active target MAYA at GANIL. The isoscalar giant monopole resonance (ISGMR) centroid was determined to be 21.1 ± 1.9 MeV and indications for a soft monopole mode are provided for the first time at 12.9 ± 1.0 MeV. Analysis of the corresponding angular distributions using distorted-wave-born approximation with random-phase approximation transition densities indicates that the L = 0 multipolarity dominates the cross section for the ISGMR and significantly contributes to the low-energy mode. The L=0 part of this low-energy mode, the soft monopole mode, is dominated by neutron excitations. This demonstrates the relevance of inelastic alpha scattering in inverse kinematics in order to probe both the ISGMR and isoscalar soft modes in neutron-rich nuclei.
authors.affiliation: IPN Orsay, Université Paris Sud, IN2P3-CNRS, F-91406 Orsay Cedex, France and LPC Caen, ENSICAEN, Université de Caen, CNRS/IN2P3, F-14050 CAEN Cedex, France.
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authors.affiliation: LPC Caen, ENSICAEN, Université de Caen, CNRS/IN2P3, F-14050 CAEN Cedex, France.
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authors.affiliation: IPN Orsay, Université Paris Sud, IN2P3-CNRS, F-91406 Orsay Cedex, France.
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authors.affiliation: LPC Caen, ENSICAEN, Université de Caen, CNRS/IN2P3, F-14050 CAEN Cedex, France.
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authors.affiliation: RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
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authors.affiliation: IPN Orsay, Université Paris Sud, IN2P3-CNRS, F-91406 Orsay Cedex, France.
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authors.affiliation: IPN Orsay, Université Paris Sud, IN2P3-CNRS, F-91406 Orsay Cedex, France.
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authors.lastname: Blumenfeld
authors.affiliation: Universidade de Santiago de Compostela, E-15706 Santiago de Compostela, Spain.
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authors.lastname: Caamaño
authors.affiliation: Grand Accélérateur National d'Ions Lourds (GANIL), CEA/DSM-CNRS/IN2P3, Bvd Henri Becquerel, 14076 Caen, France.
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authors.affiliation: Dipartimento de Fisica Università degli Studi di Milano and INFN, Sezione di Milano, 20133 Milano, Italy.
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authors.affiliation: LPC Caen, ENSICAEN, Université de Caen, CNRS/IN2P3, F-14050 CAEN Cedex, France.
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authors.lastname: Delaunay
authors.affiliation: Universidade de Santiago de Compostela, E-15706 Santiago de Compostela, Spain.
authors.forename: B
authors.initials: B
authors.lastname: Fernandez-Dominguez
authors.affiliation: Physics Department, University of Notre Dame, Notre Dame, Indiana 46556, USA.
authors.forename: U
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authors.affiliation: Grand Accélérateur National d'Ions Lourds (GANIL), CEA/DSM-CNRS/IN2P3, Bvd Henri Becquerel, 14076 Caen, France.
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authors.initials: GF
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authors.affiliation: Grand Accélérateur National d'Ions Lourds (GANIL), CEA/DSM-CNRS/IN2P3, Bvd Henri Becquerel, 14076 Caen, France and KVI-CART, University of Groningen, NL-9747 AA Groningen, The Netherlands.
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authors.lastname: Harakeh
authors.affiliation: KVI-CART, University of Groningen, NL-9747 AA Groningen, The Netherlands.
authors.forename: N
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authors.lastname: Kalantar-Nayestanaki
authors.affiliation: National Centre for Nuclear Research ul. Andrzeja Soł tana 7, 05-400 Otwock, Poland.
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authors.lastname: Keeley
authors.affiliation: NSCL, Michigan State University, East Lansing, Michigan 48824-1321, USA.
authors.forename: W
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authors.lastname: Mittig
authors.affiliation: Grand Accélérateur National d'Ions Lourds (GANIL), CEA/DSM-CNRS/IN2P3, Bvd Henri Becquerel, 14076 Caen, France.
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authors.lastname: Pancin
authors.affiliation: Instituut voor Kern- en Stralingsfysica, KU Leuven, B-3001 Leuven, Belgium.
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authors.lastname: Raabe
authors.affiliation: Grand Accélérateur National d'Ions Lourds (GANIL), CEA/DSM-CNRS/IN2P3, Bvd Henri Becquerel, 14076 Caen, France and Instituut voor Kern- en Stralingsfysica, KU Leuven, B-3001 Leuven, Belgium.
authors.forename: T
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authors.affiliation: Grand Accélérateur National d'Ions Lourds (GANIL), CEA/DSM-CNRS/IN2P3, Bvd Henri Becquerel, 14076 Caen, France.
authors.forename: H
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authors.lastname: Savajols
authors.affiliation: Grand Accélérateur National d'Ions Lourds (GANIL), CEA/DSM-CNRS/IN2P3, Bvd Henri Becquerel, 14076 Caen, France.
authors.forename: O
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authors.affiliation: Grand Accélérateur National d'Ions Lourds (GANIL), CEA/DSM-CNRS/IN2P3, Bvd Henri Becquerel, 14076 Caen, France.
authors.forename: C
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authors.lastname: Stodel
authors.affiliation: IPN Orsay, Université Paris Sud, IN2P3-CNRS, F-91406 Orsay Cedex, France and NSCL, Michigan State University, East Lansing, Michigan 48824-1321, USA.
authors.forename: D
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authors.affiliation: Grand Accélérateur National d'Ions Lourds (GANIL), CEA/DSM-CNRS/IN2P3, Bvd Henri Becquerel, 14076 Caen, France.
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