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Phys Rev Lett. 2018 Apr 13;120(15):152504. doi: 10.1103/PhysRevLett.120.152504.

Strong Neutron Pairing in core+4n Nuclei.

Author information

1
Grand Accélérateur National d'Ions Lourds (GANIL), CEA/DRF-CNRS/IN2P3, Bvd Henri Becquerel, 14076 Caen, France.
2
LPC Caen, ENSICAEN, Université de Caen, CNRS/IN2P3, F-14050 CAEN Cedex, France.
3
Institut für Kernphysik, Technische Universität Darmstadt, 64289 Darmstadt, Germany.
4
GSI Helmholtzzentrum für Schwerionenforschung, 64291 Darmstadt, Germany.
5
Irfu, CEA, Université Paris-Saclay, 91191 Gif-sur-Yvette, France.
6
IGFAE, Instituto Galego de Física de Altas Enerxías, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain.
7
Department of Physics, Lund University, 22100 Lund, Sweden.
8
National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.
9
Helmholtz-Zentrum Dresden-Rossendorf, 01328, Dresden, Germany.
10
Department of Physics and Astronomy, Texas A&M University-Commerce, Commerce, Texas 75429, USA.
11
Instituto de Estructura de la Materia, CSIC, Serrano 113 bis, 28006 Madrid, Spain.
12
University of Vigo, 36310 Vigo, Spain.
13
Department of Physics, University of Surrey, Guildford GU2 7XH, United Kingdom.
14
Oliver Lodge Laboratory, University of Liverpool, Liverpool L69 7ZE, United Kingdom.
15
NRC Kurchatov Institute, Ru-123182 Moscow, Russia.
16
ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291 Darmstadt, Germany.
17
Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal.
18
Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal.
19
Saha Institute of Nuclear Physics, 1/AF Bidhan Nagar, Kolkata 700064, India.
20
II. Physikalisches Institut, Universität Gieß en, 35392 Gießen, Germany.
21
MTA Atomki, 4001 Debrecen, Hungary.
22
School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom.
23
Grupo de Física Nuclear y UPARCOS, Universidad Complutense de Madrid, CEI Moncloa, 28040 Madrid, Spain.
24
School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, United Kingdom.
25
Laboratório de Instrumentação e Física Experimental de Partículas-LIP, 1000-149 Lisbon, Portugal.
26
Physik Department E12, Technische Universität München, 85748 Garching, Germany.
27
Goethe-Universität Frankfurt am Main, 60438 Frankfurt am Main, Germany.
28
Institutionen för Fysik, Chalmers Tekniska Högskola, 412 96 Göteborg, Sweden.
29
IPHC-CNRS/Université de Strasbourg, 67037 Strasbourg, France.
30
KVI-CART, University of Groningen, Zernikelaan 25, 9747 AA Groningen, The Netherlands.
31
Astronomy and Physics Department, Saint Mary's University, Halifax, Nova Scotia B3H 3C3, Canada.
32
STFC Daresbury Laboratory, WA4 4AD Warrington, United Kingdom.
33
Laboratório de Instrumentação, Engenharia Biomédica e Física da Radiação (LIBPhysUNL), Departamento de Física, Faculdade de Ciências e Tecnologias, Universidade Nova de Lisboa, 2829-516 Monte da Caparica, Portugal.
34
Department of Physics, University of York, Heslington, York YO10 5DD, United Kingdom.
35
Institut für Kern- und Teilchenphysik, Technische Universität Dresden, 01069 Dresden, Germany.
36
Department of Physics, Tokyo Institute of Technology, 2-12-1 O-Okayama, Meguro, Tokyo 152-8551, Japan.
37
Institut für Kernphysik, Universität zu Köln, 50937 Köln, Germany.

Abstract

The emission of neutron pairs from the neutron-rich N=12 isotones ^{18}C and ^{20}O has been studied by high-energy nucleon knockout from ^{19}N and ^{21}O secondary beams, populating unbound states of the two isotones up to 15 MeV above their two-neutron emission thresholds. The analysis of triple fragment-n-n correlations shows that the decay ^{19}N(-1p)^{18}C^{*}→^{16}C+n+n is clearly dominated by direct pair emission. The two-neutron correlation strength, the largest ever observed, suggests the predominance of a ^{14}C core surrounded by four valence neutrons arranged in strongly correlated pairs. On the other hand, a significant competition of a sequential branch is found in the decay ^{21}O(-1n)^{20}O^{*}→^{18}O+n+n, attributed to its formation through the knockout of a deeply bound neutron that breaks the ^{16}O core and reduces the number of pairs.

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