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Pair and Single Neutron Transfer with Borromean 8He A View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by HAL-CEA Pair and single neutron transfer with Borromean 8He A. Lemasson, A. Navin, M. Rejmund, N. Keeley, V. Zelevinsky, S. Bhattacharyya, A. Shrivastava, Dominique Bazin, D. Beaumel, Y. Blumenfeld, et al. To cite this version: A. Lemasson, A. Navin, M. Rejmund, N. Keeley, V. Zelevinsky, et al.. Pair and single neutron transfer with Borromean 8He. Physics Letters B, Elsevier, 2011, 697, pp.454-458. <10.1016/j.physletb.2011.02.038>. <in2p3-00565792> HAL Id: in2p3-00565792 http://hal.in2p3.fr/in2p3-00565792 Submitted on 14 Feb 2011 HAL is a multi-disciplinary open access L'archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destin´eeau d´ep^otet `ala diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publi´esou non, lished or not. The documents may come from ´emanant des ´etablissements d'enseignement et de teaching and research institutions in France or recherche fran¸caisou ´etrangers,des laboratoires abroad, or from public or private research centers. publics ou priv´es. Pair and single neutron transfer with Borromean 8He A. Lemassona,1, A. Navina,∗, M. Rejmunda, N. Keeleyb, V. Zelevinskyc, S. Bhattacharyyaa,d, A. Shrivastavaa,e, D. Bazinc, D. Beaumelf, Y. Blumenfeldf, A. Chatterjeee, D. Guptaf,2, G. de Francea, B. Jacquota, M. Labicheg, R. Lemmong, V. Nanalh, J. Nybergi, R. G. Pillayh, R. Raabea,3, K. Ramachandrane, J.A. Scarpacif, C. Schmitta, C. Simenelj, I. Stefana,f,4, C.N. Timisk aGANIL, CEA/DSM - CNRS/IN2P3, Bd Henri Becquerel, BP 55027, F-14076 Caen Cedex 5, France bDepartment of Nuclear Reactions, The Andrzej Soltan Institute for Nuclear Studies, ul. Ho˙za 69, PL-00-681 Warsaw, Poland cNSCL and Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA dVariable Energy Cyclotron Centre, 1/AF Bidhan Nagar, Kolkata 700064, India eNuclear Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India fInstitut de Physique Nucl´eaire,IN2P3-CNRS, 91406 Orsay, France gCRLC, Daresbury Laboratory, Daresbury, Warrington, WA4 4AD, U.K. hDepartment of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Mumbai 400005, India iDepartment of Physics and Astronomy, Uppsala University, Uppsala, Sweden jIRFU/Service de Physique Nucl´eaire, CEA Centre de Saclay, F-91191 Gif-sur-Yvette, France kDepartment of Physics, University of Surrey, Guildford, GU2 7XH, U.K. Abstract Direct observation of the survival of 199Au residues after 2n transfer in the 8He+197Au system and the absence of the corresponding 67Cu in the 8He+65Cu system at various energies are reported. The measurements of the surprisingly large cross sections for 199Au, coupled with the integral cross sections for the various Au residues, is used to obtain the first model-independent lower limits on the ratio of 2n to 1n transfer cross sections from 8He to a heavy target. A comparison of the transfer cross sections for 6,8He on these targets highlights the differences in the interactions of these Borromean nuclei. These measurements for the most neutron-rich nuclei on different targets highlight the need to probe the reaction mechanism with various targets and represent an experimental advance towards understanding specific features of pairing in the dynamics of dilute nuclear systems. Keywords: Borromean nucleus, Transfer reaction, Excitation function The recent developments in a variety of fields like nuclei pairing correlations and therefore can be characterized as far from stability, cold atoms in traps, nanoscale condensed a pure embodiment of the Cooper effect [3] with one or matter devices or quantum computing systems show how two pairs in restricted geometry. Such structures in small quantum-statistical and dynamic correlations between the composite objects are known to influence quantum tunnel- constituents build the structure of the system. Neutron- ing [4]. rich radioactive nuclei, with their extended and therefore Pairing correlations in small fermionic systems [5], re- dilute matter distributions and extreme sensitivity to the sponsible for extra binding, odd-even staggering, and mod- precise particle number, provide unique opportunities to ification of single-particle and collective properties, have study the complexity and structurization of an aggregate common features with macroscopic superconductors but of quantum particles [1, 2]. Light neutron-rich nuclei also at the same time reveal some differences due to their meso- carry indispensable information on properties of neutron scopic nature. In nuclei the formally calculated coher- matter. Borromean nuclei (bound three-body systems ence length of a Cooper pair is larger than the size of 6,8 with unbound two-body subsystems), such as He and the nucleus, the energy gap appears on the background of 11 Li, provide an example of binding arising essentially from a distinct shell structure, while all phase transitions are smeared. As the role of pairing correlations in nuclear ∗Corresponding author structure is well known, it is of great interest to get exper- Email address: [email protected] (A. Navin) imental information on their dynamical aspects, especially 1Present address: National Superconducting Cyclotron Labora- tory, Michigan State University, East Lansing, MI 48824, USA involving Borromean nuclei. Nucleon transfer reactions, 2Permanent address: Dept. of Physics and Centre for Astroparti- particularly on heavy targets, are an important tool for cle Physics and Space Science, Bose Institute, Kolkata 700091, India. 3 such studies [6]. The energy dependence of tunneling, re- Permanent address: Instituut voor Kern- en Stralingsfysica, lated to the two-particle strength functions, probes the K.U. Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium. 4Permanent address: Institut de Physique Nucleaire, IN2P3- interaction responsible for pair formation in nuclei. The CNRS, 91406 Orsay, France. signatures of related phenomena like the nuclear (ac and Preprint submitted to Physics Letters B February 14, 2011 8 197 8He+65Cu He+ Au 10 (a) ▲ Triple coincidence 12 6 (b) (a) 15 (b) 198m He 100 6He−n 8 Au 8 8 80 4 214.5 4 500 199 He Counts / h He 50 ▲ Au 0 ▲ ▲ ▲ 0 50 100 Counts/keV ▲ 6 Time (h) 10 α 0 201 150 300 450 * Tl 204.1 333.8 * E (MeV) Eγ (keV) Au K ∆ 4 40 300 180.3 dE (mb/sr/MeV) Counts/keV Ω E* 5 /d 2 Counts / 0.5 keV σ d Sn Qgg 0 0 100 0 5 10 15 20 25 −10 0 10 20 150 170 190 100 200 300 E (MeV) lab Q (MeV) Eγ (keV) Eγ (keV) Figure 1: (color online) (a) ∆E − E matrix for 8He + 65Cu at Figure 2: (color online) (a) A portion of the off-beam γ-ray spectrum ◦ 6 8 197 Elab = 19.9 MeV, θlab = 35.6 . (b) Q-value spectrum for He at Elab = 22.9 MeV for the He+ Au system showing the 158.4 detected in coincidence with the 186 keV γ transition in 66Cu. The keV γ ray emitted in the decay of 199Au. The corresponding back- ground state Q-value (Qgg) for 2n-stripping is shown. The Q-value ground spectrum is shown by the dotted line and known transitions spectrum was constructed assuming a binary reaction. The inset are denoted by asterisks. 201Tl is produced from a fusion-evaporation shows a triple coincidence spectrum of γ rays requiring the detection process. The inset shows the measured activity for 199Au fitted us- of 6He particles and neutrons (see text). Transitions in 66Cu are ing the known half-life. (b) γ-ray spectrum obtained in coincidence labeled (filled triangles). with the 97 keV transition from the decay of the 12− isomeric state (811.7 keV) in 198Au. dc) Josephson effect [7] have been discussed in recent re- than differential cross sections. views [6, 8]. Significant experimental advances [4, 9, 10, 11] Measurements were performed with 8He beams, pro- in reactions using low-intensity re-accelerated radioactive duced at the SPIRAL facility at GANIL, with typical in- ion beams (RIBs) of nuclei near the drip line, in particular tensities of (2 − 4) × 105 pps on 65Cu and 197Au targets, for Borromean nuclei around the Coulomb barrier, have re- employing two independent setups using in-beam and off- newed hopes for observing the transfer of a single Cooper beam techniques, respectively [21]. Neutron transfer reac- pair, “enhanced” pair transfer, and “giant pairing vibra- tions on 65Cu were investigated at 19.9 and 30.6 MeV using tions”. Measurements of the ratio of 2n- to 1n-transfer in-beam measurements of inclusive and exclusive angular cross sections (σ2n/σ1n) with Borromean nuclei are ex- distributions of light charged particles, γ rays and neu- pected to be sensitive to correlations among the valence 8 trons. The experimental setup consisted of 11 Compton neutrons [12, 13]. The He nucleus with four loosely bound suppressed clover HpGe detectors of the EXOGAM ar- valence neutrons provides a unique system for investigat- ray and an annular Si telescope covering an angular range ing the role of neutron correlations, including pairing, in of 25◦-60◦. Fig. 1(a) shows a ∆E − E identification plot. structure and dynamics of dilute nuclear systems. Addi- The observed α particles arise mainly from other processes, tionally the work done by the Dubna group [14, 15] allow e.g. decay of the compound nucleus. Neutrons were de- an interesting comparison to be made with the Borromean tected in a neutron wall consisting of 45 hexagonal detec- 6He to further highlight the role of the excess neutrons in 8 tors placed at 55 cm from the target. Further details are the doubly Borromean system He. given in Refs. [10, 22]. Coincidences between 6He and γ As opposed to transfer reactions with light ions (like rays from the transfer residue 66Cu were used to obtain (p,t) or (p,d) reactions) [16], studies involving heavy ions the Q-distribution shown in Fig.
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