The exotic nucleus 8He is investigated by means of the measurement of the
angular distributions of the elastic channel and the 6He and 4He fragment yields produced
in the collision with a 208Pb target at two energies around the Coulomb barrier, 16 and
22 MeV. The experiment was performed at the GANIL-SPIRAL facility, with the aim of
extracting information about the structure of 8He and the relevant reaction mechanisms.
In this contribution, details of the experimental setup and preliminary data on elastic cross
sections are reported

Acosta Sánchez, Luis Armando

Berjillos Morente, Rafael

Borge, M. J. G.

Chbihi, A.

Cruz, C.

Cubero, M.

Dueñas Díaz, José Antonio

Fernández García, J. P.

Fernández Martínez, B.

Flores Garrido, Juan Luis

Gómez Camacho, Joaquín

Keeley, N.

Labrador, J. A.

Marqués, M.

Marquínez Durán, Gloria

Martel Bravo, Ismael

Mazzocco, M.

Moro, A. M.

Pakou, A.

Parkar, Vivek

Patronis, N.

Pesudo, V.

Pierrotsakou, D.

Raabe, R.

Rusek, K.

Silvestri, R.

Soić, N.

Standyło, Ł.

Strojek, I.

Sánchez Benítez, Ángel Miguel

Tengblad, Olof

Wolski, R.

Ziad, A. H.

Álvarez, M. A. G.

EPJ Web of Conferences

The exotic nucleus 8He is investigated by means of the measurement of the
angular distributions of the elastic channel and the 6He and 4He fragment yields produced
in the collision with a 208Pb target at two energies around the Coulomb barrier, 16 and
22 MeV. The experiment was performed at the GANIL-SPIRAL facility, with the aim of
extracting information about the structure of 8He and the relevant reaction mechanisms.
In this contribution, details of the experimental setup and preliminary data on elastic cross
sections are reported.Ciencias IntegradasIngeniería Eléctrica y Térmica, de Diseño y Proyecto

Arias Montano: Institutional Repository of the University of Huelva

Near barrier scattering of 8He on 208PbG. Marquínez-Durán1;a, A.M. Sánchez-Benítez2, I. Martel1, L. Acosta1;3, K. Rusek4, M.A.G Álvarez5;6, R. Berjillos1, M.J.G. Borge7, A. Chbihi8, C. Cruz7, M. Cubero7;9, J.A. Dueñas1, J.P. Fernández-García5;6, B. Fernández-Martínez5, J.L. Flores10, J. Gómez-Camacho5;6, N. Keeley11, J.A. Labrador5, M. Marqués12, A.M. Moro6, M. Mazzocco13, A. Pakou14, V.V. Parkar15, N. Patronis14, V. Pesudo7, D. Pierrotsakou16, R. Raabe17, R. Silvestri16, N. Soic18, Ł. Standylo11, I. Strojek11, O. Tengblad7, R. Wolski19;20, and A.H. Ziad51Departamento de Física Aplicada, Universidad de Huelva, 21071 Huelva, Spain2GSI Helmholtzzentrum für Schwerionenforschung Gmb, Planckstr. 1, 64291 Darmstadt, Germany3INFN Sezione di Catania. Via Santa Sofia 64 I-95123 Catania, Italy4Heavy Ion Laboratory, University of Warsaw, 02-093 Warsaw, Poland5Centro Nacional de Aceleradores, 41092, Sevilla6Departamento de Física Atómica, Molecular y Nuclear, Universidad de Sevilla, 41080 Sevilla, Spain7Instituto de Estructura de la Materia, CSIC, 28006 Madrid, Spain8GANIL, CEA and IN2P3-CNRS, B.P. 5027, 14076 Caen cedex, France9CICANUM, Universidad de Costa Rica UCR, Apartado 2060 San José, Costa Rica10Departamento de Ingeniería Eléctrica, Universidad de Huelva, 21071 Huelva, Spain11National Centre for Nuclear Research, A. Soltana 7, 05-400 Otwock, Poland12Laboratoire de Physique Corpusculaire, 14050 Caen cedex, France13Departimento di Fisica and INFN, Universita di Padova, 35131 Padova, Italy14Department of Physics, University of Ioannina, 45110 Ioannina, Greece15Bhabha Atomic Research Centre, Mumbai, India16INFN - Sezione di Napoli, via Cintia, 80126 Napoli, Italy17Instituut voor Kern-en Stralingsfysica, K.U. Leuven, Belgium18Rudjer Boskovic Institute, Bijenicka 54, 10000 Zagreb. Croatia19Institute of Nuclear Physics PAN, Kraków, Poland20Flerov Laboratory of Nuclear Reactions, JINR, Dubna 141980, RussiaAbstract. The exotic nucleus 8He is investigated by means of the measurement of theangular distributions of the elastic channel and the 6He and 4He fragment yields producedin the collision with a 208Pb target at two energies around the Coulomb barrier, 16 and22 MeV. The experiment was performed at the GANIL-SPIRAL facility, with the aim ofextracting information about the structure of 8He and the relevant reaction mechanisms.In this contribution, details of the experimental setup and preliminary data on elastic crosssections are reported.ae-mail: gloria.marquinez@dfa.uhu.esDOI: 10.1051/C© Owned by the authors, published by EDP Sciences, 2014,/03058 (2014)20166epjconfEPJ Web of Conferences4 6603058This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Article available at http://www.epj-conferences.org or http://dx.doi.org/10.1051/epjconf/201466030581 Introduction8He has an extended valence neutron distribution, known as neutron skin. In particular, it is thelightest skin nucleus and it has the largest neutron-to-proton ratio among the nuclei stable againstparticle emission. The scattering of 8He on gold and copper has been already investigated at GANIL[1, 2] but there is still a lack of experimental results needed to unveil the role of couplings betweenpossible reaction channels and neutron-core correlations.In comparison with the 2n-halo 6He, 8He has a more extended neutron layer whereas its bindingenergy is higher. Its binding energies for 1n (S 1n) and 2n (S 2n) systems are similar, unlike 6He, whereS 2n is appreciably less than S 1n and makes the two neutron transfer energetically favoured in collisionprocesses [3–5]. These dierences in geometry and binding energies should be reflected in the elasticand reactions cross sections in collisions at Coulomb barrier energies.In this work, preliminary experimental results for the elastic channel of the 8He+208Pb system atthe collision energies of 16 and 22 MeV are shown, together with data for the scattering of 6He withthe same target at the same energies [3, 4].2 Experimental setupThe experiment was performed in the G21 line at the SPIRAL-GANIL facility, where high qualitybeams of 8He are produced from the fragmentation of a 13C beam at 75 MeV/nucleon on a dedicatedtarget for the production of helium isotopes. Once produced and post-accelerated, the beam is driventhrough a set of collimators and beam diagnostics, towards the reaction chamber.The detection system, GLORIA (GLObal ReactIon Array) [6], was recently developed at theUniversity of Huelva for studying the structure and dynamics of exotic nuclei. It consists of twelveDSSSD detectors arranged in six particle telescopes allowing for measuring reaction fragments in acontinuous angular range between 15o and 165o, with an overall solid angle of 26.1% of 4. Eachtelescope is made of a 40  E-detector of 50 mm x 50 mm, segmented in 16 strips on each side, andby a 1 mm E-detector of the same size and segmentation.The target consisted of a self-supported foil of 208Pb with a thickness of 1mg/cm2. Its isotopiccomposition was the following: 208Pb 98.43 %, 207Pb 1.05 %, 206Pb 0.51 %, 204Pb 0.01 %. The targetwas tilted 60o with respect to the beam axis, avoiding the shadowing of detectors and allowing for thedetection of particles around 90o.3 Experimental resultsPreliminary results for the scattering of 8He on a 208Pb target at 22 MeV are shown in figure 1 in redfilled squares. For comparison, data relative to the 6He+208Pb system at the same energy is plotted ingreen [3] and blue [4] filled squares.The elastic scattering of 8He follows the trend of 6He up to 70o. At backward angles, the absorp-tion becomes even stronger for 8He than for 6He. Two calculations are also presented in the figure.The results of an Optical Model (OM) calculation using parameters obtained from the 8Li+108Pb sys-tem [7] is shown with the doted-dashed line. The solid line represents a Coupled Reaction Channels(CRC) calculation, performed with FRESCO [8]. In this calculation, in the entrance and exit channles,the OM potential from the previous OM calculation was used and the coupling with the single neutronstripping channel was included. The overlap form factors,D8Hej7He + nEandD209Pbj208Pb + nE, weretaken from [9, 10]. The comparison between both calculations reveals the importance of the couplingwith the 1n stripping channel for 8He, producing a reduction on the elastic cross section. It is alsoEPJ Web of Conferences03058-p.20 30 60 90 120 150 180θcm (deg)0.00.20.40.60.81.01.2σ(θ)/σ(θ)RuthCRC Calculation (Coupling with 1n stripping channel)OM Calculation6He+208Pb @ 22 MeV [3]8He+208Pb @ 22 MeV (PRELIMINARY)6He+208Pb @ 22 MeV [4]PRELIMINARYFigure 1. Angular distribution of the elastic cross section, normalized to the corresponding Rutherford crosssection, for the systems 8He+208Pb and 6He+208Pb at 22 MeV. See text for details.0 30 60 90 120 150 180θcm(deg)0.00.20.40.60.81.01.21.4σ(θ)/σ(θ)Ruth6He+208Pb @ 16 MeV [4]8He+208Pb @ 16 MeV (PRELIMINARY)CRC Calculation (Coupling with 1n stripping channel)OM calculationPRELIMINARYFigure 2. Angular distribution of the elastic cross section, normalized to the corresponding Rutherford crosssection, for the systems 8He+208Pb and 6He+208Pb at 16 MeV. See text for details.remarkable that the characteristic Coulomb-nuclear rainbow of the Fresnel type interference patternof light stable nuclei at this energy regime does not appear.In figure 2, preliminary results for the scattering of 8He on a 208Pb target at 16 MeV are shown inred filled squares. Also at this energy, available data for the 6He+208Pb system from [4] is plotted ingreen filled squares.INPC 201303058-p.3As found in the data at 22 MeV, at 16 MeV the absorption at backward angles, where the com-parison is possible, is even greater than for 6He. For the doted-dashed line, an OM calculation, thesame entrance channel potential as at 22 MeV have been used. The solid line, a CRC calculationcarried out in a similar way as for 22 MeV, includes the coupling to the 1n stripping channel. Also atthis energy, this coupling produces the reduction on the elastic cross section, needed to reproduce theexperimental data.4 Summary and conclusionsThe elastic scattering of 8He+208Pb has been measured at 16 and 22 MeV at SPIRAL-GANIL usingGLORIA, a detector array developed at the University of Huelva. A strong eort has been made toproperly assign the scattering angles and to calculate the solid angles subtended by each pixel of everytelescope.At 22 MeV, the angular distribution of the elastic channel follows the trend found for 6He+208Pbup to the grazing angle, where the absorption becomes greater. At 16 MeV, the absorption is alsolarger for 8He. The analysis for both energies is still ongoing.This work has been supported by the grant from the Spanish Research Council FPA-2010-22131-CO2-01, the grant from the Ministry of Science and Higher Education of Poland No. N202 033637,COPIGAL LEA, the grant EUI2009-04163432 (EUROGENESIS) from the European Science Foun-dation and the Grant VH-VI-417 from Helmholtz Association in Germany.References[1] A. Lemasson et al., Phys. Rev. C82, 044617 (2010)[2] A. Lemasson et al., Phys. Lett. B697, 454 (2011)[3] L. Acosta et al., Phys. Rev. C84, 044604 (2011)[4] A.M. Sánchez-Benítez et al., Nucl. Phys. A803, 30 (2008)[5] E.F. Aguilera et al., Phys. Rev. C63, 061603 (2001). Rapid communication.[6] G. Marquínez-Durán et al., submitted to Nucl. Inst. and Meth. A[7] J.J. Kolata et al., Phys. Rev. C65, 054616 (2002)[8] I.J. Thompson, Comput. Phys. Rep. 7, 167 (1988)[9] N. Keeley et al., Phys. Lett. B646, 222 (2007)[10] D.G. Kovar et al., Nucl. Phys. A231, 266 (1974)EPJ Web of Conferences03058-p.4

Near barrier scattering of 8He on 208Pb

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Near barrier scattering of 8He on 208Pb

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