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Proceedings ArticleDOI

Exotic Nuclei in South America

05 Aug 2010-Vol. 1265, Iss: 1, pp 27-30

Abstract: The Radioactive Ion Beams in Brasil (RIBRAS) is described. Experiments using radioactive secondary beams of light rare isotopes such as 6He, 7Be, 8Li on several targets have been performed and the results are presented.

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AIP Conference Proceedings 1265, 27 (2010); https://doi.org/10.1063/1.3480185 1265, 27
© 2010 American Institute of Physics.
Exotic Nuclei in South America
Cite as: AIP Conference Proceedings 1265, 27 (2010); https://
doi.org/10.1063/1.3480185
Published Online: 05 August 2010
R. Lichtenthäler, A. Lépine-Szily, V. Guimarães, P. N. de Faria, D. R. Mendes, K. C. C.
Pires, V. Morcelle, A. Barioni, M. C. Morais, R. Pampa Condori, M. Assunção, A. M.
Moro, M. Rodríguez-Gallardo, and A. Arazi

Exotic Nuclei in South America
R. Lichtenthäler
a
, A. Lépine-Szily
a
, V. Guimarães
a
, P.N. de Faria
a
, D.R.
Mendes Jr.
a
, K.C.C. Pires
a
, V.
Morcelle
a
, A. Barioni
a
, M.C. Morais
a
, R.
Pampa Condori,
a
M. Assunção
e
, A.M. Moro
b
, M. Rodríguez-Gallardo
b,c
,A. Arazi
d
a
Instituto de Fisica da USP, São Paulo, Brazil, C.P. 66318, 05314-970
b
Departamento de FAMN, Universidad de Sevilla, Apdo. 1065, E-41080, Sevilla, Spain
c
Instituto de Estructura de la Materia, CSIC, Serrano 123, E-28006 Madrid, Spain
d
Laboratorio TANDAR, Comision Nacional de Energia Atomica, Argentina
e
Departamento de Ciencias Exatas e da Terra, Unifesp, Campus de Diadema, São Paulo, Brazil
Abstract. The Radioactive Ion Beams in Brasil (RIBRAS) is described. Experiments using
radioactive secondary beams of light rare isotopes such as
6
He,
7
Be,
8
Li on several targets have
been performed and the results are presented.
Keywords: Rare isotopes, Radioactive Beams, Elastic Scattering, neutron halo, transfer
reactions
PACS: 25.60-t,25.60.Bx
The study of reaction induced by secondary beams of rare isotopes is one of the most
active fields in Nuclear Physics nowadays. Nuclei far from the line of beta stability are
called exotic nuclei and present unusual features compared to the stable isobars.
Neutron rich nuclei like
6,8
He present a cluster like structure formed by an alpha core
and a “halo” of neutrons which extends over large distances from the core and with
densities much lower than the normal nuclear matter. The weakly bound neutrons
enhances the total reaction cross sections of those exotic nuclei and the possible
presence of such rare isotopes in astrophysical sites like supernovas explosions and the
Big-Bang nucleosynthesis could have consequences in the formation of the stable
known elements.
RIBRAS is presently the only experimental equipment in South America capable of
producing secondary beams of rare isotopes. It consists of two superconducting
solenoids, presently installed in one of the beam lines of the 8 MV Pelletron Tandem
27
CREDIT LINE (BELOW) TO BE INSERTED ON THE FIRST PAGE OF EACH PAPER
EXCEPT THE ARTICLES ON PP. 144 – 147 and 178 - 179
CP1265, VIII Latin American Symposium on Nuclear Physics and Applications
edited by R. Alcaron, H. F. Arellano, P. L. Cole, and A. J. Kreiner
© 2010 American Institute of Physics 978-0-7354-0814-2/10/$30.00
CREDIT LINE (BELOW) TO BE INSERTED ONLY ON THE FIRST PAGE OF THE
ARTICLES ON PP. 144 – 147 and 178 - 179
CP1265, VIII Latin American Symposium on Nuclear Physics and Applications
edited by R. Alcaron, H. F. Arellano, P. L. Cole, and A. J. Kreiner
2010 American Institute of Physics 978-0-7354-0814-2/10/$30.00

accelerator of the University of São Paulo. The exotic nuclei are produced in the
collision between the primary beam of the Pelletron Accelerator and the primary target,
placed just before the first solenoid (see figure I). The first solenoid focus the
secondary beam on a secondary target where the reaction of interest takes place. The
7
Li
of 3-5 MeV/A and a
9
Be (~12
µ
m) are the standard primary beam and primary target to
produce
6
He and
8
Li secondary beams beams via the one proton stripping
9
Be(
7
Li,
6
He)
and one neutron pickup
9
Be(
7
Li,
8
Li) reactions. A
3
He gas primary target is used to
produce the
8
B and
7
Be beams by the
3
He(
6
Li,
8
B) and
3
He(
7
Li,
7
Be) reactions. The
primary beam cross the primary target (see label (1) in Figure 1) and is collected in the
Faraday cup (3). The secondary particles produced in the primary target are collected by
the first solenoid within a cone between
oo
62
θ
defined by the Faraday cup and
the collimator (2). The acceptance solid angle of the system is 30 msr. The first solenoid
makes a magnetic-rigidity selection to focus the secondary beam in the secondary target
position (7). Unwanted secondary particles are stopped in the blocker (5) and collimator
(6). A second identical solenoid is mounted after the target (7) and will allow an
additional filtering improving the purity of the secondary beams. Presently we operate
only with the first solenoid.
FIGURE 1. Scheme of the first solenoid RIBRAS system. –1-primary target,
2-collimator, 3-Farady cup, 4-solenoid, 5-unwanted-beam blocker, 6-collimator, 7-secondary target and
detectors.
28

This system allows the production of beams of the light nuclei mentioned above with
intensities of 10
4
to 10
6
pps and energies in the range 1-5 MeV/A.
The research performed at RIBRAS consists basically of elastic scattering and nucleon
transfer reactions studies at low energies, using light exotic beams such as
6
He,
8
Li and
7
Be. The elastic scattering allows the study of the interacting potential and the total
reaction cross section. We have been developing this program using the medium-heavy
target
120
Sn [2], medium mass targets such as
58
Ni and
51
V [3] and lighter targets such as
27
Al [4],
12
C[5,6] and
9
Be[7,8]. The sistematic study using targets of different atomic
numbers allows the investigation of the interplay between the Coulomb and nuclear
interactions in the collision. Due to the fact that the exotic nuclei are weakly bound, the
breakup and the neutron transfer reactions become important channels even at energies
below the Coulomb barrier, strongly coupled with the elastic channel. As a
consequence, the usual optical potentials fail to reproduce the elastic angular
distributions and the coupling to the continuum has to be considered explicitly via
CDCC calculations[8,15]. The presence of a long range imaginary potential is a feature
present in the scattering of
6
He on heavy targets and is probably due to the projectile
breakup in the Coulomb field of the target.
The total reaction cross section of exotic projetiles presents an enhancement compared
to stable isobar projectiles in identical heavy targets [2,13].
To compare the reaction cross sections of different systems at different energies, it is
convenient to rescale the cross sections and energies in order to overcome trivial effects
due to the different sizes and energies with respect to the Coulomb barrier [10,11]
For lighter systems such as
6
He+
27
Al,
6
He+
12
C and
6
He+
9
Be[7,8] situation is still
inconclusive [12]. There are some indications that the enhancement observed in
6
He+
heavy targets could be smaller for lighter systems such as the
6
He+
27
Al[4] and
8
B+
12
C
[6], although a larger reduced reaction cross section has been obtained in some analysis
[9].
Another interesting field opened by the advent of exotic secondary beams is the
spectroscopic study of nuclei out of the line of stability and its consequences in
reactions of astrophysical interest. The proton transfer
12
C(
8
Li,
9
Be)
11
B reaction has been
measured at RIBRAS [5,6]. As the vertex
>< CB
1211
|
is known, this reaction provides
information of the
>< BeLi
98
|
spectroscopic factor, which normalizes the radiative
capture
BepLi
98
+
cross section.
29

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Proceedings ArticleDOI
29 Feb 2012
Abstract: Experiments using secondary beams of light rare isotopes such as 6He, 7Be and 8Li have been performed at the Radioactive Ion Beams Facility (RIBRAS) installed in the University of Sao Paulo, Brazil. A description of some results that have been obtained over the last years is presented.