Recent results on reactions with

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Recent results on reactions with radioactive
beams at RIBRAS
Alinka Lépine-Szily, and RIBRAS
collaboration
ECT workshop on Low-Energy Reaction Dynamics of
Heavy-Ions and Exotic Nuclei May 26-30, 2014,
Trento, Italy
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Outline

1. Quick description of RIBRAS
2. Elastic scattering measurements with 6He beam
3. Optical model and CDCC analysis
4. a-particle production
5. Total reaction cross sections
6. Elastic scattering and reactions on hydrogen
   target
7. R-matrix analysis and spectroscopic results

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• Major Facility for Nuclear Physics research in
  Brazil
• Tandem Accelerator Pelletron 8UD at the
• University of São Paulo - Brazil

primary beams 6Li, 7Li , 10,11B, 9Be, 12C,
16,17,18O, ...
3.0 5.0 MeV/nucleon
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RIBRAS - Radioactive Ion Beams in Brazil First
RIB facility in the Southern Hemisphere,installed
in 2004
Low energy radioactive ion beam production with
solenoid based system. University of São Paulo
Brazil

• Max field 6.5 Tesla
• versatile configuration
• persistent mode
• low LHe and LN2 consumption

First scattering chamber
2nd scattering chamber
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Production target Solid targets 9Be, LiF,12C
etc or gas targets
solenoid
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Selection with the first solenoid
angular acceptance 2 deg - 6 deg
Maximum B?1.8Tm
30msr
primary beam, transfer reactions
?E-E Si telescopes
1- primary target 2- collimator 3- Faraday
cup 4- solenoid 5- lollipop blocker 6-
collimator 7- scattering chamber, secondary
target and detectors
Beams of interest 6He, only 16, 8Li 65
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First solenoid B? selection, cocktail of
secondary beams with same B? Particles
detected in the first scattering chamber
Beam of interest 6He, only 16
Beam of interest 8Li, 66
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Double solenoids (cross-over mode)
Second solenoid helps cleaning the
secondary beam Degrader changes the Br of
the particles with different Z (q)
Solenoid -1
Solenoid - 2
Target
Degrader in first scatt.chamber
Detectors 3 new strip-detector telescopes
?E
E
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Using both solenoids with degrader between
them Particles detected in the second
scattering chamber
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Present radioactive beams at RIBRAS
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Scientific program at RIBRAS
Elastic scattering 6He 9Be,27Al,51V,58Ni,
120Sn
7Be 27Al, 51V (only first solenoid)
8Li 9Be, 51V
8B 27Al
8Li, 7Be, 9Be, 10Be on 12C
8Li p, 6He p
Transfer reactions 8Li(p,a)5He,
12C(8Li,9Li)11C Future Break-up
reactions Inelastic scattering Fusion
evaporation
(two solenoids)
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Elastic scattering measurements with 6He beam
Light, intermediate and heavy targets 9Be, 27Al,
51V, 56Ni, 120Sn
Static and dynamic effects with 6He halo nucleus
Cluster model 6He 4He 2n Weakly bound B.E.
0.973 MeV
Neutron Skin and halo static effects
Correlations and couplings between reaction
mechanisms. binding energy (breakup) effect in
elastic scattering a production Analysis using
Optical Model (São Paulo Potential-SPP),
CDCC Total reaction cross sections.
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São Paulo Potential (SPP) optical potential
with non-local interaction
L.C. Chamon, D. Pereira, M.S. Hussein, M.Alvarez,
L.Gasques, B.V. Carlson, et al. PRC 66,014610
(2002) 1. Pauli non-locality related with energy
dependence Local-equivalent potential
v is the local relative speed
2. Double-folding potential
v(rpa) effective zero-range nucleon-nucleon
interaction
3. Imaginary part W(r,E) NI VLE (r,E)
limitationsame geometry for W as for V
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6He27Al elastic scattering
First results of RIBRAS
Optical Model calculation São Paulo potential
(NI0.7 a0.56(2)normal nuclear diffuseness)
6He51V elastic scattering
Optical Model calculation São Paulo potential (N
I1.4(4) a0.67(3) larger than normal
nuclear absorption and diffuseness)
more absorption
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6He9Be elastic scattering
6He is 3 body Borromean system 6He?alpha2n
3b-CDCC.... 6He?alpha nn 4b-CDCC
Coupled Channels calculation includes low lying
excited states of 9Be and 2 state of 6He ( is
more important) Optical Potential real part Sao
Paulo potential Imaginary part Wood-Saxon
potential used for 6Li9Be
3 and 4 body CDCC calculations for 6He
(continuum discretized coupled-channel)
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6He120Sn elastic scattering
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6He 120Sn elastic scattering
Details of the coupling to the break-up channel
No-coupling to exited states, equiv to optical
model calculation
4b-CDCC only nuclear coupling
Good fit
4b-CDCC Coulomb nuclear coupling
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6He 58Ni elastic scattering
Comparison with CDCC calc. 3-body and 4-body
CDCC calculations give different cross Sections
at ?cm gt 40o. Excellent agreement with 4-body
CDCC calculation
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Polarization potentials for the 6He58Ni system
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Conclusions on angular distribution
analyses 6He 120Sn. Comparison of CDCC
calculations with and without coupling
to continuum. Need for Nuclear
Coulomb coupling to
continuum. 6He 58Ni Need for 4-body CDCC
to fit the data 6He 51V Optical Model
calculations with SPP. NI and aI has to be
increased from 0.78 to 1.4(4)
and 0.56 fm to 0.67(3) fm.
Simulates long range absorption due to breakup
coupling 6He 27Al Optical Model
calculations with SPP. NI and aI are the
same as normal stable nuclei. No
effect of breakup coupling. 6He 9Be
Comparison of CDCC calculations with and without
coupling to continuum.
Need for coupling to continuum to get good fit.
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• Production of a-particles

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Large amount of alpha particles produced in
6He120Sn and 6He9Be reactions
6He9Be
6He120Sn
6He
a -particles from projectile break-up target
break-up contaminants
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Energy spectra and angular distributions of
a-particles from 6He120Sn
collision
120Sn(6He,4He)122Sn
6He120Sn? 4He120Sn2n
a-particles resulting from 2n-transfer reaction
mostly
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• Total reaction cross sections

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PHYSICAL REVIEW C
71
, 017601 (2005)
PHYSICAL REVIEW C
71
, 017601 (2005)
Uncertainties in the comparison of fusion and
reaction cross sections of different systems
involving
Uncertainties in the comparison of fusion and
reaction cross sections of different systems
involving
Total reaction cross section can be deduced
from elastic scattering analysis.
This information is useful to investigate the
role of breakup (or other reaction
mechanisms) for weakly-bound /
exotic nuclei.
weakly bound nuclei
weakly bound nuclei
To compare fusion and total reaction cross
sections of systems with different projectiles
and targets, including halo nuclei
two recent reduction methods are available

P. R. S. Gomes, J. Lubian, I. Padron, and R. M.
Anjos
P. R. S. Gomes, J. Lubian, I. Padron, and R. M.
Anjos

ˆ



ˆ


Instituto de F
isica, Universidade Federal Fluminense, Av. Litor
anea, s
n, Gragoat
a, Niter
oi, R.J., 24210-340, Brazil
Instituto de F
isica, Universidade Federal Fluminense, Av. Litor
anea, s
n, Gragoat
a, Niter
oi, R.J., 24210-340, Brazil
/
/
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First reduction method considered
reduced energy
reduced reaction cross section
Removes Geometrical differences arising
from sizes and charges Takes into account
anomalous large radii of weakly bound / halo
nuclei
Lowering of Coulomb barrier due to these Does
not take into account change in width of fusion
barrier important
for fusion, ?? for total reaction
cross section,
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Second reduction method considered Canto et al.
J. Phys. G36, 015109

(2009)



Based on tunneling concept (Wong model)
Fusion function
RB,VB and h? radius, height, curvature
Coulomb barrier
Universal Fusion Function (UFF) should fit F(?)
if tunneling concept holds
Applied to total reaction cross section (Shorto
et al. Phys.Lett.B678,77)
However, peripheral reactions (breakup, transfer,
inelastic) do not proceed through tunneling.
Should it apply to total reaction cross
section???
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Total reaction cross sections on A120 targets
First scaling sred (6He 120Sn) enhancement
of 50 over sred ( 7Li138Ba)
Second scaling Both scalings yield 3
trends Lowest sred -gt tightly bound described
by UFF-SPP Higher sred -gt weakly bound Highest
sred -gt halo projectile
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Total reaction cross sections on A60 targets
First scaling
sred (6He 58Ni,51V,64Zn, 8B60Ni) enhancement
of 40 - 50 over sred ( 6,7,8Li A60
targets)
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Total reaction cross sections on 27Al target
First scaling No enhancement for halo nuclei
over weakly bound but over tightly bound
Second scaling No enhancement, UFF describes all
systems
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Total reaction cross sections on 12C target
First scaling Slight enhancement (15) for halo
nuclei over weakly bound
Second scaling UFF describes weakly
bound and halo systems. Enhancement over
tightly bound (0.6 UFF)
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Comparison of total reaction cross section
using first scaling A120 similar results
Coupling to Coulomb breakup and sred
highest for low energy halo nuclei, 6He and
8B A60 1.0 lt Ered lt 1.5, 40-50 enhancement
over stable, weakly bound
projectiles Ered gt 1.5 ,
enhancement reduced 27Al No
enhancement of halo over stable weakly bound at
any energy. Enhancement over tightly
bound 16O proj. 12C No error bars on sred.
Slight enhancement (15) for halo
nuclei over weakly bound at Ered gt2.5 9Be
Enhancement of 20-30 of 6He over weakly bound
at Eredgt5. Breakup of 9Be contributes.
Nuclear breakup.
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Comparison of total reaction cross section
using second scaling A120 similar results to
first scaling F(?)(6He) gt
F(?)(6,7Li) gt F(?)(4He) UFF agrees
with F(?) of 4He A system (only fusion)
Peripheral reactions are important for 6He and
weakly bound on heavy targets (Coulomb
breakup, transfer) 27Al UFF
agrees with F(?) of stable, tightly bound (16O),
weakly bound and halo projectiles
(only fusion ?) Very little peripheral
reactions even for halo and weakly bound
on 27Al target ? 12C UFF agrees with F(?)
of halo and stable weakly bound
projectiles ???? 0.6 UFF agrees with
F(?) of tightly bound 4He and 12C
projectiles ????
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Measurements with purified radioactive
beams Elastic scattering and transfer reactions
on hydrogen target
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Interest of 8Li(p,?)5He, 8Li(p,p)8Li and 8Li(p,d)
reactions

• Nuclear Physics
• Provide spectroscopic information on 9Be states
  near the p8Li threshold (16.88 MeV)
• Astrophysics
• The reaction 8Li(p,?)5He destroys the 8Li,
  preventing the access to higher mass nuclei.
• Important to measure and compare its strength
  with the branch 8Li(?,n)11B
• Previously we have measured the excitation
  function for
• 8Li(p,?)5He reaction between Ecm0.2 -2.12 MeV,
  
  
  

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2.467 MeV
a5He
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Inelastic scattering 9Be(p,p) with 180 MeV p
beam.Dixit et al, Phys.Rev. C43, 1758(1991)
Resonances with strong a structure
Our results of p(8Li,a) reaction. Mendes et
al, Phys. Rev. C86, 064321 (2012)
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Results of our previous 8Li(p,?)5He measurement

• R-matrix fits
• Spins
• Energies
• Proton and alpha widths

Astrophysical reaction rates
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The measurement of the 8Li(p,p)8Li elastic
scattering can help to constrain the resonance
parameters
 
We measured simultaneously the 8Li(p,p)8Li,
8Li(p,?)5He and 8Li(p,d)7Li reactions between
Ecm 0.8 2.0 MeV.
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Experimental method for the measurement Inverse
kinematics 8Li beam hitting thick CH2
target Primary beam 7Li, accelerated by 8UD
Pelletron tandem of São Paulo Radioactive 8Li
beam 9Be(7Li,8Li)8Be, selected by the both
solenoids of RIBRAS. Degrader between the
solenoids. Production target 16 micron 9Be
foil Radioactive beam intensity 3x105 pps (50
transmission from 1st to 2nd solenoid) Detection
deltaE(20 microns)-E(1000 microns), 300 mm2
silicon telescopes Secondary Target C1H2
7.7 mg/cm2
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Experimental method thick secondary target CH2
of 7.7 mg/cm2 Resonances populated in the
target. Energy spectrum of 4He, p, d yields
excitation function of resonance reaction
Si-telescope
4He, p
8Li beam
E2
E1
e stopping power
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Energy spectra measured on thick CH2 target at
Elab18.5 MeV
Protons hard to measure, due to low energy (Q0)
and electronic noise
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?E50µm
8Li(p,a)5He
?E20µm
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Resonances in 9Be at Ecm
0,40 0,60 1,10 1,69 1,76 MeV
Contaminant light particles subtracted (Au
target) C(8Li,p,d,a) reactions measured,
subtracted
8Li(p,p)8Li
8Li(p,a)5He
8Li(p,d)7Li
Ecm (MeV)
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7Li(d,p)8Li
Ecm(MeV)
Resonances at 1.66 and 1.76 MeV decay to 7Li
(0.477MeV), not to 7Ligs, not populated in
7Ligs(d,p)8Li. Peak shifted to lower energy.
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R-matrix analysis of three excitation functions
with AZURE
1.66 and 1.76MeV
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R-matrix analysis results (Masters
Thesis of Erich Leistenschneider 04/2014)
Black numbers Tilley et al Nuc. Phys. A745, 155
(2004) Blue numbers our analysis
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Comparison with previous work
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With parameters of the previous work
With parameters of the previous work width
for (p,d) channel
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Conclusions

• Elastic scattering measurements with 6He beam
  on light (9Be, 27Al), medium (51V,58Ni) and heavy
  (120Sn) targets.
• Optical model and CDCC analysis for medium and
  heavy targets,
• long range absorption, coupling to Coulomb
  nuclear breakup.
• Light targets 27Al, normal OM. 9Be, CDCC fits
  the data with coupling to continuum.
• Total reaction cross sections strong
  enhancement with halo projectiles on medium and
  heavy targets. Coulomb coupling
• . No enhancement on 27Al.
• Slight enhancement on 9Be and 12C targets.
  Nuclear coupling
• The simultaneous measurement of resonant elastic
  scattering 8Li(p,p)8Li, 8Li(p,a)5He and
  8Li(p,d)7Li reactions, allows to determine the
  resonance parameters of 9Be.

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Thank you

• Alinka Lépine-Szily (USP)
• and RIBRAS collaboration, as
• USP Rubens Lichtenthaler, Kelly C.C. Pires,
  Erich Leistenschneider, Valdir Guimarães, Valdir
  Scarduelli
• U. Sevilla M. Rodriguez-Gallardo and A. M.
  Moro
• ULB (Belgium) Pierre Descouvemont
• UFF (Niteroi) Djalma R. Mendes Jr, Pedro
  Neto de Faria, Paulo R.S. Gomes
• UNIFEI Viviane Morcelle
• UFBa Adriana Barioni
• GSI Juan Carlos Zamora
• TANDAR (Argentina) Andres Arazi
• USC Elisangela A. Benjamim