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Nuclear reactions induced by radioactive 6He and
8Li beams
Alinka Lépine-Szily
Instituto de Física da Universidade de São
Paulo XXXI Symposium on Nuclear Physics -
Cocoyoc 2008 Mexico
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The Nuclear Chart today
stable nuclei valley of ?-stability (less than
300 !!!)
Number of protons
TERRA INCOGNITA ( gt 5000 !!!)
known nuclei
Number of neutrons
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For unstable or radioactive nuclei

• 1. Nuclear radii dont go as A1/3
• 2. Magic Z and N numbers depend on N and Z,
  respectively
• 3. Many more bound nuclei exist than anticipated

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São Paulo Pelletron Laboratory
RIBRAS (Radioactive Ion Beams in Brazil), only
radioactive beam facility of Southern Hemisphere
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Two superconducting solenoids B6.5 T
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Superconducting solenoid

• Magnet NbTi
• Field integral 5 T.m.
• Max. central field 6.52 T
• Max. current 91.86 A
• Inductance 309 H
• Stored Energy 1.3 MJ
• Lhe vessel 250 litros
• Lhe boil-off rate 3.4 liters/day
• LN2 Vessel 130 Litros
• LN2 15 liters/day

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RIBRAS system, ability to focalize radioactive
beams up to 10MeV/n.
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Production system (primary target)
solenoid
colimator
30cm Solenoid Bore
SECONDARY BEAM
7Li
solenoid
colimator
acceptance from 2 deg to 6 deg from 2 deg to
15 deg maximum
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Selection with solenoids
B
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Detection system
50 cm
tof
y
z
Secondary target
lollipop
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Present beams at RIBRAS
present primary beam 6,7Li intensities 300 enA

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20 mm
5 mm beam spot Angular divergence 1.5 - 3 deg
5 mm
X
Paralell Plate Avalanche Counter (PPAC) X-Y
position sensitive gas detector
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Actual scientific program at RIBRAS ? Elastic
scattering and direct reactions of radioactive
and halo nuclei on light, medium-mass and heavy
targets Motivation Obtain informations on
the effect of the Coulomb and nuclear
break-up of the radioactive projectile on
the reaction cross-section at energies close
to the Coulomb barrier ? Nuclear reactions of
astrophysical interest with radioactive beams at
low energies
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Previous results Elastic sacttering of 6He on
Pb, Bi,Zn targets (LLN,ND Much larger
absorption and reaction cross-section than other
light projectiles (6,7Li, 9Be, 4He). Coulomb and
nuclear break-up of the 6He halo nucleus on
heavy and medium mass targets What about light
targets???
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Measurement of elastic scattering of 6He27Al At
RIBRAS Experimental method Radioactive 6He
beam produced by reaction 9Be(7Li,6He)10B Q
- 3.38 MeV Primary beam 7Li, intensity 300 nAe,
at energies 19, 20.5, 21 and 22
MeV Production target 16 microns 9Be
foil Radioactive beam intensity 105 pps
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Detection E-?E silicon telescopes with 300 mm2
?E 22 microns, E 150 microns
?E 50 microns, E 150 microns
Targets 27Al of 7 mg cm-2
197Au of 5 mg cm-2 ? Secondary beam energies
calculated by energy losses and confirmed by
energy calibration of the detectors 9.5, 11,
12 and 13.4 MeV ? Secondary beam intensity
determination using 197Au target (Rutherford
scattering) ?Average scattering and solid angle
determination Monte Carlo simulation with
secondary beam spot size and angular divergency
and angular distribution in the detector
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Elastic scattering of 6He beam on Au and Al
targets Energy spectra measured at 20
degrees Au
Al
6He
6He
4He
4He
4He comes from scattered contaminant 4He beam.
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6He27Al Elastic scattering
angular distributions Fit by optical
model Yields total reaction cross section at 4
energies
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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

2. Double-folding potential
v(rpa) effective zero-range nucleon-nucleon
interaction
3. Imaginary part W(r,E) NI VLE (r,E)
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Reduced quantities
To compare to other systems, as 6,7Li, 9Be and
16O on 27Al
Geometrical effects and effects related with ZpZa
are eliminated but physical effects (halo) still
remain
Elastic scattering of 6He, 9Be, 6,7Li and 16O on
27Al optical model fits using SPP
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Reduced reaction cross-sections
stable strongly bound
stable weakly bound
radioactive halo
E.A.Benjamim et al Phys. Lett. B 647 (2007) 30-35
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Conclusion the reduced reaction cross sections
of the 6He27Al system are similar to those
for the 6,7Li27Al and 9Be27Al within
experimental uncertainties. 6He is a
radio- active 2n halo nucleus, 6,7Li ,9Be are
stable, weakly bound nuclei . The cross
sections are enhanced when compared to strongly
bound projectiles as 16O on 27Al. On the
light, low Z target (27Al) the effect of the halo
on the reaction cross section is smaller than
for heavier targets.
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Elastic scattering of 4,6He and 8Li on 51V

• Elab (7Li) 30,0 MeV
• Primary target 16 µm 9Be
• Secondary beams 4,6He and 8Li
• Secondary targets Au of 5 mg/cm2
• 51V of 1.9
  mg/cm2
• Same experimental method as described previously

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Elastic scattering of 4,6He on 51V
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4 P. Gomes, Phys. Lett. B601, 20 (2004) 5 Di
Pietro, Europhys. Lett. 69, 309 (2003) 6 This
work, MS thesis V.M.Almeida 2007
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Elastic scattering of 6He and 8Li on 120Sn

• Similar experimental method and analysis
• alpha-particles from break-up are observed (not
  on 27Al and 51V targets)

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Elastic scattering of 6He on 120Sn
preliminary results PhD thesis of P.N.Faria
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Conclusion The reduced reaction cross-sections
of the 6He27Al system are similar to those for
the 6,7Li27Al and 9Be27Al within the
experimental uncertainties. On 51V, 58Ni, 64Zn
targets 4He and 6He (halo) beams have different
behaviour. On the light, low Z target (27Al)
the effect of the halo on the reaction cross
section is smaller than for heavier
targets. Coulomb break-up? 8Li is
radioactive nucleus with no halo, no enhancement
on reaction cross-section even for medium mass
targets (51V, 56Ni).
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Measurement of the H(8Li, ?)5He with 8Libeam
using the thick target method

• 8Li is a key element of the inhomogeneous Big
  Bang. It is formed by 7Li(n,?)8Li in n-rich
  environment
• The 8Li(?,n)11B, 8Li(n, ?)9Li e 8Li(d,p)9Li
  are reactions which bridge the A8 gap.
• The most important reaction to deplete the 8Li
  is the 8Li(p, ?)5He.
• Reaction performed in inverse kinematicslow cm
  energy 1-2 MeV
• PhD thesis of D.R.Mendes Jr

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9Be resonances populated in H(8Li,4He)5He
reaction
Q 14.42 MeV Elab(7Li)22 MeV and 20
MeV Elab(8Li)18.3 MeV and 16 MeV Ecm
(8Li) 2.03 MeV and 1.78 MeV Ea 20 30
MeV E(9Be) 18.92 MeV and 18.66 MeV
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Experimental method Thick secondary target
CH2 of 8 mg/cm2 stops 8Li but not 4He
adapted for transfer reaction a energy is
related to resonance energy Energy spectrum
yields excitation function
8Li
4He
E a (MeV)
Theta 23,5 Energia (7Li) 22 MeV Energia (8Li)
18,3 MeV Energia (4He Contaminate) 16,27 MeV
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Preliminary results of H(8Li,4He)5He
12C(a, a)12C
Z
H(8Li, a)5He
a
Ea
? 23,5 Energy (7Li) 22 MeV Energy (8Li) 18,3
MeV
Ea
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Possible contamination by H(7Li, a)4He reaction,
through 7Li2 beam which is also focalized by
the solenoid
12C(a, a)12C
H(7Li, a)4He
a
H(7Li, a)4He
Theta 23,5 Energy (7Li) 20 MeV Same magnetic
field , no 8Li beam, 7Li beam of same energy
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Thin target measurements CH2 target of 1.2
mg/cm2 H(8Li,4He)5He
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Angular distribution of H(8Li,4He)5He reaction
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Conclusion The reduced reaction cross-sections
of the 6He27Al system are similar to those for
the 6,7Li27Al and 9Be27Al within the
experimental uncertainties. On 51V, 58Ni, 64Zn
targets 4He and 6He (halo) beams have different
behaviour, the reaction cross-section of halo
projectile is larger than of 6,7Li and 9Be
nuclei Coulomb break-up 8Li is a
radioactive nucleus with no halo, no enhancement
on reaction cross-section even for medium mass
targets (51V, 56Ni). The cross-sections of the
reaction H(8Li,4He)5He were measured at 2
energies and more measurements will be realized.

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Whats next?

• More measurements of elastic scattering of 8Li,
  6He, 7Be, 8B on targets 208Pb, 120Sn, 58Ni,
  27Al at energies around the Coulomb barrier
• Accomplish the setup by mounting the secondary
  scattering chamber after the second solenoid
• Experiments with transfer reactions of
  astrophysical interest type (alpha,p), (alpha,n)

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• A. Lépine-Szily
• E. Benjamim (PhD)
• R. Lichtenthäler
• V. Guimarães
• L.C.Chamon
• P.R.S. Gomes (UFF-Rio de Janeiro)
• I. Padron (CUBA)
• A. Arazi (Tandar- Argentina)
• P. N. de Faria (PhD)
• R. Denke (Ms)
• D. R. Mendes Jr (PhD)
• V. Morcelle de Almeida (PhD)
• M.P.M. Assunção (Pos-doc)
• K.C.C. Pires (PhD)
• Barioni (PhD)
• O. Camargo Jr (Ms)
• J. Alcantara (Pos-doc)