Reaction studies with low-energy weakly-bound
beams
Alessia Di Pietro
INFN-Laboratori Nazionali del Sud
NN 2015
Alessia Di Pietro,INFN-LNS
Outline
1. Introduction
2. Elastic scattering of weakly-bound and halo nuclei. New results of:
I. 6,7Li+64Zn
II. 11Be+197Au
III. 6He+64Zn
3. Direct reactions
4. Fusion
5. Summary and conclusions
NN 2015
Alessia Di Pietro,INFN-LNS
Exotic structures in light nuclei
halo nucleus vs normal nucleus
neutron
halo
proton
halo
clusters
10Be
neutron drip line
NN 2015
Alessia Di Pietro,INFN-LNS
Halo nuclei: e.g. 11Li, 11Be, 6He ….
Weakly bound (easy to break-up)
Easy to polarise (large B(E1) low energy strenght)
Suffer lower Coulomb barrier
Higher transfer probability
B(E1) distribution
T. Nakamura et al., Phys. Rev. Lett. 96, 252502 (2006).
T. Aumann et al., Phys. Rev. C 59, 1252 (1999).
N. Fukuda et al., Phys. Rev. C70, 054606 (2004).
NN 2015
Alessia Di Pietro,INFN-LNS
Effects of nuclear structure on collision: the elastic scattering process
NN 2015
Alessia Di Pietro,INFN-LNS
Elastic scattering of weakly bound 6,7Li on 64Zn
6Li+64Zn
7Li+64Zn
Experiment @ INFN-LNS
Above the barrier coupling to
continuum effects more important
in 6Li than in 7Li
NN 2015
Alessia Di Pietro,INFN-LNSJ.P.Fernandez-Garcia et al. submitted to PRC
Elastic scattering of halo nuclei
9,11Li+208Pb
Elab=24.3 MeV
Elab=29.8 MeV
A. Di Pietro et al. PRC 85, 054607 (2012)
M.Cubero et al., PRL109, 262701 (2012)
Long range absorption effects of both, nuclear and Coulomb
origin, accounts for suppression of elastic cross-section.
11Be+197Au
Charged particles:
- 3 telescopes DSSSD 16+16 (40µm)
+ PAD.
- 1 telescope SSSD 16 (20 µm) +
DSSSD 16+16 (300 µm).
@TRIUMF
11Be
g
beam
Calculations:
XCDCC includes a non-spherical 10Be core.
Ι 11Be(gs)> = a Ι 10Be(gs)x 2s1/2> + b Ι 10Be(2+)x 1d5/2> + c Ι 10Be(2+)x 1d3/2>
Standard CDCC
NN 2015
Ge-array TIGRESS:
-- detection of Eg=0.32 MeV
from 11Be*
SSSD
New data
6He+64Zn
@ Elab ≈ 15 and 18 MeV
LEDA
beam
NN 2015
Alessia Di Pietro,INFN-LNS
LAMP
Comparison between
4,6He+64Zn
data at two beam energies
•6He+64Zn Ec.m.=12.4 MeV PRC 69,044613(2004)
•6He+64Zn Ec.m.=13.7 MeV
4He+64Zn
The elastic angular distributions
at two different energies are
“almost” the same!
NN 2015
Alessia Di Pietro,INFN-LNS
6He+64Zn
elastic scattering
•PRC 69,044613(2004)
•PRC 69,044613(2004)
It seems that the angular distributions at Elab=13.6 MeV and 15 MeV are the same is due
to the different contribution of coupling with the trasfer channel !
NN 2015
Alessia Di Pietro,INFN-LNS
Break-up and transfer processes
Break-up
Transfer
C
C
H
P
10Be
T
P
angular distribution
T
T+n
6He+64Zn
11Be+64Zn
•PRC 84,064604(2011)
11Be+64Zn
6He+64Zn65Zn
A.M. Moro et al. PRC 89, 064609 (2014)
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Alessia Di Pietro,INFN-LNS
V. Scuderi et al. PRC 84, 064604 (2011)
Fusion
NN 2015
Alessia Di Pietro,INFN-LNS
Fusion of n-halo nuclei
● There is an effect of the halo structure on fusion
● Static effects appears to be important but not the only ones
● CF appears to be dominant over ICF
● Few data below barrier
No clear conclusions can be reached for p-halo nuclei see e.g. :
8B+58Ni - E.F. Aguilera et al.: PRL 107,092701,(2011)
8B+28Si - A.Pakou et al.: PRC87,014619,(2013)
Halo nuclei
Systematics for fusion with halo nuclei
Main ingredient:
reduce Fus(E) to eliminate static effects
Further transformation
eliminates coupling to bound
state effects
L.F. Canto et al.: NPA 821,51, (2009) ;
P.R.S. Gomes et al.: PRC 79, 027606, (2009)
J.Rangel et al.: Eur. Phys. Jour A 49, 57, (2013);
NN 2015
Alessia Di Pietro,INFN-LNS
Fusion of weakly bound nuclei with no halo structure
Systematic on heavy targets
L .F. Canto , Nucl. Phys. A 821 (2009) 51
@LNS
NN 2015
@LNS
M.Fisichella et al. to be published
Break-up dynamics in 6,7Li+144Sm, 207Pb and 209Bi
Break-up is triggered predominantly by nucleon transfer. From the relative energy of breakup fragments the time-scale of break-up was deduced and prompt break-up separated by
asymptotic break-up.
NN 2015
Alessia Di Pietro,INFN-LNS
6,7Li+64Zn
heavy residue excitation function
Ratio of H.R. cross-section
A. Di Pietro et al. PHYS. REV. C 87, 064614 (2013)
NN 2015
Alessia Di Pietro,INFN-LNS
Heavy Residue relative yields ( H.R. / tot)
Is d or a capture from 6Li important ?
● ICF
E*
 ( Ecm - Sa)x(mclu/mproj) + Q(Clu+64Zn)
● Cluster transfer E*  Qgg – Qopt
Experiment
Complete Fusion calculations
d-capture calculations
a-capture calculations
1n or 1p transfer leading to 65Zn and 65Ga can also contribute
Above barrier CF dominates
Below the barrier different processes dominate
NN 2015
A.Di Pietro et al. Phys. Rev. C 87, 064614, (2013)
Summary and conclusions
Reaction studies with halo and weakly bound beams have shown many peculiarities due to
the low binding and extended wave function :
Damping of elastic cross-section at large impact parameters due to the coupling to the
continuum. Both Coulomb and nuclear coupling contribute to the effect.
Coupling to n-transfer important in 6He elastic scattering.
Large total reaction cross-sections.
Large cross-section for transfer and breakup events. Different contribution for the different
projectiles.
With weakly bound and halo nuclei the suppression of above barrier complete fusion could
be due to break-up. Break-up triggered by nucleon transfer has been found to be more
important than direct break-up. With lighter masses the observed enhancement below the
barrier seem to be due to other processes contributing to the measured cross-section.
NN 2015
Alessia Di Pietro,INFN-LNS
RBI
Zagreb
NN 2015
Alessia Di Pietro,INFN-LNS