Reaction Mechanisms with low energy RIBs: limits and perspectives

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Reaction Mechanisms with low energy RIBs limits
and perspectives Alessia Di Pietro INFN-Laborat
ori Nazionali del Sud
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Using the radioactive beams available today one
can study reactions induced by proton or neutron
rich nuclei.
Some of such nuclei have low break-up thresholds.
In some cases like 11Li,11Be,6He, the last
weakly bound nucleon(s) form a large diffuse
HALO around a well bound core.
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? Nuclear Halo can show-up if a s o p bound state
close to the emission particle threshold.
? Low binding energy ( lt 1 MeV) of outer nucleons
make possible quantum tunneling of such nucleons
outside nuclear core.
Halo states bound states whose wave function
extends to classical forbidden region
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The study of reactions and in particular fusion
at low bombarding energies in collision induced
by halo but also weakly bound nuclei is an
important issue since it gives a great incentive
to better understand the continuum.

• Which are the theoretical expectations?
• Which the experimental methods adopted?
• Limits of the results obtained with the present
  facilities.
• Have we learned something?

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Well established that coupling of colliding
nuclei relative motion to intrinsic excitations
or other open reaction channels causes large
enhancement of fusion cross-section at
sub-barrier energies over prediction of simple
penetration models.
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Fusion excitation function for 58Ni 58,64Ni
and 64Ni 64Ni
M. Beckerman et al. Phys. Rev. Lett 45 (1980)
1472 , M. Beckerman et al. Phys. Rev. C23 (1981)
1581 M. Beckerman et al. Phys. Rev. C25 (1982)
837 12
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Time evolution of a three body system core,
halo, target.
CDCC calculationscontinuum-continuum coupling
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Present facilities where low energy beams of
halo nuclei have been used. ISOL beams ?
Louvain la Neuve 6He (no more RIBs available from
next summer) ? REX-ISOLDE 11Be ? SPIRAL 6He ?
Dubna 6He Fragmentation beams ? Riken 11Be
(after energy degradation) In flight separated
beams ? Notre Dame (6He) Available beam
intensities 105107 pps The required intensities
..... comparable with stable beam intensities!
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Experimental methods
Different techniques have been used for the
detection of the reaction products Silicon strip
arrays, ? detectors, X-ray detectors, n
detectors Problems low beam intensity and
small cross-sections ??low rate??high background
Fusion channel identification
Heavy targets ? Fission Fragments Lighter
targets ? Evaporation Residues but Direct ER
detection difficult ? Activation techniques
Detection of ? particles, X-rays or ??following
the ER radioactive decay. Alternative technique
characteristic ? rays (but very efficient
detection systems needed)
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Fusion excitation function
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Yu. E. Penionzhkevic et al. Phys. Rev. Lett. 96
(2006)162701
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? spectrum from radioactive decay
No differences of fusion cross-section are
observed among the different Be isotope induced
fusion reactions. Only statistical errors
considered.
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A strong ? particle yield due to transferB.U.
events is observed. The associated cross section
saturates 80 of total reaction cross section at
the barrier and almost all the total reaction
cross section below the barrier.
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For other systems studied.
11Be209Bi
17F208Pb
M.Mazzocco et al. EPJ A28,295(2006)
In these two cases ?R ?Fus. ?R similar to
reaction induced by well bound systems. No
strong direct reaction process contribution.
M.Romoli et al. PRC 69,064614(2004)
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M. Beckerman et al. Phys. Rev. Lett 45 (1980)
1472 , M. Beckerman et al. Phys. Rev. C23 (1981)
1581 M. Beckerman et al. Phys. Rev. C25 (1982)
837 12
M.Dasgupta et al. Phys.Rev. C70,024606,(2004)
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? Beam currents much higher then the ones
currently available (in some cases comparable
with stable beam currents). ? Possibility to
detect different reaction products (e.g.
neutrons, ?) with the new, more efficient
detection systems which will be available at
EURISOL to discriminate the different reaction
mechanisms. ? More species available.