Production of neutronrich nuclei in peripheral collisions

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Production of neutron-rich nuclei in peripheral
collisions Martin Veselský Institute of
Physics of Slovak Academy of Sciences,
Bratislava, Slovakia
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Exotic nuclei - only 2500 out of approx 6000
possible nuclei known - large region of very
neutron-rich nuclei still unknown - region of
superheavy nuclei Physics questions -
properties of nuclear surface ( neutron skin
) - nuclear astrophysics ( r-process ) -
hyperheavy nuclei, nuclear molecules
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FRS
Production of exotic nuclei in relativistic
fragmentation Separator FRS ( GSI Darmstadt ),
beam energy 1 GeVA, Separátor LISE ( GANIL ),
beam energy 70-100 MeVA.
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Participant-spectator reactions at relativistic
energies ( above 100 AMeV )
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Peripheral nucleus-nucleus collisions - binary
collisions, intense nucleon exchange -
production of exotic nuclei, access to the limits
of nuclear stability ?
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Experiments at fragment separator MARS (
Cyclotron Lab, Texas AM University ).
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Observed excess of neutron-rich nuclei in
reactions 86Kr64Ni at 25 AMeV. solid symbols
- experimental data open symbols -
DITGemini dashed line - EPAX
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Observed excess of neutron-rich nuclei in
reactions 124Sn124Sn at 20 AMeV . solid
symbols - experimental data open symbols -
DITGemini dashed line - EPAX
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Nucleus-nucleus collisions at beam energies
below 100 AMeV
- peripheral elastic and quasi-elastic ( QE )
collisions - semi-peripheral deep-inelastic
collisions ( DIT ) collisions - incomplete (
ICF ) and complete ( CF ) fusion in central
collisions - pre-equilibrium emision typically
preceding ICF/CF and DIT ( detailed description
in M. Veselský, Nuclear Physics A 705(2002)191
)
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Peripheral collisions ( M. Veselsky, G.
Souliotis, nucl-th/0507026 ) reactions 86Kr
64Ni, 112,124Sn at 25 AMeV effect of nuclear
periphery ( neutron skin ? )
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86Kr 64Ni at 25 AMeV
Standard DIT ( Tassan-Got and Stefan, NPA 524
(1991) 121 )
Solid - GEMINI, dash-SMM
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Correlation of skin thickness to isovector
chemical potential (V. Kolomietz et al, PRC
64(2001)024315, extended Thomas-Fermi
calculation)
- ??Rn-Rp determines the difference of N/Z at
(RnRp)/2 ( surface ) from the bulk N/Z,
correlates to isovector chemical potential
- DIT (T-G) macroscopic formula for ??Rn-Rp
used, values unrealistically large but bulk N/Z
dynamics described well
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Modified DIT (nucl-th/0507026), phenomenological
correction, effect of shell structure on nuclear
periphery ( assuming validity of the Rn-Rp vs
?n-?p correlation ) and thus on transfer
probability estimated as
where ?S... S...exp - S...mac , ? is a free
parameter ( ? 0.53 determined as optimal value
), s 0 fm ( only non-overlapping
configurations considered )
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86Kr 64Ni at 25 AMeV
Modified DIT (nucl-th/0507026)
solid - GEMINI, dash -SMM
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86Kr 124Sn at 25 AMeV
Standard DIT ( Tassan-Got )
solid - GEMINI, dash -SMM
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86Kr 124Sn at 25 AMeV
Modified DIT (nucl-th/0507026)
solid - GEMINI, dash -SMM
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86Kr 112Sn at 25 AMeV
Standard DIT ( Tassan-Got )
solid - GEMINI, dash -SMM
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86Kr 112Sn at 25 AMeV
Modified DIT (nucl-th/0507026)
Dash-dotted - SMM, s 0.8 fm
solid - GEMINI, dash -SMM
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Conclusions 86Kr 64Ni, 112,124Sn at 25 AMeV -
a correction to DIT describes the effect of
isospin asymmetry at nuclear periphery -
inversion of the bulk isospin flow due to
microscopic structure at nuclear periphery
- consistent parameters ? for all reactions -
SMM reproduces the yields of n-rich species well
while overestimating the yields of ?-stable
isotopes close to the projectile - GEMINI
typically overestimates the width of mass
distributions - for p-rich target 112Sn
stronger Coulomb interaction supresses the
effect of isospin asymmetry at nuclear periphery
at s
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Central collisions reaction 124Sn27Al at 20
AMeV ( M. Veselsky et al., NPA 724 (2003) 431
) ( test of the model description of central
collisions ( M. Veselsky, NPA 705 (2002) 193 ) )
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Model description ( M. Veselsky, NPA 705 (2001)
191 ) - classical Coulomb trajectories
assumed - pre-eq. emission multiplicity
proportional to maximum overlap -
participant-spectator scenario assumed at maximum
overlap - incomplete fusion of the participant
zone with one of the spectators
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PEDIT/ICFGEMINI
PEDIT/ICFSMM
124Sn27Al at 20 AMeV
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Single source 144Nd, E310 MeV, v0.17c
A65-75
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How to reach the extremely neutron-rich nuclei
- Optimize projectile-target combination -
Optimize energy. Energies lower than 20 AMeV ?
- Two-step scenario ?
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How close to e.g. 78Ni can one get with 86Kr64Ni
at 25 AMeV?
Experimental data ( 1-3 deg ) vs modified DIT
SMM
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What are the total ( angle-integrated ) cross
sections ?
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With 86Kr one cannot get close to 78Ni, how about
82Se ?
Calculated yields for reaction 82Se64Ni at 25
AMeV.
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Calculated yields for reaction 82Se64Ni at 15
AMeV.
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Reaction 82Se64Ni - results of simulations -
cross sections of exotic nuclei around 78Ni at
0.1 - 1 ?b level - cross sections depend
weakly on beam energy - with 100pnA beam, 20
mg/cm2 target ( settings assumed in G. Souliotis
et al. PLB 543 (2002) 163 ), the intensities of
secondary beams around 78Ni of 10 - 100 /s can
be expected - what is the maximum achievable
current of the primary beam ?
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Test of low energy data 58Ni208Pb at 5.66 AMeV,
angle-integrated data ( L. Corradi et al., Phys.
Rev. C 66 (2002) 24606 )
Z26
Z25
Z28
Z27
Z22
Z24
Z23
Experimental data vs DIT calculation ( after
de-excitation )
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DIT calculation with radius of nuclear potential
extended by 0.75 fm. Possible explanation
deformation, neck structure ?
Z26
Z25
Z28
Z27
Z22
Z24
Z23
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DIT calculation ( with extended radius of the
nuclear potential ) for the reaction 64Ni208Pb
at 5.66 AMeV, angle-integrated data ( compared to
experimental data for the reaction 58Ni208Pb
from L. Corradi et al., Phys. Rev. C 66 (2002)
24606 )
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M.B. Tsang et al., PRL 86(2001)5023
G. Souliotis et al., PRC 68(2003)24605
Isoscaling in nuclear processes
M. Veselský et al., PRC 69(2004)44607
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Conclusions - low energy - deep-inelastic
collisions a dominant mechanism for production
of exotic nuclei - systematic cross section
data needed
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Fragment separator VAMOS ( GANIL Caen ) -
angular acceptance 9 deg for beam energies 5-100
AMeV.
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Production of extremely neutron-rich nuclei -
two-step process. Experiment approved at GSI ( a
part of EURISOL effort ).
Primary target
Separation of secondary beam
Secondary target
Identification of final products
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Two-step scenario with primary or secondary
reactions around Fermi energy or at low energies
?
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Conclusions - peripheral deep-inelastic
collisions are a promising candidate for
production of exotic ( neutron-rich ) nuclei -
systematic cross sections data are necessary at
both Fermi-energy domain and low energies in
order to determine optimal projectile-target
combination and beam energy - production of
beams of exotic nuclei possible either with a
stable beams or within a two-step scenario -
achievable intensities depend crucially on
available beam currents
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Extras
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Experiment (COMBAS)
PEDIT/ICFSMM
18O 181Ta at 35 AMeV, carbon isotopes
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Experiment (COMBAS)
PEDIT/ICFSMM
7Be
7Be
18O 181Ta at 35 AMeV, beryllium isotopes 7Be -
fast component, intense pre-eq emission, ICF
kinematically impossible, motion along classical
Coulomb trajectory ? Transparency ?
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EURISOL - 6FP Project "EURISOL Design Study"
started in Feb 2005 ( MV/Bratislava involved
) http//www.eurisol-ds.lnl.infn.it/ -
theoretical and experimental studies of
production mechanisms are planned - open
question - Heavy Ion capability for driver
accelerator - yes or no ? - selection of the
key experiment(s)
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