Production of rare nuclear species with proton and heavy ion beams in various regimes Martin Veselský Institute of Physics, Slovak Academy of Sciences, Bratislava, Slovakia

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

Participant-spectator reactions at relativistic energies ( above 100 AMeV ). Applicable to both spallation reactions ( normal kinematics ) and fragmentation ( inverse kinematics ) ?

Production of exotic nuclei in spallation with proton beams ISOLDE facility ( CERN ), beam energies ~ 1 GeVA,

Production of exotic nuclei in relativistic fragmentation Separator FRS ( GSI Darmstadt ), beam energy 1 GeVA, Separátor LISE ( GANIL ), beam energy MeVA. FRS

Task 11 - Subtask 1- Heavy Ion Benefits for Driver Accelerator Driver-Beam Scenarios to be Covered 1. The three HI driver beam options described in the report of the Driver Accelerator group (App. B, Sect. 4.2 of the EURISOL report) a) A/q = 2 at 43 A MeV and A/q = 3 at 28 A MeV b) A/q = 2 at 500 A MeV c) A/q = 3 at 100 A MeV and A/q = 2 at 150 A MeV 2. The HI driver beam option described in the Target and Ion Source group (App C, Sect of the EURISOL report) A/q = 6 at A MeV and A/q = 3 at 333 A MeV 3. 3 He beam accelerated to 1 A GeV in the main linac with minor cavity modifications. All these options will be compared with the standard 1 GeV proton-driver case.

- 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 ) Nucleus-nucleus collisions at beam energies below 100 AMeV:

Experiments at fragment separator MARS ( Cyclotron Lab, Texas A&M University ).

Standard DIT ( Tassan-Got and Stefan, NPA 524 (1991) 121 ) 86 Kr + 64 Ni at 25 AMeV Solid - GEMINI, dash-SMM

Modified DIT (nucl-th/ , to appear in NPA ): 86 Kr + 64 Ni at 25 AMeV solid - GEMINI, dash -SMM

86 Kr Sn at 25 AMeV Standard DIT ( Tassan-Got ) solid - GEMINI, dash -SMM

86 Kr Sn at 25 AMeV Modified DIT (nucl-th/ ): solid - GEMINI, dash -SMM

86 Kr Sn at 25 AMeV Standard DIT ( Tassan-Got ) solid - GEMINI, dash -SMM

86 Kr Sn at 25 AMeV Modified DIT (nucl-th/ ): solid - GEMINI, dash -SMM Dash-dotted - SMM, s > 0.8 fm

How to reach the extremely neutron-rich nuclei ( e.g. around 78 Ni ) : - Optimize projectile-target combination - Optimize energy. Energies lower than 20 AMeV ?

How close to e.g. 78 Ni can one get with 86 Kr+ 64 Ni at 25 AMeV? Experimental data ( 1-3 deg ) vs modified DIT + SMM

What are the total ( angle-integrated ) cross sections ?

With 86 Kr one cannot get too close to 78 Ni, how about 82 Se ? Calculated yields for reaction 82 Se+ 64 Ni at 25 AMeV.

Calculated yields for reaction 82 Se+ 64 Ni at 15 AMeV.

Reaction 82 Se+ 64 Ni - results of simulations : - cross sections of exotic nuclei around 78 Ni at  b level - cross sections depend weakly on beam energy - with 100pnA beam, 20 mg/cm 2 target ( settings assumed in G. Souliotis et al. PLB 543 (2002) 163 ), the intensities of secondary beams around 78 Ni of /s can be expected - what is the maximum achievable current of the primary beam ?

Observed excess of neutron-rich nuclei in reactions 124 Sn+ 124 Sn at 20 AMeV. solid symbols - experimental data open symbols - DIT+Gemini dashed line - EPAX

Test of low energy data 58 Ni+ 208 Pb at 5.66 AMeV, angle-integrated data ( L. Corradi et al., Phys. Rev. C 66 (2002) ) Z=22 Z=27 Z=26Z=25 Z=24Z=23 Z=28 Experimental data vs DIT calculation ( after de-excitation )

DIT calculation with radius of nuclear potential extended by 0.75 fm. Possible explanation : deformation, neck structure ? Z=22 Z=27 Z=26Z=25 Z=24Z=23 Z=28

DIT calculation ( with extended radius of the nuclear potential ) for the reaction 64 Ni+ 208 Pb at 5.66 AMeV, angle-integrated data ( compared to experimental data for the reaction 58 Ni+ 208 Pb from L. Corradi et al., Phys. Rev. C 66 (2002) )

Isoscaling in nuclear processes M.B. Tsang et al., PRL 86(2001)5023 G. Souliotis et al., PRC 68(2003)24605 M. Veselský et al., PRC 69(2004)44607

Comparison of various scenarios - production cross sections compared, others factors such as target thickness, extraction efficiencies are important - region around 78 Ni selected as a test case - spallation - GSI model used ( statistical abrasion-ablasion + de-excitation/fission ) - fragmentation - cross sections calculated using EPAX-2, optimized for each isotope over all stable beams

Calculated ( GSI model ) cross sections for 1 GeV proton beam colliding with U, Th, W and La (solid, dashed, dash-dotted and dotted lines, respectively).

Calculated ( GSI model ) cross sections for 1 GeV proton beam colliding with U (solid line), compared to cross sections measured at GSI (P. Armbruster et al., PRL 93 (2004) ).

Calculated cross sections for 1 GeV proton beam colliding with U (solid line), compared to the optimal fragmentation cross sections (dashed line ), calculated with EPAX-2 for each nuclide separately using all  -stable beams.

Calculated cross sections for 1 GeV proton beam colliding with La (solid line), compared to fragmentation cross sections, calculated with EPAX-2 using La beam and using all  -stable beams ( dash-dotted and dashed lines ).

Calculated cross sections for 1 GeV proton beam colliding with U (solid line), compared to the calculated inclusive cross sections for reactions 86 Kr, 82 Se+ 64 Ni at 25 AMeV (dashed and dash-dotted line, respectively) and optimal fragmentation cross sections (dotted line).

Relative cross sections calculated with EPAX-2 for each nuclide separately using all  -stable beams in one-step and two-step scenarios (solid and dashed line, respectively).

Contour plot of fragmentation cross sections (dashed lines ), calculated for 78 Ni with EPAX-2 using both stable ( dash-dotted line ) and unstable beams.

Conclusions : - spallation/fission, fragmentation and peripheral ( deep-inelastic ) collisions were considered as possible candidates for production of exotic ( neutron-rich ) nuclei around 78 Ni - U-target is optimal for spallation/fission with 1 GeV proton beam - cross sections in peripheral ( deep-inelastic ) collisions largest of all for the most n-rich nuclei, technically plausible to explore them ? - systematic cross sections data from peripheral ( deep-inelastic ) collisions are necessary at both Fermi-energy domain and low energies

Extras

86 Kr + 64 Ni at 25 AMeV, Exp. vs. Sim. vs Sim. ICF-only

86 Kr U at 28 AMeV, Sim. vs Sim. ICF-only

82 Se U at 28 AMeV, Sim. vs Sim. ICF-only

18 O Ta at 35 AMeV, carbon isotopes Experiment (COMBAS) PE+DIT/ICF+SMM

18 O Ta at 35 AMeV, beryllium isotopes 7 Be - fast component, intense pre-eq emission, ICF kinematically impossible, motion along classical Coulomb trajectory ? Transparency ? Experiment (COMBAS) PE+DIT/ICF+SMM 7 Be

EURISOL - 6FP Project "EURISOL Design Study" started in Feb 2005 ( MV/Bratislava involved ) - 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)

Observed excess of neutron-rich nuclei in reactions 86 Kr+ 64 Ni at 25 AMeV. solid symbols - experimental data open symbols - DIT+Gemini dashed line - EPAX

Correlation of skin thickness to isovector chemical potential (V. Kolomietz et al, PRC 64(2001)024315, extended Thomas-Fermi calculation)  R n -R p determines the difference of N/Z at (R n +R p )/2 ( surface ) from the bulk N/Z, correlates to isovector chemical potential  DIT (T-G) : macroscopic formula for  R n -R p used, values unrealistically large but bulk N/Z dynamics described well

Modified DIT (nucl-th/ ), phenomenological correction, effect of shell structure on nuclear periphery ( assuming validity of the R n -R p 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 )

Conclusions 86 Kr + 64 Ni, 112,124 Sn 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 112 Sn stronger Coulomb interaction supresses the effect of isospin asymmetry at nuclear periphery at s < 1 fm

Conclusions - low energy - deep-inelastic collisions a dominant mechanism for production of exotic nuclei - systematic cross section data needed

Fragment separator VAMOS ( GANIL Caen ) - angular acceptance 9 deg for beam energies AMeV.

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