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 70-100 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 MeVb) A/q = 2 at 500 A MeVc) 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. 2.2.3 of the EURISOL report)

A/q = 6 at 166.5 A MeV and A/q = 3 at 333 A MeV

3. 3He 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 )

86Kr + 64Ni at 25 AMeV

Solid - GEMINI, dash-SMM

Modified DIT (nucl-th/0507026, to appear in NPA):86Kr + 64Ni at 25 AMeV

solid - GEMINI, dash -SMM

86Kr + 124Sn at 25 AMeV Standard DIT ( Tassan-Got )solid - GEMINI, dash -SMM

86Kr + 124Sn at 25 AMeV Modified DIT (nucl-th/0507026):

solid - GEMINI, dash -SMM

86Kr + 112Sn at 25 AMeV Standard DIT ( Tassan-Got )

solid - GEMINI, dash -SMM

86Kr + 112Sn at 25 AMeV Modified DIT (nucl-th/0507026):

solid - GEMINI, dash -SMM Dash-dotted - SMM, s > 0.8 fm

How to reach the extremely neutron-rich nuclei ( e.g. around 78Ni ) :

- Optimize projectile-target combination

- Optimize energy. Energies lower than 20 AMeV ?

How close to e.g. 78Ni can one get with 86Kr+64Ni at 25 AMeV?

Experimental data ( 1-3 deg ) vs modified DIT + SMM

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

With 86Kr one cannot get too close to 78Ni, how about 82Se ?

Calculated yields for reaction 82Se+64Ni at 25 AMeV.

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

Reaction 82Se+64Ni - 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 ?

Observed excess of neutron-rich nuclei in reactions 124Sn+124Sn at 20 AMeV .

solid symbols - experimental data

open symbols - DIT+Gemini

dashed line - EPAX

Test of low energy data 58Ni+208Pb at 5.66 AMeV, angle-integrated data( L. Corradi et al., Phys. Rev. C 66 (2002) 24606 )

Z=22

Z=27 Z=26 Z=25

Z=24 Z=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=26 Z=25

Z=24 Z=23

Z=28

DIT calculation ( with extended radius of the nuclear potential ) for the reaction 64Ni+208Pb at 5.66 AMeV, angle-integrated data ( compared to experimental data for the reaction 58Ni+208Pb from L. Corradi et al., Phys. Rev. C 66 (2002) 24606 )

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 78Ni 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) 212701).

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 86Kr,82Se+64Ni 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 78Ni 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 78Ni

- 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

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

86Kr + 238U at 28 AMeV, Sim. vs Sim. ICF-only

82Se + 238U at 28 AMeV, Sim. vs Sim. ICF-only

18O + 181Ta at 35 AMeV, carbon isotopes

Experiment (COMBAS) PE+DIT/ICF+SMM

18O + 181Ta at 35 AMeV, beryllium isotopes

7Be - fast component, intense pre-eq emission, ICF kinematically impossible, motion along classical Coulomb trajectory ? Transparency ?

Experiment (COMBAS) PE+DIT/ICF+SMM

7Be

7Be

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)

Observed excess of neutron-rich nuclei in reactions 86Kr+64Ni 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)

ἸἩRn-R

p determines the difference

of N/Z at (Rn+R

p)/2 ( surface ) from the bulk N/Z,

correlates to isovector chemical potential

DIT (T-G) : macroscopic formula for ἸἩR

n-R

p used, values unrealistically large

but bulk N/Z dynamics described well

Modified DIT (nucl-th/0507026), 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 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 < 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 5-100 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