recent results on reactions with radioactive beams at ribras
DESCRIPTION
Recent results on reactions with radioactive beams at RIBRAS. Alinka Lépine-Szily, and RIBRAS collaboration. ECT* workshop on Low-Energy Reaction Dynamics of Heavy-Ions and Exotic Nuclei May 26-30, 2014, Trento, Italy. Outline. Quick description of RIBRAS - PowerPoint PPT PresentationTRANSCRIPT
Recent results on reactions withradioactive beams at RIBRAS
Alinka Lépine-Szily, andRIBRAS collaboration
ECT* workshop on Low-Energy Reaction Dynamics of Heavy-Ions and Exotic Nuclei May 26-30, 2014, Trento, Italy
1. Quick description of RIBRAS
2. Elastic scattering measurements with 6He beam
3. Optical model and CDCC analysis
4. α-particle production
5. Total reaction cross sections
6. Elastic scattering and reactions on hydrogen target
7. R-matrix analysis and spectroscopic results
Outline
Major Facility for Nuclear Physics research in BrazilTandem Accelerator – Pelletron 8UD at the
University of São Paulo - Brazil
3.0 – 5.0 MeV/nucleon
primary beams:
6Li, 7Li , 10,11B, 9Be, 12C, 16,17,18O, ...
Low energy radioactive ion beam production with solenoid based system.University of São Paulo – Brazil
RIBRAS - Radioactive Ion Beams in BrazilFirst RIB facility in the Southern Hemisphere,installed in 2004
Max field 6.5 Tesla versatile configuration persistent mode low LHe and LN2 consumption
First scattering chamber
2nd scattering chamber
1- primary target 2- collimator3- Faraday cup4- solenoid5- lollipop blocker6- collimator7- scattering chamber, secondary target and detectors
Selection with the first solenoidSelection with the first solenoid
primary beam,transfer reactions
angular acceptance2 deg - 6 deg
30msrq
mE=
q
mv=Bρ
2 Maximum Bρ=1.8Tm
ΔE-E Sitelescopes
Beams of interest: 6He, only 16%, 8Li 65%
Double solenoids (cross-over mode)
Second solenoid helps cleaning the secondary beam: Degrader changes the B of the particles with different Z (q)
Solenoid -1 Solenoid - 2
Degrader in first scatt.chamber
Target
Detectors3 new strip-detector telescopes
2
2
q
AEkB
E
ΔE
secondary ion reaction intensity / 1A of primary beam
6He 9Be(7Li,6He) 2 x 105 p/s 8Li 9Be(7Li,8Li) 106 p/s 7Be 3He(6Li,7Be) 6x105 p/s 7Be 6Li(7Li,7Be) 105 p/s 10Be 9Be(11B,10Be) 2 x 103 p/s 8B 3He(6Li,8B) 104 p/s 18F 12C(17O,18F) 104 p/s 17F 3He(16O,17F)d *
Present radioactive beams at RIBRAS
Scientific program at RIBRAS
Elastic scattering: 6He +9Be,27Al,51V,58Ni,120Sn 7Be + 27Al, 51V (only first solenoid) 8Li + 9Be, 51V 8B + 27Al 8Li, 7Be, 9Be, 10Be on 12C 8Li + p, 6He + p
Transfer reactions: 8Li(p,α)5He, 12C(8Li,9Li)11C
Future:Break-up reactionsInelastic scatteringFusion – evaporation
(two solenoids)
Elastic scattering measurements with 6He beam
Light, intermediate and heavy targets: 9Be, 27Al, 51V, 56Ni, 120Sn
Static and dynamic effects with 6He halo nucleus
Cluster model6He = 4He +2n
Weakly bound B.E.= 0.973 MeV
Neutron Skin and halo: static effects Correlations and couplings between reaction mechanisms. binding energy (breakup) effect in elastic scattering: α production
Analysis using Optical Model (São Paulo Potential-SPP), CDCC
Total reaction cross sections.
São Paulo Potential (SPP) – optical potential with non-local interaction
L.C. Chamon, D. Pereira, M.S. Hussein, M.Alvarez, L.Gasques, B.V. Carlson, et al. PRC 66,014610 (2002) 1. Pauli non-locality related with energy dependence
Local-equivalent potential : ]/4[ 22
)(),( cvfoldLE erVErV
2. Double-folding potential :
)(v)()()( paaappapfold rrrrdrdrV
v(rpa): effective zero-range nucleon-nucleon interaction
)()(v paopa rVr
3. Imaginary part : W(r,E)= NI VLE (r,E) limitation:same geometry for W as for V
v is the local relative speed
6He+27Al elastic scattering
Optical Model calculationSão Paulo potential (NI~0.7a=0.56(2)=normal nuclear diffuseness)
First results of RIBRAS
6He+51V elastic scattering
more absorption
Optical Model calculationSão Paulo potential (N I~1.4(4)a=0.67(3) larger than normal nuclearabsorption and diffuseness)
6He+9Be elastic scattering
Coupled Channels calculation: includes low lying excited states of 9Be and 2+ state of 6He ( is more important)Optical Potential: real part: Sao Paulo potentialImaginary part: Wood-Saxon potential used for 6Li+9Be
3 and 4 body CDCC calculations for 6He (continuum discretized coupled-channel)
6He is 3 body Borromean system 6Healpha+2n 3b-CDCC....6Healpha +n+n 4b-CDCC
)(4 mbCDCCbreaction
)(mbbreakup
6He+120Sn elastic scattering
No-coupling to exited states, equiv to optical model calculation
4b-CDCC Coulomb + nuclear coupling
Details of the coupling to the break-up channel
4b-CDCC only nuclear coupling
6He + 120Sn elastic scattering
Good fit
6He + 58Ni elastic scattering
Comparison with CDCC calc.
3-body and 4-body CDCCcalculations give different crossSections at θcm > 40o.
Excellent agreement with4-body CDCC calculation
Conclusions on angular distribution analyses:
6He + 120Sn. Comparison of CDCC calculations with and without coupling to continuum. Need for Nuclear + Coulomb coupling to continuum.
6He + 58Ni Need for 4-body CDCC to fit the data
6He + 51V Optical Model calculations with SPP. NI and aI has to be increased from 0.78 to 1.4(4) and 0.56 fm to 0.67(3) fm. Simulates long range absorption due to breakup coupling
6He + 27Al Optical Model calculations with SPP. NI and aI are the same as normal stable nuclei. No effect of breakup coupling.
6He + 9Be Comparison of CDCC calculations with and without coupling to continuum. Need for coupling to continuum to get good fit.
Production of α-particles
Large amount of alpha particles produced in 6He+120Sn and 6He+9Be reactions
E
6He
6He+9Be6He+120Sn
α -particles from projectile break-up + target break-up + contaminants
Energy spectra and angular distributions of α-particles from 6He+120Sn collision
6He+120Sn4He+120Sn+2n
120Sn(6He,4He)122Sn
α-particles resulting from 2n-transfer reaction mostly
Total reaction cross sections
Total reaction cross section can be deduced from elastic scattering analysis.
To compare fusion and total reaction cross sections of systems with different projectiles and targets, including halo nuclei
two recent reduction methods are available:
This information is useful to investigate the role of breakup (or other reaction mechanisms) for weakly-bound / exotic nuclei.
reduced energy
fm
MeV
ZZ
AAEE
ap
apcm
redcm
3/13/1
reduced reaction cross section
)(23/13/1mb
AA ap
RredR
Removes: Geometrical differences arising from sizes and charges
Takes into account: anomalous large radii of weakly bound / halo nuclei Lowering of Coulomb barrier due to these
Does not take into account: change in width of fusion barrier: important for fusion, ?? for total reaction cross section,
First reduction method considered:
Second reduction method considered: Canto et al. J. Phys. G36, 015109 (2009)
Fusion function
Based on tunneling concept (Wong model)
RB,VB and hω = radius, height, curvature Coulomb barrier
Universal Fusion Function (UFF) shouldfit F(χ) if tunneling concept holds
However, peripheral reactions (breakup, transfer, inelastic) do not proceed through tunneling. Should it apply to total reaction cross section???
Applied to total reaction cross section (Shorto et al. Phys.Lett.B678,77)
First scaling:
σred (6He +120Sn): enhancement
of ~ 50% over σred ( 7Li+138Ba)
Second scaling:
Both scalings yield 3 trends:
Lowest σred -> tightly bound
described by UFF-SPP
Higher σred -> weakly bound
Highest σred -> halo projectile
Total reaction cross sectionson A~120 targets
Total reaction cross sections on A~60 targetsFirst scaling
σred (6He + 58Ni,51V,64Zn, 8B+60Ni): enhancement
of ~ 40 - 50% over σred ( 6,7,8Li + A~60 targets)
Total reaction cross sections on 27Al target
First scalingNo enhancement for halo nuclei over weakly boundbut over tightly bound
Second scaling
No enhancement, UFFdescribes all systems
Total reaction cross sections on 12C target
First scaling
Slight enhancement (15%)for halo nuclei over weakly bound
Second scaling
UFF describes weakly bound and halo systems.Enhancement over tightlybound (0.6 UFF)
Comparison of total reaction cross section using first scaling:
A~120 similar results Coupling to Coulomb breakupand σred highest for low energy halo nuclei, 6He and 8BA~60 1.0 < Ered < 1.5, 40-50% enhancement over stable, weakly bound projectiles Ered > 1.5 , enhancement reduced 27Al No enhancement of halo over stable weakly bound at any energy. Enhancement over tightly bound 16O proj.
12C No error bars on σred. Slight enhancement (15%) for halo nuclei over weakly bound at Ered >2.5 9Be Enhancement of 20-30% of 6He over weakly bound at Ered>5. Breakup of 9Be contributes. Nuclear breakup.
Comparison of total reaction cross section using second scaling :
A~120 similar results to first scaling F(χ)(6He) > F(χ)(6,7Li) > F(χ)(4He) UFF agrees with F(χ) of 4He +A system (only fusion) Peripheral reactions are important for 6He and weakly bound on heavy targets (Coulomb breakup, transfer) 27Al UFF agrees with F(χ) of stable, tightly bound (16O), weakly bound and halo projectiles (only fusion ?) Very little peripheral reactions even for halo and weakly bound on 27Al target ?12C UFF agrees with F(χ) of halo and stable weakly bound projectiles ???? 0.6 UFF agrees with F(χ) of tightly bound 4He and 12C projectiles ????
Measurements with purified radioactive beams:
Elastic scattering and transfer reactions on hydrogen target
Nuclear Physics:• Provide spectroscopic information on 9Be states near the p+8Li threshold (16.88 MeV)
Astrophysics: • The reaction 8Li(p,)5He destroys the 8Li, preventing the access to higher mass nuclei.•Important to measure and compare its strength with the branch 8Li(,n)11B
Previously we have measured the excitation function for 8Li(p,)5He reaction between Ecm=0.2 -2.12 MeV,
Interest of 8Li(p,)5He, 8Li(p,p)8Li and 8Li(p,d) reactions:
α+5He
2.467 MeV
Inelastic scattering 9Be(p,p´) with 180 MeV p beam.Dixit et al, Phys.Rev. C43, 1758(1991)
Resonances with strong αstructure
Our results of p(8Li,α) reaction. Mendes et al,Phys. Rev. C86, 064321(2012)
R-matrix fits:•Spins•Energies•Proton and alpha widths
Astrophysical reaction rates
Results of our previous 8Li(p,)5He measurement:
39
The measurement of the 8Li(p,p)8Li elastic scattering can help to constrain the resonance parameters
We measured simultaneously the 8Li(p,p)8Li, 8Li(p,)5He and 8Li(p,d)7Li reactions between Ecm = 0.8 – 2.0 MeV.
Experimental method for the measurement:
Inverse kinematics: 8Li beam hitting thick CH2 target
Primary beam 7Li, accelerated by 8UD Pelletron tandem of São Paulo
Radioactive 8Li beam 9Be(7Li,8Li)8Be, selected by the both solenoids of RIBRAS. Degrader between the solenoids.
Production target: 16 micron 9Be foil
Radioactive beam intensity: 3x105 pps (50% transmission from 1st to 2nd solenoid)
Detection: deltaE(20 microns)-E(1000 microns), 300 mm2 silicon telescopes Secondary Target – C1H2 – 7.7 mg/cm2
Experimental method: thick secondary target CH2 of 7.7 mg/cm2 Resonances populated in the target. Energy spectrum of 4He, p, d yields excitation function of resonance reaction
8Libeam
E1E2
Si-telescope4He, p
2/
2/,;
)(
)()()(
EE
EE ii
i dEE
EEIEY
ε = stopping power
Energy spectra measured on thick CH2 target at Elab=18.5 MeV
Protons hard to measure, due to low energy (Q=0) and electronic noise
ΔE=50μm
ΔE=20μm
8Li(p,α)5He
0,40 0,60 1,10 1,69 1,76 MeV Resonances in 9Be at Ecm
8Li(p,p)8Li
8Li(p,α)5He
8Li(p,d)7Li
Ecm (MeV)
Contaminant lightparticles subtracted(Au target)
C(8Li,p,d,α) reactionsmeasured, subtracted
Ecm(MeV)
7Li(d,p)8Li
Resonances at 1.66 and 1.76 MeV
decay to 7Li* (0.477MeV), not to 7Ligs,
not populated in 7Ligs(d,p)8Li. Peak shifted to lower energy.
R-matrix analysis of three excitation functions with AZURE
1.66 and 1.76MeV
R-matrix analysis results (Masters Thesis of Erich Leistenschneider 04/2014)
Black numbers Tilley et al Nuc. Phys. A745, 155 (2004)
Blue numbers our analysis
Comparison with previous work
With parameters of the previous work
With parameters of the previous work + width for(p,d) channel
Conclusions
• Elastic scattering measurements with 6He beam on light (9Be, 27Al), medium (51V,58Ni) and heavy (120Sn) targets.
• Optical model and CDCC analysis: for medium and heavy targets, long range absorption, coupling to Coulomb+ nuclear breakup.
• Light targets: 27Al, normal OM. 9Be, CDCC fits the data with coupling to continuum.
• Total reaction cross sections: strong enhancement with halo
projectiles on medium and heavy targets. Coulomb coupling . No enhancement on 27Al. Slight enhancement on 9Be and 12C targets. Nuclear coupling
• The simultaneous measurement of resonant elastic scattering 8Li(p,p)8Li, 8Li(p,α)5He and 8Li(p,d)7Li reactions, allows to determine the resonance parameters of 9Be.
Thank you
Alinka Lépine-Szily (USP)
and RIBRAS collaboration, as: USP: Rubens Lichtenthaler, Kelly C.C. Pires, Erich
Leistenschneider, Valdir Guimarães, Valdir Scarduelli U. Sevilla M. Rodriguez-Gallardo and A. M. Moro ULB (Belgium) Pierre Descouvemont UFF (Niteroi) Djalma R. Mendes Jr, Pedro Neto de Faria, Paulo
R.S. Gomes UNIFEI Viviane Morcelle UFBa Adriana Barioni GSI Juan Carlos Zamora TANDAR (Argentina) Andres Arazi USC Elisangela A. Benjamim