Recent results on reactions with radioactive beams at RIBRAS

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cent results on reactions with dioactive beams at RIBRAS linka Lépine-Szily, and IBRAS collaboration T* workshop on Low-Energy Reaction namics of Heavy-Ions and Exotic Nuclei y 26-30, 2014, Trento, Italy

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 Presentation

Transcript of Recent results on reactions with radioactive beams at RIBRAS

Page 1: Recent results on reactions with radioactive beams at RIBRAS

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

Page 2: Recent results on reactions with radioactive beams at RIBRAS

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

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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, ...

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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

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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%

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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

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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

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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)

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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.

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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

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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)

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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

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)(4 mbCDCCbreaction

)(mbbreakup

6He+120Sn elastic scattering

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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

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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

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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.

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Production of α-particles

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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

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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

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Total reaction cross sections

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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.

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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:

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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)

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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

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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)

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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

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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)

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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.

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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 ????

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Measurements with purified radioactive beams:

Elastic scattering and transfer reactions on hydrogen target

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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:

Page 32: Recent results on reactions with radioactive beams at RIBRAS

α+5He

2.467 MeV

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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)

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R-matrix fits:•Spins•Energies•Proton and alpha widths

Astrophysical reaction rates

Results of our previous 8Li(p,)5He measurement:

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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.

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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

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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

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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

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ΔE=50μm

ΔE=20μm

8Li(p,α)5He

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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

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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.

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R-matrix analysis of three excitation functions with AZURE

1.66 and 1.76MeV

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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

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Comparison with previous work

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With parameters of the previous work

With parameters of the previous work + width for(p,d) channel

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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.

Page 47: Recent results on reactions with radioactive beams at RIBRAS

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