elastic scattering of halo projectiles at low energies

CriticalStability-Oct/2014 - CriticalStability-Oct/2014 - Santos - São Paulo Santos - São Paulo

R. LichtenthälerR. Lichtenthäler

Elastic scattering of halo projectiles at low energiesElastic scattering of halo projectiles at low energies

OutlineOutline Introduction – RIB in the worldIntroduction – RIB in the world The RIBRAS (Radioactive Ion Beams in Brasil) systemThe RIBRAS (Radioactive Ion Beams in Brasil) system Elastic scattering of Elastic scattering of 66He on He on 120120Sn, Sn, 5858Ni, Ni, 2727Al and Al and 99Be targetsBe targets Experiments with the double solenoid systemExperiments with the double solenoid system A diffractive model for elastic scattering of exotic nucleiA diffractive model for elastic scattering of exotic nuclei



presently ~ 3500 and 283 stable

~1200 known

Nuclides chart in 1965 and in 2011

neutrons

pro

ton

s

pro

ton

s

neutrons

Introduction – RIB in the worldIntroduction – RIB in the world



The ends of the nuclear landscapeThe ends of the nuclear landscape

• Halos and skinsHalos and skins• Borromean nuclei (3-body systems)Borromean nuclei (3-body systems)• New magic numbers and quenching of the shell New magic numbers and quenching of the shell

gaps. gaps.• Importance in astrophysics – Importance in astrophysics –

overcoming the A=5,8 gapovercoming the A=5,8 gap

synthesis of elements heavier than Fe synthesis of elements heavier than Fe • New shapes and deformations – fundamental New shapes and deformations – fundamental

symmetriessymmetries• Superheavy elementsSuperheavy elements




12

3

41

2

4

5

6

78

6

8

9

1012 14

16

neutron number

pro

ton

nu

mb

er

18 20 22

10

stable

neutron halo

proton halo

borromean

11Li6He

8B

Light exotic nuclei

24O

unstable neutron rich

11Be

2n-halo

1n-halo

1p-halo

1H 2H 3H

3He 4He 8He

6Li 7Li 8Li 9Li

unstable proton rich

9Be 10Be7Be

11B10B

n

12C 13C

14N

16O 17O 18O

20Ne

19F

22Ne17Ne

2p-halo

nucleus S.E(MeV) (structure)11Li (T1/2=8.75ms) 0.300 (n+n+9Li) 6He (T1/2=807ms) 0.973 (2n+alfa)11Be (T1/2=13.81s) 0.501 (n+10Be) 8B (T1/2=770 ms) 0.137 (p+7Be)


double magic

weakly bound

8B



R > r0 A1/3

r

R

But for Halo nuclei: 11Li,6He, 11Be ...

Number of neutrons

6Li

7Li8Li

9Li

11Li

Rad

ius

of

nu

cle

us

(fm

)

Lithium isotopes

11Li

6He

Tanihata - 1985

stable R=r0*A1/3


• 3-body forces

• Efimov states



Production of Radioactive Ion Beams(RIB)Production of Radioactive Ion Beams(RIB)

• Relatively easy to implement

• Intense secondary beams

• Not so good beam characteristics:

emitance and contaminations

• More complex implementation

• Requires a post accelerator

• Good quality secondary beams

In-flight ISOL




Dubna

Lanzhou

Present intensities ~ 105 to 107 pps

future: RIKEN (japão), SPIRAL2 (França), FAIR (GSI), FRIB(EUA) intensities will be of ~ 109 – 1012 pps !!

RIB in the worldRIB in the world



8 UD RIBRAS – since 20042-5 MeV/A

The São Paulo Pelletron LaboratoryThe São Paulo Pelletron Laboratory

primary Li,Be,B,C,O,Si,Cl

I~500nAe-Ae

• The RIBRAS systemThe RIBRAS system



mid scattering chamberscattering chamber

primary beam

primary target




First solenoidFirst solenoid

q

mE=

q

mv=Bρ

2

1- primary target2- collimator3- Faraday cup4- solenoid

5- lollipop6-collimator7- scattering chamber,secondary target and detectors

angular acceptance

2 deg<<6 deg

primary beam

=30 msr




Secondary Beam Production Reaction

Intensity (pps) Iprimary ~ 300 nAe

6He 9Be(7Li,6He) 10+5

8Li 9Be(7Li,8Li) 10+5 7Be 3He(6Li,7Be) 10+5 7Be 3He(7Li,7Be) 10+5 8B 3He(6Li,8B) 10+4

10Be 9Be(11B,10Be) 10+4 7Be 7Li(6Li,7Be) 105

Energy of the secondary beams 10-30 MeV

depending on the beam.

Neutron halo

Borromean

proton halo




FWHM=470 keV

Detector at zero deg.no secondary target

8Li*

8Ligs

7Li2+

4He2+

6He2+

99Be(Be(77Li,Li,88Li)Li)88BeBe

alphas

8Li3+

p,d,t

E

lollipopE-E telescope

8Li gs8Li (0.98;1+)7Li

cocktail beam

E E

particle

m 1000 m

150 mm²150 mm²

• The RIBRAS system – identification spectraThe RIBRAS system – identification spectra



66He+He+99BeBe

6He+197Au

6He+120Sn

t

6He+58Ni

p,d,t

• The RIBRAS system – identification spectraThe RIBRAS system – identification spectra



6He+27Al 6He+120Sn

6He+9Be

6He+51V

4He+51V

Calculations

• Optical Model

• 3 and 4 body CDCC

• Elastic scattering of Elastic scattering of 66He on several targetsHe on several targets



around the Coulomb barrier: E~EbFresnel diffraction type (Coulomb-nuclear interference)

lg

Far side

Near side

Fraunhofer diffraction type

above the Coulomb barrier: E>>Eb

=/lg ; lg=kR

6He+9Be

Coulomb+nuclear

nuclear

r

V

Coulomb barrierE



9,10,11Be+64ZndiPietro et al.4 body CDCC calculations

6He+208Pb

@ 27 MeV

predictions!

lg

Y.Y. Yang et al.

6He+120Sn

8B+208Pb




U6He-= <6He|UT+Un-T+Un-T|6He>

no free parameters

n

nx

y

R

6He

2n

y

R 6He

gsi=1

j=2

j=3

j=4

j=5

j=6

j=7

contiuum

4-body- M. Rodríguez-Gallardo

3 body (Eb=0.973 MeV) and modified

3-body (Eb=1.6 MeV) -K.C.C. Pires and A.M Moro

[Ti+Uii-Ei]i=Uijj

Bin


4-body effects, V. Morcelle et al., PLB 732, 228 (2014)

6He+58Ni



K.C.C. Pires et al. PRC (2014)

U6He-= <6He|U9Be+U2n-9Be|6He>

where U-9Be is known empirically and

U2n-Be is adjusted to fit the data

2n

y

R

6He

r

V

R


6He+9Be



tightly bound

weakly boundexotic

halo=6He+120Sn-4He+120Sn

6He+120Sn

)( 3/13/1tp

tp

cmred AA

ZZ

EE


23/13/1 )( tp

reacred

AA

Reduced reaction cross section

Reaction cross-section obtained from

the elastic scattering (CDCC,OM,CC)



Reduced cross-sections for intermediate mass systems A~60

6He+58Ni

6He+51V

6He+64Zn

8B+58Ni

6Li+51V

9Be+64Zn

6Li+58Ni

6Li+64Zn

7Be+58Ni

4He+58Ni

4He+51V

16O+64Zn

tightly bound

weakly bound

exotic




Reduced cross section for light systems (9Be target).

enhancement




)(

)((exp)6

6

Li

Lipsp

pspreac

guideline

Percent enhancement for several systems

[this work]

[this work]

[this work]




mid scattering chamberscattering chamber

primary beam

primary target

• Experiments with the double solenoid systemExperiments with the double solenoid system



Crossover mode

Solenoid 2Solenoid 1

Rad. shield

detector

parallel modePrimary target

Faraday cup

Solenoid 2

Secondary target

colimator

Solenoid 1

Primary beam

1 meter

lollipop lollipoplollipoplollipop




1 solenoid double solenoid

6He beam 92% purity6He beam 16%


Primary target

Faraday cup

Beam blocker

(lollipop)

Colimator

Primary beam

absorber

66He Beam purityHe Beam purity

lollipop




1 solenoid double solenoid


Primary target

Faraday cup

Beam blocker

(lollipop)

Colimator

Primary beam

absorber

lollipop


88Li Beam purityLi Beam purity



Excitation function measurements. Experiments with the thick target method

-resonances in 6He+p=7Li and 8Li+p=9Be.

6He protons

range

CH2 12 mg/cm2

E6He=12.2 MeVspectrum of light particles

E E

50m1000m

Silicon telescope

7Li

p+6He ; 9.975 MeV

Ecm+Q

GS ; 0 MeV ; 3/2-

10.8

11.7

7He11.2

resonances in the CN

labTp

Tlabcm E

MM

MEE

7

1




p(6He,p)6He p(6He,p)6He excitation functions



The p(8Li,p)8Li scattering



Three excitation functions with R-matrix calculations (AZURE)



Ericson parameterization of the S-matrix (1960’s)

)exp(1

1

ilLg

S l

3 parameters only; Lg=kLR ; R=r0(Ap1/3+At

1/3) ;

=kLa ; a =0.65 fm for stable nuclei diffuseness

phase (-/2<</2)

/)(2 BL VEk

2

2

||)(||

)()()(

)(cos)1)(12(2

1)(

fd

d

fff

PeSlik

f

CoulN

li

lNl

l=kb

|Sl|

1

0.5

Lg

bimpact parameter

• A diffractive model for elastic scattering



Results for 6He and 11Li+208Pb and 6He+9Be




L grazing – 6He+208Pb Delta - 6He+208Pb

for the 6He and 11Li+208Pb systems>>kadue to long range effects: Coulomb x nuclear breakup

=ka with a=0.65 fm




Fresnel peak due to Coulomb – nuclear interference effectsA. Diaz-Torrez, PLB (2014)

cos||||2

)()()(

NCoulNCoul

CoulN

ffd

d

d

d

d

d

fff


cos(betweennuclear and Coulomb amplitudes

cos

) delta=0.658

delta=4.128



SummarySummary

A systematic enhancement was observed in the total A systematic enhancement was observed in the total reaction cross section of systems with reaction cross section of systems with 66He projectiles, with He projectiles, with respect to other stable weakly bound projetiles on the respect to other stable weakly bound projetiles on the several targets.several targets.

This enhancement dependends on the mass of the target, This enhancement dependends on the mass of the target, being larger for heavier targets.being larger for heavier targets.

Experiments using the thick target method are in progress.Experiments using the thick target method are in progress.



RIBRAS collaboration:

Universidade de São Paulo, IFUSP

A. Lépine-Szily, R. Lichtenthäler Fo, V. Guimarães, M.A.G. Alvarez, L. Gasques,P. N.deFaria,D.Mendes, K.C.C. Pires, V.Morcelle, E. A. Benjamim, A. Barioni, M.C. Morais, M. Assunção, R. PampaCondori, E.Leistenschneider, O. Camargo Jr., J. Alcantara-Nunez, V. Scarduelli, D. Pereira, M.S. Hussein

Universidad de Sevilla, Espanha

A.M. Moro, M. Rodríguez-Gallardo

Université Libre de BruxellesP. Descouvemont

Laboratorio Tandar, Buenos Aires, ArgentinaA. Arazi

CEADEN, Havana, Cuba I.Padron Universidade Federal Fluminense (UFF)P.R.S. Gomes, J. Lubian, J.M.B. Shorto, D.S. Monteiro

University of Notre Dame, EUAJ. Kolata

Faculty of Science, The M.S. University of Baroda, IndiaSurjit Mukherjee

elastic scattering of halo projectiles at low energies

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