Elastic scattering of halo projectiles at low energies
Outline
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Introduction – RIB in the world
The RIBRAS (Radioactive Ion Beams in Brasil) system
Elastic scattering of 6He on 120Sn, 58Ni, 27Al and 9Be targets
Experiments with the double solenoid system
A diffractive model for elastic scattering of exotic nuclei
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
 Introduction – RIB in the world
Nuclides chart in 1965 and in 2011
protons
~1200 known
presently ~ 3500 and 283 stable
protons
neutrons
neutrons
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
 Introduction – RIB in the world
The ends of the nuclear landscape
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CriticalStability-Oct/2014 Santos - São Paulo
Halos and skins
Borromean nuclei (3-body systems)
New magic numbers and quenching of the shell
gaps.
Importance in astrophysics –
overcoming the A=5,8 gap
synthesis of elements heavier than Fe
New shapes and deformations – fundamental
symmetries
Superheavy elements
R. Lichtenthäler
 Introduction – RIB in the world
Light exotic nuclei
unstable proton rich
17Ne
10
9
proton number
2p-halo
8
1
n
1
3H
2
18
20
12C 13C
5 B
1p-halo
7
4 Be
weakly bound 3 6Li 7Li
2 3He 4He
2H
unstable neutron rich
19F
14N
6
1H
22Ne
16O 17O 18O
8
7
8B
20Ne
4
9Be 10Be
8Li
12
proton halo
borromean
11Be
double magic
6He
11Li
1n-halo
2n-halo
CriticalStability-Oct/2014 Santos - São Paulo
14
8
6
neutron number
24O
10
9Li
8He
stable
neutron halo
16
10B 11
B
22
nucleus
S.E(MeV) (structure)
11Li (T =8.75ms)
0.300 (n+n+9Li)
1/2
6He (T =807ms)
0.973 (2n+alfa)
1/2
11Be (T =13.81s)
0.501 (n+10Be)
1/2
8B (T =770 ms)
0.137 (p+7Be)
1/2
R. Lichtenthäler
 Introduction – RIB in the world
stable R=r0*A1/3
Tanihata - 1985
6He
But for Halo nuclei: 11Li,6He, 11Be ...
R > r0 A1/3
11Li

•
•
3-body forces
Efimov states
r
11Li
Radius of nucleus (fm)
R
Lithium isotopes
7Li
6Li
8Li
9Li
Number of neutrons
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
 Introduction – RIB in the world
Production of Radioactive Ion Beams(RIB)
In-flight
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•
•
ISOL
Relatively easy to implement
Intense secondary beams
Not so good beam characteristics:
emitance and contaminations
CriticalStability-Oct/2014 Santos - São Paulo
•
•
•
R. Lichtenthäler
More complex implementation
Requires a post accelerator
Good quality secondary beams
 RIB in the world
Dubna
Lanzhou
Present intensities ~ 105 to 107 pps
future: RIKEN (japão), SPIRAL2 (França), FAIR (GSI),
FRIB(EUA) intensities will be of ~ 109 – 1012 pps !!
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
•
The RIBRAS system
The São Paulo Pelletron Laboratory
primary Li,Be,B,C,O,Si,Cl
I~500nAe-mAe
8 UD
CriticalStability-Oct/2014 Santos - São Paulo
2-5 MeV/A
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RIBRAS – since 2004
•
The RIBRAS system
scattering chamber
mid scattering chamber
primary beam
primary target
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
•
The RIBRAS system
First solenoid
angular acceptance
2 deg<Dq <6 deg
DW=30 msr
Bρ =
mv
q
=
2 mE
q
primary beam
1- primary target
2- collimator
3- Faraday cup
4- solenoid
CriticalStability-Oct/2014 Santos - São Paulo
5- lollipop
6-collimator
7- scattering chamber,secondary target
and detectors
R. Lichtenthäler
•
The RIBRAS system
Secondary Beam
Production Reaction
6He
9Be(7Li,6He)
8Li
9Be(7Li,8Li)
7Be
3He(6Li,7Be)
7Be
3He(7Li,7Be)
8B
3He(6Li,8B)
10Be
9Be(11B,10Be)
7Be
7Li(6Li,7Be)
Intensity (pps)
Iprimary ~ 300 nAe
Neutron halo
Borromean
proton halo
10+5
10+5
10+5
10+5
10+4
10+4
105
Energy of the secondary beams 10-30 MeV
depending on the beam.
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
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The RIBRAS system – identification spectra
9Be(7Li,8Li)8Be
cocktail beam
DE
particle
DE
20mm
150 mm²
Detector at zero deg.
no secondary target
7Li
E
1000 mm
8
Li (0.98;1+) 8Li gs
8Li
lollipop
gs
DE-E telescope
7Li2+
8Li*
FWHM=470 keV
8Li3+
6He2+
p,d,t
CriticalStability-Oct/2014 Santos - São Paulo
4He2+
alphas
R. Lichtenthäler
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The RIBRAS system – identification spectra
6He+120Sn
6He+9Be
p,d,t
t
6He+197Au
6He+58Ni
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
•
Elastic scattering of 6He on several targets
Calculations
• Optical Model
• 3 and 4 body CDCC
4He+51V
6He+51V
6He+9Be
6He+27Al
CriticalStability-Oct/2014 Santos - São Paulo
6He+120Sn
R. Lichtenthäler
around the Coulomb barrier: E~Eb
q1/4
lg
Fresnel diffraction type (Coulomb-nuclear interference)
Coulomb+nuclear
V
Coulomb barrier
E
above the Coulomb barrier: E>>Eb
r
6He+9Be
Fraunhofer diffraction type
Dq=p/lg ; lg=kR
Far side
Near side
nuclear
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
•
Elastic scattering of 6He on several targets
4 body CDCC calculations
diPietro et al.
6He+120Sn
predictions!
Y.Y. Yang et al.
8B+208Pb
6He+208Pb
@ 27 MeV
CriticalStability-Oct/2014 Santos - São Paulo
q1/4
lg
R. Lichtenthäler
9,10,11Be+64Zn
•
Elastic scattering of 6He on several targets
4-body effects, V. Morcelle et al., PLB 732, 228 (2014)
j=7
6He+58Ni
[Ti+Uii-Ei]Yi=UijYj
j=6
j=5
j=4
j=3
Bin
contiuum
j=2
i=1
gs
U6He-T = <f6He|Ua-T+Un-T+Un-T|f6He>
no free parameters
4-body- M. Rodríguez-Gallardo
T
R
6He
3 body (Eb=0.973 MeV) and modified
3-body (Eb=1.6 MeV) -K.C.C. Pires and A.M Moro
T
R
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
6He
•
Elastic scattering of 6He on several targets
K.C.C. Pires et al. PRC (2014)
6He+9Be
T
R
6He
U6He-T = <f6He|Ua-9Be+U2n-9Be|f6He>
V
R
r
where Ua-9Be is known empirically and
U2n-9Be is adjusted to fit the data
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
•
Elastic scattering of 6He on several targets
Reduced
reaction
cross section
6He+
120Sn
exotic
Reaction cross-section obtained from
the elastic scattering (CDCC,OM,CC)
s

red
tightly bound
s
reac
1
/3
shalo=s6He+120Sn-s4He+120Sn
1
/3 2
(A
A
p 
t )
E
/3
1
/3
cm 1
E

(
A

A
red
p
t )
Z
Z
p
t
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
•
Elastic scattering of 6He on several targets
Reduced cross-sections for intermediate mass systems A~60
exotic
6He+58Ni
6He+51V
6He+64Zn
weakly bound
8B+58Ni
6Li+51V
9Be+64Zn
tightly bound
6Li+58Ni
6Li+64Zn
7Be+58Ni
4He+58Ni
4He+51V
16O+64Zn
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
•
Elastic scattering of 6He on several targets
Reduced cross section for light systems (9Be target).
enhancement
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
•
Elastic scattering of 6He on several targets
Percent enhancement for several systems
[this work]
[this work]
[this work]
guideline
Ds 
CriticalStability-Oct/2014 Santos - São Paulo
s
reac
(exp) - s
s
psp
psp
6
( Li )
6
( Li )
R. Lichtenthäler
•
Experiments with the double solenoid system
scattering chamber
mid scattering chamber
primary beam
primary target
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
•
Experiments with the double solenoid system
Crossover mode
Solenoid 1
Solenoid 2
Primary
beam
lollipop
colimator
Faraday cup
lollipop
1 meter
Primary target
Secondary
target
parallel mode
Solenoid 1
Solenoid 2
Rad. shield
g detector
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
•
6Hesolenoid
Experiments with the double
system
Beam purity
1 solenoid
6He
double solenoid
6He
beam 92% purity
beam 16%
Solenoid 1
Solenoid 2
absorber
Primary beam
lollipop
Faraday cup
Primary target
CriticalStability-Oct/2014 Santos - São Paulo
Colimator
Beam
blocker
(lollipop)
R. Lichtenthäler
•
Experiments with the double solenoid system
1 solenoid
8Li
double solenoid
Beam purity
Solenoid 1
Solenoid 2
absorber
Primary beam
lollipop
Faraday cup
Primary target
CriticalStability-Oct/2014 Santos - São Paulo
Colimator
Beam
blocker
(lollipop)
R. Lichtenthäler
•
Experiments with the double solenoid system
Excitation function measurements. Experiments with the thick target method
-resonances in 6He+p=7Li and 8Li+p=9Be.
CH2 12 mg/cm2
protons
6He
E6He=12.2 MeV
E cm  E lab
M
M
p

T
M
T
1
7
Silicon telescope
DE E
spectrum of light particles
range
E lab
resonances in the CN
50mm
1000mm
11.7
11.2
Ecm+Q
7He
10.8
p+6He ; 9.975 MeV
7Li
GS ; 0 MeV ; 3/2-
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
p(6He,p)6He
CriticalStability-Oct/2014 Santos - São Paulo
p(6He,p)6He excitation functions
R. Lichtenthäler
The p(8Li,p)8Li scattering
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
Three excitation functions with R-matrix calculations (AZURE)
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
•
A diffractive model for elastic scattering
Ericson parameterization of the S-matrix (1960’s)
|Sl|
1
Sl 
1  exp(
Lg - l
D
1
- ia )
D
0.5
bimpact parameter
Lg
3 parameters only; Lg=kLR ; R=r0(Ap1/3+At1/3) ; k L  2 m ( E - V B ) / 
D=kLa ; a =0.65 fm for stable nuclei  diffuseness
a  phase (-p/2<a<p/2)
f N (q ) 
1
2 ik
 ( 2 l  1)( S l - 1) e
2 is l
Pl (cos q )
f (q )  f N (q )  f Coul (q )
ds
dW
 || f (q ) ||
2
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
l=kb
•
A diffractive model for elastic scattering
Results for 6He and 11Li+208Pb and 6He+9Be
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
•
A diffractive model for elastic scattering
L grazing – 6He+208Pb
Delta - 6He+208Pb
D=ka with a=0.65 fm
for the 6He and 11Li+208Pb systems  D>>ka
due to long range effects: Coulomb x nuclear breakup
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
A diffractive model for elastic scattering
Fresnel peak due to Coulomb – nuclear interference effects
A. Diaz-Torrez, PLB (2014)
f (q )  f N (q )  f Coul (q )
ds
dW

d s Coul
dW

ds
N
dW
 2 | f Coul || f N | cos f
cos(f) between nuclear and Coulomb amplitudes
cos(f)
•
delta=0.658
delta=4.128
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
Summary
 A systematic enhancement was observed in the total
reaction cross section of systems with 6He projectiles, with
respect to other stable weakly bound projetiles on the
several targets.
 This enhancement dependends on the mass of the target,
being larger for heavier targets.
 Experiments using the thick target method are in progress.
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler
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 Bruxelles
P. Descouvemont
Laboratorio Tandar, Buenos Aires, Argentina
A. 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, EUA
J. Kolata
Faculty of Science, The M.S. University of Baroda, India
Surjit Mukherjee
CriticalStability-Oct/2014 Santos - São Paulo
R. Lichtenthäler