M.G. Pellegriti
Laboratori Nazionali del Sud – INFN
Dipartimento di Fisica ed Astronomia, Università di Catania
Alpha Stucture of 12B Studied by
Elastic Scattering of 8Li Excyt Beam
on 4He Thick Target
10th International Spring Seminar on Nuclear Physics
Vietri sul Mare, 21-25 May 2010
Outlook
Search for 8Li+a cluster state in 12B
1) 12B states: experiment and theory
2) Experimental method: 8Li+a12B*8Li+a
Inverse Kinematic Resonant Elastic Scattering on Thick Target
Problems: superposition of elastic and inelastic scattering
Time measurement
3) The Set-up at LNS: 8Li beam from EXCYT, CT2000 chamber filled with 4He gas
4) Preliminary results
5) Conclusions
Exotic Clustering
Clustering in neutron rich nuclei: description of unstable nuclei as di-nuclear structures
Matter density distribution in Boron isotopes ground states (AMD calculations):
drastic changes in the isotopes structure with the increasing number of neutrons
α – 7Li structure
spherical structure, single particle
prolate di-nuclear structure
Y. Kanada-En’yo and H. Horiuchi PRC 52 (1995) 647
12B
states
Investigation of the 8Li-alpha system allows the observation of 12B states above the decay threshold
10 MeV
8Li
GCM prediction of 8Li-alpha
structures indicates the presence of
two rotational bands of opposite
parity
+α
P. Descouvemont, NPA 596 (1996) 285
8Li+a12B*8Li+a
Thick Target Inverse Kinematic (TTIK)
Resonant Elastic Scattering
8Li+a12B*8Li+a
Pictorial view
E-DE
K. P. Artemov et al.
Sov. J. Nucl. Phys. 52, 408(1990)
target
inverse kinematics  forward focused recoil alphas
Ebeam-DEb1
Ebeam-DEb2
qlab
qlab
Ebeam
Ea2-DEa1
beam energy loss in the target  wide range for Ecm
alpha spectra  information on the resonance parameter
by using R-matrix analysis
Ea1-DEa1
ds/dW
Interference effects are reflected in the spectrum shape
Ecm2
Ecm1
Ecm
IMPORTANT INGREDIENTS:
energy loss for beam and recoil in the target
Time measurement for the discrimination of
elastic from inelastic events for infinite thick target
E-DE
target
Ebeam-DE1
a
a
qlab
8Li+a
same
energy
time
Ebeam-DE2
qlab
inelastic
Ebeam
elastic
Ea-DEa
Ea-DEa
Problem: Ea-DEa=Ea-DEa !!!!
12B
elastic
inelastic
inelastic
elastic
Dt is important !
start
E
time
stop
Experimental
Set-up
T=300 °K
P= 700 mbar
4He
Eb=30.6MeV 5 ·104pps
EXCYT
gas
1
a
Kapton foil
8Li
2
3
MCP foil
Si DE-E’s
qlab=0°
a
beam direction
DE3
E3
4
DE(MeV)
Preliminary Results
qlab=0° telescope
a
Time (ns)
t
p
E(MeV)
inelastic a’s
3.21 MeV, 3+
2.25 MeV, 1+
0.98 MeV, 2+
tritons
elastic a’s simulation
punch-through
DE detector
Thickness:47mm
Resolution: 150 keV
Time resolution <1 ns
DE(MeV)
ds/dW(mb/sr)
Elastic cross section for Ecm<5MeV
Ecm(MeV)
Conclusions
8Li+4He8Li+a
has been studied from E=30.6 MeV down to zero
The TTIK experimental technique with the time measurement improvement
allows discrimination between elastic and inelastic (or other) scattering
8Li-alpha
elastic scattering cross section has been obtained around qcm= 180° (qlab=0°)
Evidence for large resonances in the elastic scattering spectra has been observed for Ecm<5MeV
FUTURE ANALYSIS:
Montecarlo Simulation including:
beam profile (experimental collimation)
energy and angular straggling for beam and recoil particles
Error bars estimation
Data analysis with Ecm>5MeV (zone with DE-E identification)
R-matrix analysis to obtain the resonance parameters
Collaboration
M.G. Pellegritia,b, D.Torresia,b, L. Cosentinoa, A. Di Pietroa, C. Ducoinc, M. Lattuadaa,b,
T. Lonnrothd, P. Figueraa, M. Fisichellaa, C. Maiolinoa, A. Musumarraa,e, M. Papad,
M. Rovitusob, V. Scuderia,a,f, G. Scaliaa,b, D. Santonocitoa, M. Zadrog
a) INFN Laboratori Nazionali del Sud, Catania, Italy
b) Dipartimento di Fisica ed Astronomia, Università di Catania, Catania, Italy
c) INFN, Sezione di Catania, Italy
d) Åbo Academy, Turku, Finland
e) Dipartimento di Metodologie Fisiche e Chimiche per l’Ingegneria, Università di Catania, Catania, Italy
f) CSFNSM, Catania, Italy
g) Ruđer Boskovic Institute, Zagreb, Croatia

Time measurement
Microchannel Plate
EXCYT
How to extract the resonance parameters
from the experimental data:
The R-matrix formalism
A.N. Lane and R.G. Thomas, Rev. Mod. Phys. 30 (1958) 257-353.
The R-matrix R(E)
The differential
cross section
The collision matrix Ul
The phase shift dl
With the R-matrix for l poles defined as:
Pole parameters
(calculated or formal)
Resonance parameters
(observed or experimental)
are related to
8Li
12B