Alpha Stucture of 12B Studied by Elastic Scattering of 8Li Excyt Beam on 4He Thick Target

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Alpha Stucture of 12B Studied by Elastic
Scattering of 8Li Excyt Beam on 4He Thick Target

• M.G. Pellegriti

Laboratori Nazionali del Sud INFN Dipartimento
di Fisica ed Astronomia, Università di Catania
10th International Spring Seminar on Nuclear
Physics Vietri sul Mare, 21-25 May 2010
2
Outlook

• Search for 8Lia cluster state in 12B
• 1) 12B states experiment and theory
• 2) Experimental method 8Lia?12B?8Lia
• ?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

3
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
a 7Li structure
spherical structure, single particle
prolate di-nuclear structure
Y. Kanada-Enyo and H. Horiuchi PRC 52 (1995) 647
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12B states
Investigation of the 8Li-alpha system allows the
observation of 12B states above the decay
threshold
GCM prediction of 8Li-alpha structures indicates
the presence of two rotational bands of opposite
parity
10 MeV
8Li a
P. Descouvemont, NPA 596 (1996) 285
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Thick Target Inverse Kinematic (TTIK) Resonant
Elastic Scattering
Pictorial view
K. P. Artemov et al. Sov. J. Nucl. Phys. 52,
408(1990)
target
E-DE

• inverse kinematics ? forward focused recoil
  alphas
• beam energy loss in the target ? wide range for
  Ecm
• alpha spectra ? information on the resonance
  parameter
• by using R-matrix
  analysis

Ebeam-DEb1
qlab
Ebeam
Ebeam-DEb2
qlab
Ea2-DEa1
Ea1-DEa1
ds/dW
Interference effects are reflected in the
spectrum shape
Ecm
Ecm2
Ecm1
IMPORTANT INGREDIENTS energy loss for beam and
recoil in the target
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Time measurement for the discrimination of
elastic from inelastic events for infinite thick
target
target
E-DE
Ebeam-DE1
a?
qlab
Ebeam-DE2
Ebeam
inelastic
a
qlab
elastic
8Lia
Ea-DEa
same energy
Ea?-DEa?
Problem Ea-DEaEa?-DEa? !!!!
12B
inelastic
elastic
time
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Experimental Set-up
1
5 104pps
2
EXCYT
3
4
qlab0
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Preliminary Results qlab0 telescope
DE(MeV)
a
t
p
Time (ns)
E(MeV)
inelastic as 3.21 MeV, 3 2.25 MeV, 1 0.98 MeV,
2
tritons
DE detector Thickness47mm Resolution 150
keV Time resolution lt1 ns
elastic as simulation
punch-through
DE(MeV)
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Elastic cross section for Ecmlt5MeV
preliminary
ds/dW(mb/sr)
Ecm(MeV)
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Conclusions

• 8Li4He?8Lia has been studied from E30.6 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 (qlab0)
• Evidence for large resonances in the elastic
  scattering spectra has been observed for Ecmlt5MeV
• FUTURE ANALYSIS
• Montecarlo Simulation including
• ?beam profile (experimental collimation)
• ?energy and angular straggling for beam and
  recoil particles
• Error bars estimation
• Data analysis with Ecmgt5MeV (zone with DE-E
  identification)

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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 lIngegneria, Università di Catania, Catania,
  Italy
• f) CSFNSM, Catania, Italy
• g) Ruder Boskovic Institute, Zagreb, Croatia

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Time measurement
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Microchannel Plate
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EXCYT
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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.

are related to
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8Li
12B
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