Alpha Stucture of 12 B Studied by Elastic Scattering of 8 Li Excyt Beam on 4 He Thick Target M.G. Pellegriti Laboratori Nazionali del Sud – INFN Dipartimento di Fisica ed Astronomia, Università di Catania 10 th International Spring Seminar on Nuclear Physics Vietri sul Mare, May 2010

Outlook Search for 8 Li+  cluster state in 12 B 1) 12 B states: experiment and theory 2) Experimental method: 8 Li+   12 B*  8 Li+   Inverse Kinematic Resonant Elastic Scattering on Thick Target  Inverse Kinematic Resonant Elastic Scattering on Thick Target  Problems: superposition of elastic and inelastic scattering  Problems: superposition of elastic and inelastic scattering  Time measurement  Time measurement 3) The Set-up at LNS: 8 Li beam from EXCYT, CT2000 chamber filled with 4 He 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 – 7 Li structure spherical structure, single particle prolate di-nuclear structure Y. Kanada-En’yo and H. Horiuchi PRC 52 (1995) 647

12 B states 12 B states Investigation of the 8 Li-alpha system allows the observation of 12 B states above the decay threshold GCM prediction of 8 Li-alpha structures indicates the presence of two rotational bands of opposite parity P. Descouvemont, NPA 596 (1996) Li + α 10 MeV 8 Li+   12 B*  8 Li+ 

Thick Target Inverse Kinematic (TTIK) Resonant Elastic Scattering E beam -  E b1 E beam -  E b2 E beam target  lab E  -  E  1  lab E    E cm2 E cm1 d  /d  E cm inverse kinematics inverse kinematics  forward focused recoil alphas beam energy loss in the target beam energy loss in the target  wide range for E cm alpha spectra alpha spectra  information on the resonance parameter by using R-matrix analysis Interference effects are reflected in the spectrum shape K. P. Artemov et al. Sov. J. Nucl. Phys. 52, 408(1990) IMPORTANT INGREDIENTS: energy loss for beam and recoil in the target Pictorial view E-  E 8 Li+   12 B*  8 Li+ 

E beam -  E 1 E beam -  E 2 E beam  lab E-EE-E E  inelastic elastic Problem: E  -  E  =E  -  E  !!!! inelasticelastic 8 Li+  12 B   Time measurement for the discrimination of elastic from inelastic events for infinite thick target target E-  E start stop time E  t is important ! inelastic elastic same energy

Experimental Set-up 5 ·10 4 pps EXCYT  lab =0°

Preliminary Results  lab =0° telescope Time (ns)  E(MeV) elastic  ’s simulation inelastic  ’s 3.21 MeV, MeV, MeV, 2 + punch-through tritons  E(MeV)  E(MeV)  t p  E detector Thickness:47  m Resolution: 150 keV Time resolution <1 ns

Elastic cross section for E cm <5MeV d  /d  (mb/sr) E cm (MeV) preliminary

Conclusions 8 Li+ 4 He  8 Li+  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 8 Li-alpha elastic scattering cross section has been obtained around  cm = 180° (  lab =0°) Evidence for large resonances in the elastic scattering spectra has been observed for E cm <5MeV FUTURE ANALYSIS: FUTURE ANALYSIS: Montecarlo Simulation including:  beam profile (experimental collimation)  beam profile (experimental collimation)  energy and angular straggling for beam and recoil particles  energy and angular straggling for beam and recoil particles Error bars estimation Data analysis with E cm >5MeV (zone with  E-E identification) R-matrix analysis to obtain the resonance parameters

Collaboration M.G. Pellegriti a,b, D.Torresi a,b, L. Cosentino a, A. Di Pietro a, C. Ducoin c, M. Lattuada a,b, M.G. Pellegriti a,b, D.Torresi a,b, L. Cosentino a, A. Di Pietro a, C. Ducoin c, M. Lattuada a,b, T. Lonnroth d, P. Figuera a, M. Fisichella a, C. Maiolino a, A. Musumarra a,e, M. Papa d, T. Lonnroth d, P. Figuera a, M. Fisichella a, C. Maiolino a, A. Musumarra a,e, M. Papa d, M. Rovituso b, V. Scuderia,a,f, G. Scalia a,b, D. Santonocito a, M. Zadro g M. Rovituso b, V. Scuderia,a,f, G. Scalia a,b, D. Santonocito a, M. Zadro g 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) The R-matrix R(E) The differential cross section The collision matrix U l The phase shift  l Pole parameters (calculated or formal) Resonance parameters (observed or experimental) With the R-matrix for poles defined as: are related to

8 Li 12 B