1. γ spectroscopy of neutron-rich 95,96 Rb nuclei by the incomplete fusion reaction of 94 Kr on 7 Li Simone Bottoni University of Milan Mini Workshop 1°- year PhD students – October, 15 2012

2. Outline Outline Simone Bottoni - University of Milan o Introduction Why neutron-rich nuclei? Why radioactive beams? Why incomplete fusion reactions? o The experiment 94 Kr + 7 Li @ ISOLDE – CERN (8 th Nov. – 12 th Nov. 2012) Motivation Nuclear structure studies Nuclear reaction studies The experimental setup o Conclusions

3. Introduction – Why neutron-rich nuclei? Simone Bottoni - University of Milan Proton drip line S p = 0 r - process Proton number Neutron number 95,96 Rb Nuclear properties far from stability o Masses and radii o e.m. moments o Level scheme o Spectroscopic factor o Shape transitions o Shape coexistence o Collective excitations o Pairing interaction o Pigmy resonance o Neutron skin o N-N interaction o ……. Few experimental data available! Chart of Nuclides Neutron drip line S p = 0 Nuclear properties well known nearby the valley of stability

4. Introduction – Why radioactive beams? Simone Bottoni - University of Milan Radioactive beams ISOL - Isotope Separation On Line o Accelerated unstable nuclei o Advantages: Discovery and study of new radioactive isotopes Production of very neutron-rich nuclei o Limitations: Intensity ( ≈ 10 5 pps) o IN FLIGHT: Primary heavy ion beam (hundreds MeV/A) Thin target τ < 1 μs No post acceleration High intensity beam o ISOL: Primary protons beam ( 1-1.5 GeV) Thick target τ > 100 ms Post acceleration High purity beam ISOLDE – CERN – 94 Kr - τ = 306 ms - E = 270 MeV - I = 2  10 5 pps

5. Introduction – Why incomplete fusion reactions? Simone Bottoni - University of Milan Elastic break-up Incomplete fusion Complete fusion and cluster evaporation Fusion evaporation reactions Break-up reactions Direct reactions o Complete fusion of projectile and target o Rapid neutrons evaporation o High energy and angular momentum transferred ✓ o Quick decay toward the valley of stability ✗ o Interaction mostly on the surface o Little energy or few particles transferred o Moderately neutron rich-nuclei ✓ o Low energy and angular momentum excited states ✗ o Weakly bound nuclei o High positive Q-Value o Medium -high excited states o Medium-high angular momentum transferred o Moderately neutron-rich nuclei o Supposed to be widely used in future with a new generation of radioactive beams 7 Li ( 94 Kr,αxn)

6. The experiment – Motivation Simone Bottoni - University of Milan 7 Li ( 94 Kr,αxn)  95,96 Rb at ≈ 3 MeV/A Motivation o Nuclear Structure: γ spectroscopy of Rb isotopes at moderate high spin and excitation energy Shape transitions and shell structure in the mass region A ≈ 100 β decay half-life and neutron emission probabilities different in spherical and deformed nuclei o Nuclear reaction: Study of reaction mechanisms and dynamics for incomplete fusion reactions in inverse kinematics Technique o Break-up of 7 Li o Transfer of 3 H in 94 Kr  97 Rb o Evaporation of 1-2 neutrons o Detection of α particles in coincidence with the γ decay r-process 93-99 Rb

7. The experiment – Nuclear structure studies Simone Bottoni - University of Milan Gamma spectroscopyShape transition o Limited Yrast spectroscopy o 7 Li ( 94 Kr,αxn) : Intermediate Energy (up to 14.5 MeV) Intermediate Spin (up to 15 ) G. Georgiev et al. - to be published Coulomb Excitation at ISOLDE - G. Georgiev et al. - to be published J.L.Durell Proc.Int.Conf. On Spectroscopy of Heavy Nuclei, 1990 N. Marginean et al., PRC80(2009), 021301 o Shell structure o N-N interaction o Isomerism o Particle – Vibration coupling

8. The experiment – Nuclear reaction studies Simone Bottoni - University of Milan Theoretical predictions Courtesy: Prof. K. Rusek o Advantages of inverse kinematics: Very forward scattering angles γ Doppler correction reduced o 7 Li ( 94 Kr,αxn): o S α = 2.5 MeV o Q = +9.7 MeV o σ ≈ 35-70 mb o Other relevant reaction channels: 7 Li elastic scattering 7 Li break-up 7 Li ( 94 Kr, 95 Kr) 6 Li 7 Li ( 94 Kr,txn)  Sr isotopes Fusion-evaporation  Y isotopes High selectivity on the 7 Li ( 94 Kr,αxnγ ) reaction channel! C.C calculations for α particle emission C.C calculations for α, t, 6 Li and 7 Li

9. The experiment – Experimental setup Simone Bottoni - University of Milan Experimental setup MINIBALL o HpGe array for γ spectroscopy (MINIBALL) o Si detector for particle identification (T-REX) o Particle – γ coincidence measurements Beam o 8 triple clusters of HpGe o 6 segments for each cluster o Efficiency ≈ 7 % o Energy resolution ≈ 0.5 % at 1.3 MeV o Si detectors in barrel configuration o 2 forward and backward CD o 8 barrels (4 in the current configuration) o E – ΔE telescopes o Angular coverage for the current configuration 24° < ϑ < 65° Courtesy: F. Flavigny T-REX

10. Conclusions Conclusions Simone Bottoni - University of Milan Conclusions o Importance of neutron-rich nuclei o Importance of radioactive beams o Study of the reaction 7 Li ( 94 Kr,αxn) at 3 MeV/A o ISOLDE facility and particle – γ measurement o Shape transition and nuclear structure in Rb isotopes o Incomplete fusion reactions in inverse kinematics o Important test for future experiments with incomplete fusion reactions and a new generation of heavier radioactive beams (Sn, Hg) at new facilities of higher energy and intensity (HIE-ISOLDE, SPIRAL2, SPES etc. )

11. Thank you for your attention Simone Bottoni - University of Milan