Rare isotope physics
- Proton radioactivity of very neutron deficient nuclei lying close to the proton drip-line. The structure and the deformation of drip line nuclei is determined with the aim to fully understand the r-p chain in the stars.
- Exotic (14C, 24Ne, 34Si…) cluster radioactivity from trans-lead nuclei. The half lives of the spontaneous emission of rare isotopes are compared to normal radioactivity: alpha decay and spontaneous fission.
- Nuclear reaction mechanisms. The cross section of reactions such as elastic scattering, Coulomb and nuclear break-up, sub-barrier fusion give evidence to nucleon halo or skin configuration and to the excitation of exotic modes ( exotic giant resonances, low energy dipole strength).
The facilities of the ATLAS, GANIL, Louvain la Neuve and RIKEN laboratories are used for the experiments. Besides the design and construction of advanced items for specific measurements, the experiment has also the aim to assembly a line for the production of secondary exotic beams following inverse kinematics reactions induced on ligth targets by LNL accelerator beams. The first beam will be 17F produced through the reaction p(17O,17F)n.
Structure of the collaboration:
- Milano: A. Guglielmetti, R. Bonetti (local spokesperson).
- Napoli: A. De Rosa, G. Inglima, M. La Commara, D. Pierroutsakou. M. Romoli (local spokesperson), M. Sandoli (national spokesperson).
- Padova: A. Andrighetto, C. Signorini (local and national co-spokesperson), L. Stroe
- Udine: F. Soramel.
The collaboration with research teams of Argonne, CEA-DAPNIA-Saclay, Orsay, Dubna, Moskow, RIKEN is also active.
The recoils produced in a fusion evaporation reaction are analyzed according to their M/q ratio and focused on the focal plane detector (MWPC); interesting recoils go through the MWPC detector and are implanted in a (40x40) 1 mm2 Double Sided Silicon Strip Detector (DSSD) where they decay.
The particle emitted in the decay is also detected by the DSSD and time relation between the two events is given by a 4 MHz clock.
The coincidence between the heavy complex residue, detected in the magnetic spectrometer, and the lights charged fragments, detected by the telescope of Si microstrip detector array allows a complete determination of the event kinematics. To the detection system of the charged products, a multidetector array for particle- gamma-ray coincidence measurement can be associated. On the left hand side of the figure the scheme designed to produce a 17F beam at the LNL is reported.
Recent Results
Spontaneous emission of heavy clusters (14C,24Ne,34Si…) from trans-lead nuclei have been studied with track detectors calibrated at Legnaro tandem. Branching ratios relative to alpha decay as low as 10-16 and half lives as long as 1029 s have been recently obtained. The most recent experiments have been performed on several Uranium isotopes. The cluster decay half lives show strong shell effects, in contrast with spontaneous fission ones.
Proton radioactivity
Two levels in 117La p-decay to 116Ba ground state have been studied: the ground state (Ip = 3/2+)and a metastable state (Ip = 9/2+) at 150 keV excitation energy. The 9/2+ state decaying through a pure M3 g transition would live 44 s (T1/2 Weisskopf estimation), too long to compete with the faster (T1/2 = 10 ms) proton decay. Comparing the experimental data with calculations from Maglione et al. Phys. Rev. C59 (1999) R589, deformations for the two levels are deduced.
The cross sections for elastic scattering of the weakly bound 9Be on 209Bi around the Coulomb barrier have been measured with ~ 5% absolute accuracy from 40 to 48 MeV. The potential obtained from an optical model analysis has an unusual behavior. At the strong absorption radius the imaginary (absorptive) potential is increasing (rather than decreasing) with decreasing energy, as would be consistent with a long range polarization potential arising mainly from couplings to breakup channels. The real part, on the other hand, displays a strong attractive polarization contribution with the maximum at the barrier, as would be normally expected from a polarization contribution arising from strong couplings. The inelastic multiplet in 209Bi of collective nature around 2.6 MeV, originating from the coupling [ 208Pb(3- )
h9/2- ]Jp , was seen only at 48 MeV. The total multiplet cross section is well reproduced by coupled channel calculations with the potential obtained from the optical analysis and the experimental B(E3) strengths of the 209Bi multiplet levels.
