Physics Division Seminars bring us speakers on a variety of physics related subjects. Usually these are held in the Building 6008 large Conference Room, at 3:00 pm on the chosen day, but times and locations may vary. For more information, contact our seminar chairman,
Tel (Office): (865) 574-6124 (FAX): (865) 574-1268
The facility EXOTIC for the in-flight production of light weakly-bound Radioactive Ion Beams (RIB's) is now fully operational at the Laboratori Nazionali di Legnaro (LNL, Italy). The production technique employs inverse kinematics two-body reactions induced by heavy-ion beams impinging on light gas targets, such as H2, D2, 3He or 4He. Secondary beams of 7Be, 8B and 17F in the energy range 3-5 MeV/u were delivered with intensities of about 250, 1 and 100 kHz, respectively. The Italian Minister of Education, University and Research has recently founded an upgrade of the facility, which will be able to provide in the near future more energetic RIB's.
The 17F secondary beam was used to study the reaction dynamics on 58Ni and 208Pb targets in the energy range around the Coulomb barrier. In particular the scattering process for the system 17F + 58Ni was measured at two colliding energies 20% and 30% higher than the nominal Coulomb barrier. The results were analyzed within the formalism of the coupled-channel code FRESCO to extract the reaction cross section and to investigate the role played by inelastic excitations, transfer channels and by the breakup process 17F to 16O + p. The comparison with the benchmark reaction 16O + 58Ni showed only a rather moderate enhancement (especially when compared to reactions induced by other weakly-bound projectiles, such as 6He, 11Be and 8B, on medium-mass targets) of the reaction cross section at the lower secondary beam energy and pointed out the larger relevance of direct channels, especially of the p-stripping process 17F + 58Ni to 16O + 59Cu.
More recently, in the framework of the commissioning of the new detector array EXPADES the scattering process for the system 17O + 58Ni has been measured in the energy range 42.5-55 MeV in 2.5-MeV steps. 17O is the mirror nucleus of 17F and the two projectiles have very similar nuclear shell-model structures but with very different binding energies: Sn = 4.143 MeV for 17O and Sp = 0.600 MeV for 17F. The reaction cross sections for the two systems, once scaled for the different Coulomb barrier, turned out to be very similar indicating that, in spite of the low projectile binding energy, the breakup process 17F to 16O + p plays a minor role in the reaction dynamics at Coulomb barrier energies.
Finally, the interaction of the 7Be secondary beam with a 58Ni target was investigated at two energies around the Coulomb barrier. The data analysis is at an initial stage.