Nuclear reactions

LSC-setup.jpgDuring the summer of 2017 we have conducted three major experiments at the Large Scattering Chamber: (i) 5He Cluster Transfer by Scattering of 2H from a Be target, (ii)Study of 11B (3He, d) 12C reaction, and (iii) Study of the ternary decay channel induced by shell effects via the reactions 34S + 208Pb and 37Cl + 205Tl. In addition, we had test measurements in preparation for experiments scheduled for 2018. One the important topics for us is testing the strength of the shell closure at N=82 via multinucleon transfer reactions at energies around the Coulomb barrier. Shell quenching in neutron-rich nuclei is of particular interest for the astrophysical nucleogenesis of the heavy elements as it affects the relative capture and decay rates in the vicinity of the waiting points of the r-process. The structures of the N=82 isotones with Z below the doubly magic nucleus 132Sn are of crucial importance because of their connection with the peak at A≈130 in the solar r-process abundance distribution.

Another important astrophysical problem we are investigating is determination of the strength of the second-forbidden transition between the ground states of 20F and 20Ne. The result is of critical importance to understand the final evolution stages of stars in the mass range between 8 and 10 solar masses. Especially for this experiment we have refurbished our old intermediate-focus spectrometer capable of focusing electrons up to 8 MeV. A new scintillator telescope with a muon veto was designed and constructed. The background tests were made in the Pyhäsalmi mine at the depth of 1.4 km. The final measurement was carried out in January 2018 using 20F beam produced by the IGISOL facility.