Low-lying collective excitations in (18)F(g.s.) and (18)F(m) studied via intermediate-energy Coulomb excitation.

The unstable nuclei 18Fg.s. and 18Fm have been studied via intermediate-energy Coulomb excitation in an attempt to populate collective states above the short-lived 18Fm 1.1 MeV (Jpi = 5+) isomeric (t1/2 = 162 ns) state. A radioactive beam of 18F and 18Fm nuclei was produced by nucleon transfer to energies per nucleon (E/A) of 40 MeV/u, delivered to a 197Au target for Coulomb-excitation. Photons emitted in the vicinity of the 197 Au target were detected in a large-angle NaI(Tl) array, which allowed for the identification of the excited states populated by intermediate-energy Coulomb excitation. Upper limits were established for reduced transition probabilities B(E2; 5+ → 4+,3+) of several predicted transitions from the 18Fm isomeric state. The reduced transition strengths, B(Elambda ↑ ), of two 18F ground state excitations were also directly measured via intermediate-energy Coulomb excitation for the first time. The energies and B(Elambda ↑ ; 1+g.s. → 2+2523,2--2101 ) values for these transitions are reported. An indication of enhanced isomer decay, possibly due to the Coulomb interaction with the target is seen and discussed.Ph.D.Nuclear chemistryNuclear physicsPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/132507/2/9963929.pd