Evaporation residue formation competing with the fission process in the197Au+16O,12C reactions and fission barriers at a specifiedJ window

Abstract

Evaporation-residue excitation functions for 160 and 12C~-19VAu reactions were measured by means of the activation technique. The competition between evaporation and fission of the compound nuclei was studied by comparing the observed evaporationresidue data with the published fission excitation functions, A newly devised analysis was applied in order to deduce a fission barrier height at a specified angular momentum and determine the relevant fissioning nucleus as well. We found the fission barriers to be 8.2 MeV for the 211Fr nucleus at 16h and 8.2 MeV for the 2~ nucleus at 27h.

Spectroscopy and high-spin structure ofFr209

“…Absolute cross sections for fusion evaporation reactions for 16 O incident on 197 Au are known to be in the region of 100-200 mb [10][11][12] with the dominant residues being the xn products, the francium isotopes. As fission competition becomes more important, the survival probability for cases where charged particles are evaporated is relatively increased, hence radon isotopes from the pxn evaporation channels are also observed.…”

“…There have been several studies involving oxygen beams, which concur with this prediction (see, for example, Refs. [13,14]), and furthermore, the xn differential cross sections have been measured [10]. Although most of the cross-section studies involve measurement of the α activities for the known ground-state α decays, these are complicated by the fact that the α-particle energies for neighboring isotopes such as the pair 210,211 Fr and 208,209 Fr are not resolved within the pair (see, for example, Ref.…”

“…[14]). However, the early study of Baba et al [10] used the additional technique of mass separation to recover individual xn cross sections for 16 O on 197 Au. They report the peak of the 4n channel leading to 209 Fr to be at a center-of-mass energy of ∼82 MeV, corresponding to a beam energy of ∼89 MeV, in good agreement with our predictions and with their own calculations.…”

Assignment of levels in 208Fr and 10- isomers in the odd-odd isotones 206At and 208Fr

“…Note also that our assignment is in fact consistent with pre-existing crossa e-mail: George.Dracoulis@anu.edu.au section measurements for the ( 16 O, xn) reactions (see, for example, refs. [6][7][8][9]). Some information on the still lighter range of isotopes, [205][206][207] Fr, has also recently been reported [10].…”

Investigation of the fusion process for B10+Au197 at near-barrier energies

“…Now we present a comparison of the experimental fusion cross sections for 10 B + 197 Au with data for other systems involving the same target nucleus. These data were obtained in [34][35][36][37][38][39][40], with projectiles ranging from 4 He to 48 Ca. In order to remove trivial differences of the fusion cross sections related to the "size" of the system, we adopt the reduced energy and cross section as proposed in [41,42].…”