Fusion and quasi-fission in the formation of heavy elements

Abstract

Abstract. The time scales of the dynamical nuclear rearrangement processes of fission following fusion, and of quasifission, are significant tests of models of nuclear dynamics. Experimental approaches to determine characteristic times, and their consistency, are discussed.

Long lifetime components in the decay of excited super-heavy nuclei

“…Figure 1 presents, for the heaviest system presently studied at an energy above the Coulomb barrier, 48 Ti + 238 U at 289 MeV (E/B ∼ 1.1), the crosssection d 2 σ dθ CM ×dM R as a function of the center-of-mass scattering angle θ CM and of M R , the ratio of fragment mass to compound nucleus mass. The minimum cross-sections observed for symmetric splittings at any angle confirm for this system the vanishing of symmetric fission already inferred from studies on lighter systems [3,4,7]. For mass asymmetric splittings, the angular distributions clearly present maxima between 30 and 90 • for M R < 0.5 (90 and 150 • for M R > 0.5), indicating reactions lasting less than the rotational period.…”

“…Mass-angle distributions for heavy systems have been recently studied at the Heavy Ion Accelerator Facility at the Australian National University. In these experiments [4,7], the two coincident fragments from binary reactions were measured by large area position sensitive multiwire proportional counters allowing the determination of the detection angle and of the mass asymmetry in the DOI: 10.1051/ C Owned by the authors, published by EDP Sciences, 2013 , / exit channel. Figure 1 presents, for the heaviest system presently studied at an energy above the Coulomb barrier, 48 Ti + 238 U at 289 MeV (E/B ∼ 1.1), the crosssection d 2 σ dθ CM ×dM R as a function of the center-of-mass scattering angle θ CM and of M R , the ratio of fragment mass to compound nucleus mass.…”

Mass, total kinetic energy, and neutron multiplicity correlations in the binary fragmentation of Ti50+Pb208 at 294 MeV bombarding energy

“…As discussed in Refs. [27,29,30], ν pre should be almost independent from TKE in the case of fusion-fission. An increase of ν pre with increasing TKE was also reported in the case of a reaction induced by 16,18 O and 36,40 Ar projectiles [27,29] and was explained with the recoil effect related to the evaporated particles [27,31].…”

Measurement of the fusion probability,PCN, for hot fusion reactions

“…There have also been a number of attempts [25,44,46,47] to make semi-empirical estimates of P CN using one or another models for σ capture , W sur and using measured values for σ EVR to get values of P CN for both hot and cold fusion reactions. Other aspects of quasifission , such as the time scale and the role of deformation effects in the entrance channel have been treated [38,[48][49][50]. Contradictory results have been obtained both experimentally [13] and theoretically [11,12] as to the expected dependence of P CN upon excitation energy.…”