?Slow? residues observed in the reaction20Ne+208Pb at E/A=8.6, 11.4 and 15.0 MeV/u

Abstract

Abstract. Velocity distributions of heavy residues ARes>Atar, ZRe s>Zta r identified by means of c~ spectroscopy, have been investigated at the velocity filter SHIP in reactions 2~ +2~ at projectile energies E/ A=8.6, 11.4 and 15.0MeV/u. Besides products from complete or nearly complete fusion, characterized by velocity distributions peaking at V/VcN~0.8-1.O, heavy residues with mean velocities of about half of the compound nucleus velocity were observed. The Z-distribution of this component was found to peak at Z = 87. It is interpreted as residues from fusion of target nuclei with projectile fragments produced by nearly symmetric break-up. The experimental results were compared with predictions of theoretical models: cross sections for incomplete fusion were calculated using the sum-rule model of Wilcynski et al., while residue cross sections were calculated using the evaporation code HIVAP. A fair agreement between experimental and calculated mass distributions of heavy residues and transferred projectile fragments is achieved if an energy dissipation of -~ 23 % (at E/A = 8.6 MeV/u) and ~ 8% (at E/A = 11.4 MeV/u) of the incident projectile energy is introduced. The observed peak of the Z-distribution at Z = 87 is predominantly effected due to a higher fission probability of products with Z>87 during the deexcitation process and experimental limitations in the identification of products with Z < 86 by means of ~ spectroscopy, which cause a decrease of the observed production rates towards lower Z.

Evidence for incomplete fusion on the12C +208Pb and13C +207Pb reactions in above-barrier energies

“…The process has been studied for more than three decades and observed mainly for light projectiles (Z 12, A 25). The main features of the studies were the measurement of the escaping fragments, partly in coincidence with fusion products [15] or investigation of the kinematic properties of the reaction products [16,17].…”

Peculiarities of quasifission reactions in heavy ion collisions

“…In the experiment discussed in Ref. [19], the maximum value of the velocity distribution of the "slow" Fr 213 isotope was found to be v Fr /v CN ≃ 0.5. This leads to the conclusion that the yield of "slow" evaporation residues observed in the Ne 20 + Pb 208 reaction at the projectile energy E/A = 8.6 MeV/u comes from quasifission process.…”

“…[19], 1 where the velocity decrease was observed for the massive target-like products which are considered as the evaporation residues being registered by the velocity filter SHIP at GSI. At some values of orbital angular momentum L, the DNS formed after the capture of the Ne 20 nucleus by the Pb 208 target nucleus can rotate around the axis going through its centre-ofmass and breaks down into two fragments.…”

MOCADI_FUSION: Extension of the Monte-Carlo code MOCADI to heavy-ion fusion–evaporation reactions

“…It has been widely used for the synthesis [6] and the spectroscopy [24] of super-heavy elements, for the discovery of the proton radioactivity [25] and for fusion reaction studies around [26] and far above the Coulomb barrier [27]. More recently, a double Penning trap system, SHIPTRAP [16], was installed behind the SHIP focal plane to perform precise mass measurements of nuclei along the rp-process [12], n-deficient nuclei in the rare-earth region close to the proton drip line, and super-heavy nuclides.…”