Fusion probability of massive nuclei in reactions leading to heavy composite nuclear systems

R N Sagaidak

doi:10.1051/epjconf/201922301052

Abstract

Reactions between massive nuclei show a considerable reduction in fusion-evaporation cross-sections at the Coulomb barrier according to the comparison of experimental values with those calculated by barrier passing (BP) and statistical model (SM) approximations. Reduced fusion cross-sections corresponding to fusion probability PCN<1 are accompanied by a high probability of deep-inelastic and quasi-fission processes arising on the way to fusion. At the same time, the excitation functions for evaporation residues (ERs) obtained in very mass-asymmetric projectile-target combinations are well described in the framework of the BP model (assuming PCN=1) and SM approximations. In the framework of SM, the survivability of produced heavy nuclei can be described with the use of adjusted macroscopic fission barriers. Fusion suppression appears in less asymmetric combinations, for which PCN values can be estimated using survivability obtained for very asymmetric ones leading to the same CN. An attempt was made to systemize the PCN data derived from different projectile-target combinations leading to ERs in the range from Pb to the most heavies, which are compared withPCN values obtained in fission experiments.

Highlights

Available cross-section data on the fusion, fission and evaporation residues (ERs) production, which are obtained in very mass-asymmetric projectile-target combinations, can be well described in the framework of the barrier passing (BP) and statistical model (SM) approximations realized in the HIVAP code [2]
In heavy ion (HI) experiments, PCN values can be derived with the detection of fission fragments (FFs) and subsequent comparison of a total FF yield including deep-inelastic events with the FF yield assigned to true CN-fission
It is the result of a small value of this component (⁓0.4 MeV) for Hs fission barriers used in calculations. Neglecting this component leads to PCN=1, but this assumption is in contradiction to a smooth drop of the macroscopic fission barriers to zero with an increase in the CN fissility and to a trend implying a general reduction in PCN with the same change

Summary

Motivation and approach

Reactions with massive nuclei show a considerable reduction in fusion at the Coulomb barrier. Most of the models reproduce measured σER quite well, but they give PCN values differed from each other within several orders of the magnitude [1] Such a difference implies a similar distinction in Wsv. At the same time, available cross-section data on the fusion, fission and ER production, which are obtained in very mass-asymmetric projectile-target combinations, can be well described in the framework of the BP and statistical model (SM) approximations realized in the HIVAP code [2] (see examples in [3]). Fitting calculated excitation functions to the measured ones obtained in very asymmetric projectiletarget combinations by adjusting fission barriers, one can get estimates of Wsv. Fusion suppression corresponding to PCN

PCN from fission study

PCN from ER cross sections

PCN systematics and summary