Dynamical dipole mode in fusion reactions.

We investigated the dynamical dipole mode, related with entrance channel charge asymmetry effects, in the ⁴⁰Ar+⁹²Zr and ³⁶Ar+⁹⁶Zr fusion reactions at E_lab = 15.1 A and 16 A MeV, respectively. These reactions populate, through entrance channels having different charge asymmetries, a compound nucleus in the A = 126 mass energy region, identical spin distribution at an average excitation energy of about 280 MeV. The compound nucleus average excitation energy and average mass were deduced by the analysis of the light charged particle energy spectra. By studying the γ-ray energy spectra and the γ-ray angular distributions of the considered reactions, the dynamical nature of the prompt radiation related to the dynamical dipole mode was evidenced. The data are compared with calculations based on a collective bremsstrahlung analysis of the reaction dynamics. [ABSTRACT FROM AUTHOR]