Dynamical dipole $\gamma$ radiation in heavy-ion collisions on the basis of the quantum molecular dynamics model

Dynamical dipole $\gamma$-ray emission in heavy-ion collisions is explored in the framework of the quantum molecular dynamics model. The studies are focused on systems of ${}^{40}$Ca bombarding ${}^{48}$Ca and its isotopes at different incident energies and impact parameters. Yields of $\gamma$ rays are calculated and the centroid energy and dynamical dipole emission width of the $\gamma$ spectra are extracted to investigate the properties of $\gamma$ emission. In addition, sensitivities of dynamical dipole $\gamma$-ray emission to the isospin and the symmetry energy coefficient of the equation of state are studied. The results show that detailed study of dynamical dipole $\gamma$ radiation can provide information on the equation of state and the symmetry energy around the normal nuclear density.