Previous studies of nucleus-nucleus bremsstrahlung within the microscopic cluster model made use of a simplified current version of the electric transition operators, neglecting the meson exchange currents. The present microscopic cluster model relies on operators based on the charge density derived from an extension of the Siegert theorem valid for arbitrary photon energy. A part of the meson exchange current effects is then implicitly included in this approach. Divergence problems in matrix elements are avoided. The model is applied to the $\alpha +\alpha$ system at low photon energy for which experimental data are available. In particular, good agreement is obtained with data about on- and off-resonance $4^{+}\to 2^{+}$ transitions. The differences between the charge and current approaches are discussed on this example.

• Received 8 March 2013

DOI:https://doi.org/10.1103/PhysRevC.88.024602