Quantum tunneling of a complex systems: effects of finite size and   intrinsic structure
  A simple model is considered to study the effects of finite size and internal structure in the tunneling of bound two-body systems through a potential barrier. It is demonstrated that these effects are able to increase the tunneling probability. Applications may include nuclear fusion,hydrogen atom and Cooper pair tunneling. 
V.V. Flambaum, V.G. Zelevinsky