Cooling Dynamics in Multi-fragmentation processes
  Fragment energy spectra of neutron deficient isotopes are significantly more energetic than those of neutron rich isotopes of the same element. This trend is well beyond what can be expected for the bulk multi-fragmentation of an equilibrated system. It can be explained, however, if some of these fragments are emitted earlier through the surface of the system while it is expanding and cooling. 
T.X. Liu, W.G. Lynch, M.J. van Goethem, X.D. Liu, R. Shomin, W.P. Tan,   M.B. Tsang, G. Verde, A. Wagner, H.F. Xi, H.S. Xu, ...