Emission temperatures in 40Ar+ 197Au reactions in the limiting fragmentation regime

Apparent emission temperatures of ⁴He and ⁵Li fragments were deduced for the reaction ⁴⁰Ar+ ¹⁹⁷Au at E/ A=200 MeV from the relative population of excited states. Compared to previous measurements at E/ A=60 MeV, the average emission temperatures increases by less than 2 MeV to a value of about 6 MeV. QMD calculations indicate that the momentum distribution of the nucleons forming a fragment is determined at a point where the system is still close to normal nuclear density and that they do not reflect the local momentum distribution of the surrounding nucleons. The simulations suggest that the observed low emission temperatures are a consequence of the dynamics of the fragment formation process.