Density and thermalization in heavy-ion reactions at the geometry of vanishing flow

The heavy-ion reactions at intermediate energies provide a unique possibility of hot and dense nuclear matter under the extreme conditions of temperature and density. Various observables like multifragmentation, collective transverse in-plane flow and particle production have been proposed in this direction to study the properties of nuclear matter like nuclear equation of state and in medium nucleon-nucleon cross-section. Out of these observables, collective flow has been found to be one of the most sensitive towards the above mentioned properties as well as towards incident energies, impact parameter and colliding systems. Collective transverse in-plane flow increases with impact parameter, reaches maximum at semi-central collisions and then again starts decreasing at peripheral collisions. The value of impact parameter where collective flow vanishes (crosses zero) is called geometry of vanishing flow (GVF). The system size dependence of GVF has been found to be sensitive to in medium nucleon-nucleon cross-section and is insensitive to equation of state and momentum dependent interactions. In present paper, the density and thermalization at GVF have been studied. Isospin quantum molecular dynamics (IQMD) model is used for the study