Formation and decay of toroidal and bubble nuclei and the nuclear equation of state

Multifragmentation, following the formation of toroidal and bubble nuclei, is observed with an improved Boltzmann-Uehling-Uhlenbeck model for central ⁹²Mo+⁹²Mo collisions. With a stiff equation of state, simultaneous explosion into several nearly equal fragments in a ringlike manner occurs due to the formation of metastable toroidal nuclei. In contrast, with a soft equation of state, simultaneous explosion into several nearly equal fragments in a volumelike manner occurs due to the formation of metastable bubble nuclei. Experimental signatures for the formation of these exotic shapes are discussed.