Experimental approaches to intermediate energy. Heavy ion collisions: nuclear interferometry and fragment detection

In the last two decades, nuclear reactions induced by beams of heavy ions have proved to be a tool to investigate nuclear matter behaviour far away from the ordinary ground state. In the late stage of a heavy ion collision at intermediate energies the system is composed of nucleons and fragments of various masses. The abundant production of nuclear fragments, on a time scale much shorter than the one required for the sequential decay of the system, could be the signal for a liquid-gas phase transition. One possible experimental approach to the understanding of the complicated dynamical scenario in a heavy ion collision is to measure fragment distributions. Detection of very heavy recoiling target fragments is an interesting possibility opened up by the combination of intense beams and extremely thin gas jet targets available at storage rings. Such recoils carry much information about the dynamics and the momentum transfer of the reaction and can allow the determination of the impact parameter and the reaction plane. Time of flight - energy detectors telescopes have proved to be suitable for the detection of low energy (≤0.3 A MeV) heavy (A≥8) recoiling fragments ΔΕ-E silicon telescopes can instead be used for detection of high energy (≥ A MeV) fragments. Information on the space-time characteristics of a nuclear source can be obtained with the measurement of correlations between small relative momentum particles, i.e. with nuclear intensity interferometry technique. The correlation function, originating from the interplay of quantum interference effects and final state interactions can be used to extract source sizes and to probe the first instants of the evolution of a heavy ion collision. (35 refs.)