In-medium effects for nuclear matter in the Fermi-energy domain

Background: By looking specifically at free nucleons (here protons), we present for the first time a comprehensive body of experimental results concerning the mean free path, the nucleon-nucleon cross-section and in-medium effects in nuclear matter.Purpose: Using the large dataset of exclusive measurements provided by the 4π array INDRA, we determine the relative degree of stopping as a function of system mass and bombarding energy. We show that the stopping can be directly related to the transport properties in the nuclear medium.Methods: We perform a systematic study of protons nuclear stopping in central collisions for heavy-ion induced reactions in the Fermi-energy domain, between 15A and 100A MeV.Results: It is found that the mean free path exhibits a maximum at λNN=9.5±2 fm, around Einc=35A MeV incident energy and decreases toward an asymptotic value λNN=4.5±1 fm at Einc=100A MeV.Conclusions: After accounting for Pauli blocking of elastic nucleon-nucleon collisions, it is shown that the effective in-medium NN cross section is further reduced compared to the free value in this energy range. Therefore, in-medium effects cannot be neglected in the Fermi-energy range. These results bring new fundamental inputs for microscopic descriptions of nuclear reactions in the Fermi-energy domain. © 2014 American Physical Society.