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Properties of highly excited nuclei -- phase transition It is known that highly excited nuclei run into instabilities, e.g. they decay into many fragments. This process, named multifragmentation is investigated with several dedicated experimental installations, one of those being the ALADIN magnet at GSI. From the observation of relatively neutron-rich heavy nuclides, measured at the fragment separator with its capability to fully identify the reactions products in mass number A and nuclear charge Z, we concluded that thermal instabilities (simultaneous break-up) already set in before multifragmentation occurs. These results were analysed quantitatively by the use of the isospin thermometer. According to this method, yields of light fragmentation residues, or more precisely their N/Z ratios (see figure below), carry the information on the temperature, the system reaches after the break-up. This temperature corresponds to the limiting temperature above which a fully equilibrated compound nucleus cannot exist. The measured data support a value of Tlim ~ 5 MeV.
Apart of their importance for understanding the fundamental properties of nuclear matter, these kind of studies can be essential for better understanding the production mechanisms which create the high-energetic particles that we observe as cosmic rays, but also for the applications in nuclear technology. More information on the isospin thermometer can be found here. More information on the liquid-gas phase transition in nuclei on this WEB page.
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