CORDIS provides links to public deliverables and publications of HORIZON projects.
Links to deliverables and publications from FP7 projects, as well as links to some specific result types such as dataset and software, are dynamically retrieved from OpenAIRE .
Deliverables
The analysis of mass, charge and energy distributions of fragments from nuclear fission in terms of distinct modes has been introduced many years ago by experimental physicists with the aim to systematise observational facts. More recently these modes have received a more theoretical basis. Calculating the multi-dimensional potential energy surface of a deforming nucleus on its was to scission it has been realised that structures like valleys and ridges in the energy landscape are closely linked to the phenomenological modes. Currently much work is devoted to the identification of fission modes and the study of their properties, both in theory and experiment.
The present project is a comparative study of the mode characteristics of several Cm isotopes for both, spontaneous fission and thermal neutron induced fission. The reactions 244Cm(sf), 248Cm(sf) and 245Cm(n,f) have been investigated. As a reference the fission reaction 252Cm(sf) was analysed in parallel. The experimental techniques employed were time-of-flight measurements of fragment velocities (whence energies and masses) and the determination of nuclear charges for fragments and ternary charged particles of given mass and energy as identified by an electromagnetic separator. In addition, for the reaction 248Cm(sf) a detailed study of neutron emission from the fragments has been started.
Research on the fission properties of Cm has been hampered since decades due to the shortage of isotopically pure samples. Therefore, even knowledge on basic features like mass and energy distributions of fragments from fission of Cm isotopes is poor. The present work has solved some of the existing inconsistencies in the literature but not all.
For the mass yields Y(A) from 244Cm(sf) the present results agree as to the gross features with what is reported by other authors but the situation is far from being satisfactory as to the details of the distributions. The yields for the reaction 245Cm(n,f) are in a better shape, and especially the very reliable data from the electromagnetic separator could now serve as a reference - at least in the measured light mass group of fragments. For the reaction 248Cm(sf) the situation is again less clear. Former results indicated that Y(A) has a pronounced structure while the present investigations have found in two independent measurements rather smooth distributions. This latter trend fits, however, much better into the systematics of mass/charge distributions of the actinides in general. An interesting observation has surfaced in the evaluation of the 248Cm(sf) data. For low excitation energies of the fragments the yield is dominated by a mode where both fragments have ground state shapes deviating from a sphere while the highest observable excitation energies are correlated to a heavy magic and spherical nucleus around 132Sn and an excessively deformed light fragment. This latter point is also clearly borne out by calculations of the potential energy surface. Surprisingly, the ternary yields measured for the 246Cm* nucleus provide further evidence for these findings. The heaviest ternary particles seen in experiment appear to be just remnants of a strongly deformed mother nucleus with two magic nuclei forming the tips - according to the theory 132Sn and 78Ni - having been set free.
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