Collinear cluster tripartition of 252Cf(sf) - research status and prospects

A brief report of the series of experiments is devoted to searching for a new type of cluster radioactivity called 'collinear cluster tripartition' (CCT). The experiments were performed recently by the collaboration FLNR- JYFL both at the modified FOBOS setup and the time-of-flight spectrometer based on micro-channel plates and PIN diodes. The mother system was found to undergo ternary decay forming three fragments of comparable masses flying apart almost collinearly. Different modes of this process were revealed showing up the yields of 10-6 - 10-4 each reference to conventional binary fission. The effect observed can be naturally treated as a decay of the nuclear molecule formed by at least two magic constituents preformed in the body of the decaying system while one of the fragments is not magic. The way to observe CCT is illustrated in this report. Due to blocking of one of the light fragments one observes a pair of the collinear fragments with the considerable deficit of their total mass, which are responsible for the statistically reliable bump are also shown. By subtracting the baseline associated mostly with the scattered fragments, one obtains the peak corresponding to the missed mass of 48 amu, which can be ascribed to the double magic Ca nucleus. On the contrary to the expectations, the mode associated with the decay of 252Cf into trinity of the magic clusters Ni + Ca + Sn due its exclusive magicity turned to be not dominated. The most prominent mode actually manifested is associated with the missing mass of 44 amu and, respectively, the observed total mass of 208 amu seems to be, by its composition, the sum of 128Sn and 88Ge isotopes. The latter pair was already reported as a 'founder' of the most populated fission mode in binary fission of the 252Cf nucleus. We still do not put forward any comprehensive explanation of the physical nature of the decay properties observed in CCT of 252Cf. We prepare instead the series of experiments aimed at studying of CCT of the different low excited systems. On the other hand, from the analysis of our experiments performed with 252Cf, it seems true ternary spontaneous decay channel has been observed for the first time. (authors)