Examination of evidence for collinear cluster tri-partition

Pyatkov, Yu. V. ; Kamanin, D. V. ; Alexandrov, A. A. ; Alexandrova, I. A. ; Goryainova, Z. I. ; Malaza, V. ; Mkaza, N. ; Kuznetsova, E. A. ; Strekalovsky, A. O. ; Strekalovsky, O. V. ; Zhuchko, V. E. (2017)

CITATION: Pyatkov, Yu. V., et al., 2017. Examination of evidence for collinear cluster tri-partition. Physical Review C, 96(6):1-16, doi:10.1103/PhysRevC.96.064606.

The original publication is available at https://journals.aps.org/prc

Article

Background: In a series of experiments at different time-of-flight spectrometers of heavy ions we have observed manifestations of a new at least ternary decay channel of low excited heavy nuclei. Due to specific features of the effect, it was called collinear cluster tri-partition (CCT). The obtained experimental results have initiated a number of theoretical articles dedicated to different aspects of the CCT. Special attention was paid to kinematics constraints and stability of collinearity. Purpose: To compare theoretical predictions with our experimental data, only partially published so far. To develop the model of one of the most populated CCT modes that gives rise to the so-called “Ni-bump.” Method: The fission events under analysis form regular two-dimensional linear structures in the mass correlation distributions of the fission fragments. The structures were revealed both at a highly statistically reliable level but on the background substrate, and at the low statistics in almost noiseless distribution. The structures are bounded by the known magic fragments and were reproduced at different spectrometers. All this provides high reliability of our experimental findings. The model of the CCT proposed here is based on theoretical results, published recently, and the detailed analysis of all available experimental data. Results: Under our model, the CCT mode giving rise to the Ni bump occurs as a two-stage breakup of the initial three body chain like the nuclear configuration with an elongated central cluster. After the first scission at the touching point with one of the side clusters, the predominantly heavier one, the deformation energy of the central cluster allows the emission of up to four neutrons flying apart isotropically. The heavy side cluster and a dinuclear system, consisting of the light side cluster and the central one, relaxed to a less elongated shape, are accelerated in the mutual Coulomb field. The “tip” of the dinuclear system at the moment of its rupture faces the heavy fragment or the opposite direction due to a single turn of the system around its center of gravity. Conclusions: Additional experimental information regarding the energies of the CCT partners and the proposed model of the process respond to criticisms concerning the kinematic constraints and the stability of collinearity in the CCT. The octupole deformed system formed after the first scission is oriented along the fission axis, and its rupture occurs predominantly after the full acceleration. Noncollinear true ternary fission and far asymmetric binary fission, observed earlier, appear to be the special cases of the decay of the prescission configuration leading to the CCT. Detection of the 68–72Ni fission fragments with a kinetic energy E<25MeV at the mass-separator Lohengrin is proposed for an independent experimental verification of the CCT.

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