Collinear cluster tri-partition: Kinematics constraints and stability of collinearity

Abstract

Background: A new mode of nuclear fission has been proposed by the FOBOS collaboration, called Collinear Cluster Tri-partition (CCT), suggesting that three heavy fission fragments can be emitted perfectly collinearly in low-energy fission. This claim is based on indirect observations via missing-energy events using the 2v2E method. This proposed CCT seems to be an extraordinary new aspect of nuclear fission. It is surprising that CCT escaped observation for so long given the relatively high reported yield, of roughly 0.5% relative to binary fission. These claims call for an independent verification with a different experimental technique.Purpose: Verification experiments based on direct observation of CCT fragments with fission fragment spectrometers require guidance with respect to the allowed kinetic energy range, which we present in this paper. Furthermore, we discuss corresponding model calculations which, if CCT is found in such verification experiments, could indicate how the breakups proceed. Since CCT refers to collinear emission, we also study the intrinsic stability of collinearity.Methods: Three different decay models are used that together span the timescales of three-body fission. These models are used to calculate the possible kinetic energy ranges of CCT fragments by varying fragment mass splits, excitation energies, neutron multiplicities and scission-point configurations. Calculations are presented for the systems 235 U(n th , f) and 252 Cf(sf), and the fission fragments previously reported for CCT, namely isotopes of the elements Ni, Si, Ca and Sn. In addition, we use semi-classical trajectory calculations with a Monte-Carlo method to study the intrinsic stability of collinearity.Results: CCT has a high net Q-value, but in a sequential decay, the intermediate steps are energetically and geometrically unfavorable or even forbidden. Moreover, perfect collinearity is extremely unstable, and broken by the slightest perturbation.Conclusions: According to our results, the central fragment would be very difficult to detect due to its low kinetic energy, raising the question of why other 2v2E experiments could not detect a missingmass signature corresponding to CCT. Considering the high kinetic energies of the outer fragments reported in our study, direct-observation experiments should be able to observe CCT. Furthermore, we find that a realization of CCT would require an unphysical fine-tuning of the initial conditions. Finally, our stability calculations indicate that, due to the pronounced instability of the collinear configuration, a prolate scission configuration does not necessarily lead to collinear emission, nor does equatorial emission necessarily imply an oblate scission configuration. In conclusion, our results enable independent experimental verification and encourage further critical theoretical studies of CCT.

Examination of evidence for collinear cluster tri-partition

“…9(b) in Ref. [5]) are identical to the ones calculated by Vijiayaraghavan et al [16] (see Fig. 6 of Ref.…”

“…The detailed analysis of the CCT regarding kinematic constraints and stability of collinearity was proposed in Ref. [5]. Three different models were under consideration.…”

“…Completely new results obtained in our experiments suggested independent experimental verification. To perform such an experiment at the mass-separator Lohengrin (ILL, Grenoble, France), estimation of the expected parameters of the CCT products was performed in the recent work [5]. The parameters should be compared with our experimental findings, only partially published so far.…”

True ternary fission and the rotation effect

“…It is no coincidence that in Ref. [17] the authors doubted a possibility of a "perfectly" collinear flight in the case of three massive fragments. At the same time, it is known that there is a small fraction ∼10 percent of polar alpha particles, emitted along the fission axis (e.g.…”

Scission Point Calculations and Physical Treating of the 'Ni-bump' in 252Cf (sf)

“…Later we switched to solid-state detectors, namely timing detectors, on the microchannel plates and the mosaics of PIN diodes (COMETA setup [2] and the similar ones [3]). Even Estimation of the expected parameters of the CCT products was performed in the recent theoretical works [5][6][7]. The results obtained were taken into account in our model of the most populated CCT mode known as "Ni-bump".…”