Description
The formation of new superheavy elements (atomic number Z > 103) is one of the major achievement of nuclear physics. The exceptionally rare outcome of two nuclei colliding and forming a new compound nucleus faces strong competition from orders-of-magnitude more likely processes, including quasifission. Quasifission involves the reseparation of the the system into two fragments after capture, but prior to compound nucleus formation.
There is no fundamental model that can predict the suppression of compound nucleus formation (and hence superheavy element formation) due to quasifission, and so we must rely on empirical observations to determine the optimal reaction for forming new superheavy elements beyond element 118.
In superheavy element synthesis reactions, there is a long-observed quasifission mass yield peak near 208Pb, initially attributed to the doubly-magic nature of 208Pb diverting the evolution of the system from the formation of a compound nucleus.
However, an alternate explanation attributes the peak at 208Pb to a decrease in yield of two-body quasifission outcomes heavier than 208Pb due to the high probability that these heavy fragments will fission, producing a net three-body outcome called “sequential fission”. The missing yield produces an anomalous peak near 208Pb when only two fragments are measured.
In this talk I present the results of the first direct measurement of the three-body reaction outcomes of 50Ti with 238U, 244Pu, 248Cm, and 249Cf (forming elements 114--120) at the Heavy Ion Accelerator Facility at the Australian National University. I will discuss the identification of three-body sequential fission events. When combined with the two-body quasifission outcomes there is no evidence of increased yield at 208Pb. This overturns decades of (mis)-understanding of quasifission dynamics, enabling new insights into the processes of mass and kinetic-energy equilibration during superheavy element formation.
| I am the presenting author | Yes |
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