When a heavy atomic nucleus splits into two fragments, an invisible quantum thread remains between them. This thread is entanglement: the state of one fragment is instantly linked to the state of the other, as if they were still a single whole. For the first time, physicists have precisely calculated how long and strong such a thread can be, tracing the fission process step by step.
The calculations covered seven different fission pathways. It turned out that the strength of the quantum link does not depend on how the nucleus splits — whether it stretches, flattens, or forms a neck in the middle. Instead, it is closely tied to how 'loose' the particle numbers are in the fragments. And the biggest surprise: if a fragment is a 'magic' nucleus, entanglement drops sharply. Magic nuclei are those with completely filled proton and neutron shells: they are especially stable, like a completed puzzle with no gaps.
This gives rise to an 'anti-entanglement effect': the more stable the fragment, the less it shares a quantum thread with its neighbor. This flips the conventional view of nuclear fission — now it can be studied not only by the shape of the fragments but also by the invisible links between them.
The magic nucleus tin-132 is the most stable fission fragment: its shells are filled for both protons and neutrons, so its entanglement with a partner is especially weak.