Direct observation of the superallowed α decay of 104Te

Alpha particle radioactivity is one of the most striking evidence for the existence of cluster structures in atomic nuclei. During the decay process, a preexisting α particle tunnels through the potential barrier formed by the residual nucleus [1,2]. The degree of preformation of the α particle, a strongly bound system of two protons and two neutrons, is extracted from the data by dividing the α-decay probability by the barrier penetrability for a given particle energy. The preformation probability changes rapidly near nuclear shell closures, which is direct evidence that clustering is connected to nuclear structure [3]. Enhanced preformation was observed in the lightest α-particle emitters, spherical tellurium and xenon isotopes decaying to magic isotopes of tin. Here, we show the most extreme case of α-particle preformation from the measurement of the decay of tellurium-104. With a half-life of 7.2 ^+2.3 _-1.5 nanoseconds, tellurium-104 is the fastest ground state α-emitting nucleus known to date. The deduced preformation demonstrates that the enhancement is greater for tellurium-104 than for any other nucleus. One nuclear model that can explain our observation postulates that the α particle can exist only in the low nuclear matter density regions on the surface of the nucleus. The uniquely high preformation for tellurium-104 is attributed to its relation to doubly-magic tin-100, creating conditions conducive to form an α particle.