First measurement of tellurium-104 alpha decay confirms superallowed theory

Tellurium-104 decayed by alpha emission in just 7.2 nanoseconds, the first direct observation of the long-predicted superallowed mode near doubly magic tin-100. The result gives 104Te the highest deduced alpha-particle formation probability known and makes it the fastest known ground-state alpha-emitting nucleus.

Researchers produced the decay chain at RIKEN’s Radioactive Isotope Beam Factory in Japan, where four coupled cyclotrons accelerated xenon-124 into a beryllium target. That reaction created xenon-108, which decayed to tellurium-104 and then to tin-100, a sequence that had to be tracked under extreme timing pressure because both xenon-108 and tellurium-104 survive only nanoseconds.

The Nature paper, published May 27, 2026, lands on a nucleus that nuclear physicists treat as a benchmark: 100Sn, with its closed proton and neutron shells. For more than 125 years, alpha decay has been studied in detail, yet how an alpha particle actually forms inside a heavy nucleus has remained unsettled. Tellurium-104 sits in the exact region where decade-old and even 1960s-era predictions pointed to an unusually strong, or superallowed, alpha-decay branch. Earlier neutron-deficient tellurium emitters gave the region that label.

The alpha-particle formation probability in 104Te is about twice that of known nuclei. Robert Grzywacz of the University of Tennessee said the result strengthens the case that tellurium-104 is the definitive test of alpha preformation near 100Sn and helps address “a century-old question” about where alpha particles come from inside nuclei.