'Superallowed' alpha decay seen for the first time – Physics World
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Nuclear physics
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Home »<br>Particle and nuclear » Nuclear physics » ‘Superallowed’ alpha decay seen for the first time
Nuclear physics
Research update
‘Superallowed’ alpha decay seen for the first time
25 Jun 2026 Isabelle Dumé
Tunnelling out Illustration of the alpha decay of tellurium-104 over the RIBF at RIKEN. (Courtesy: Robert Grzywacz/University of Tennessee)">
Tunnelling out Illustration of the alpha decay of tellurium-104 over the RIBF at RIKEN. (Courtesy: Robert Grzywacz/University of Tennessee)
Physicists headed up by a team at the University of Tennessee, Knoxville, and the Radioactive Isotope Beam Factory (RIBF) at RIKEN in Japan say they have measured the alpha decay of tellurium-104 for the first time. The feat could help us better understand how alpha particles form inside atomic nuclei, which is one of the least understood problems in nuclear science.
Alpha radioactivity was discovered over 125 years ago and it is the process whereby an atomic nucleus emits an alpha particle, which is a helium nucleus consisting of two protons and two neutrons that are strongly bound. The alpha particle exits the nucleus by quantum-mechanical tunnelling through the energy barrier surrounding the nucleus. While this model broadly explains the lifetimes of radioactive nuclei, a big question remains, however, says study lead Robert Grzywacz at the University of Tennessee, Knoxville. This is: how do alpha particles form in the nucleus and where can they exist as “pre-formed” structures inside it before they leave?
Tellurium-104 is particularly suited to studying alpha radioactivity, he says, because it is predicted to have the highest chance of pre-forming alpha particles of all heavy nuclei. “Such a strong enhancement of preformation shouldn’t be possible in theory because the matter in heavy nuclei is uniformly distributed,” Grzywacz explains. “There must, therefore, be an extra mechanism that causes alpha particles to locally ‘clump’ or ‘cluster’.”
In their experiments, he and his colleagues set about measuring the alpha particles produced by tellurium-104. This was no easy task because this isotope of tellurium can only be observed during the decay of xenon-108, which itself is extremely difficult to make in the laboratory.
Pulses of alpha particles
The researchers did their work at Japan’s RIKEN accelerator complex, which consists of four coupled cyclotrons that accelerate a beam of xenon-124 onto a beryllium production target. The collisions between the two produces xenon-108 and then tellurium-104. The tellurium-104 finally decays into tin-100.
Grzywacz and co-workers say they succeeded measuring pulses of alpha particles produced in short succession by the tellurium-104. They measured the half-life...