Physicists at the University of Tennessee, Knoxville and their colleagues have measured the lifetime and decay energy of tellurium-104, capturing a 7.2-nanosecond half-life that sheds light on a century-old nuclear physics question regarding how alpha particles form inside heavy atomic nuclei before escaping via quantum tunneling.
Inside the Shortest-Lived Alpha Emitter
Alpha radioactivity was discovered more than 125 years ago, yet the precise origin of the emitted alpha particle—a tightly bound cluster of two protons and two neutrons—remains an active puzzle in nuclear physics. Heavy nuclei typically feature a relatively uniform distribution of matter. That structural reality forces researchers to ask how local clustering occurs right before emission, a phase known as preformation.
According to research published in Nature and highlighted by the University of Tennessee, Knoxville and the Department of Energy’s Oak Ridge National Laboratory, tellurium-104 represents a unique laboratory for studying this phenomenon. The experimental team, led by UTK Professor Robert Grzywacz at the Radioactive Isotope Beam Factory (RIBF) at RIKEN in Japan, tracked the fleeting isotope to measure its exact decay properties.
Synthesizing tellurium-104 is a formidable logistical and technical hurdle. The isotope lives for just nanoseconds and emerges from the radioactive decay of xenon-108, which itself demands advanced particle acceleration facilities to produce. To bypass this bottleneck, the RIKEN team utilized four coupled cyclotrons to accelerate a beam of xenon-124 into a beryllium target. The resulting collisions generated xenon-108 fragments, whose subsequent decay chain populated tellurium-104 before cascading down to tin-100.
Weighing the Preformation Probability
The experimental results yielded a half-life of 7.2 nanoseconds for tellurium-104, confirming it as the shortest-lived known alpha particle radioactive nucleus. When the research team corrected this ultra-short half-life against the available decay energy, the resulting alpha particle preformation probability was substantially higher than theoretical models predicted.
“We have measured the lifetime and energy of this decay and found that the preformation probability is much larger than expected based on predictions, which used available experimental knowledge,” Grzywacz noted regarding the findings.
For decades, nuclear physicists have pointed to polonium-212 decaying into lead-208 as the primary benchmark for enhanced alpha preformation. However, tellurium-104 blows past previous baselines. Its preformation probability is roughly ten times higher than that observed in the well-studied polonium system, making it an extraordinary outlier across the nuclear landscape.
Theoretical physicists in the 1960s hypothesized that tellurium-104 might function momentarily as a molecular-like configuration composed of an alpha particle bound to a tin-100 core. Tin-100 is classified as a doubly magic nucleus, meaning it’s strongly bound. Grzywacz and his colleagues attribute the unusually high preformation rate of tellurium-104 directly to this structural proximity to doubly magic tin, which creates highly favorable conditions for an alpha cluster to coalesce.
Decades of Research at Oak Ridge
While the definitive measurements were captured at RIKEN’s RIBF facility, the intellectual groundwork was laid over decades of experimentation in the United States. Researchers at the Department of Energy’s Oak Ridge National Laboratory built a long-standing reputation for exploring alpha-emitting nuclei clustered near the tin-100 closed shell.
Key historical milestones include work done in 2006, when Grzywacz teamed up with ORNL physicists Krzysztof Rykaczewski and Carl Gross to utilize the Recoil Mass Spectrometer at the historic Holifield Radioactive Ion Beam Facility (HRIBF). That foundational instrumentation allowed researchers to probe the extreme fringes of the nuclear chart, setting the stage for modern beam-line experiments.
By capturing precise data on tellurium-104, modern physics moves one step closer to decoding how nuclear matter organizes itself locally under extreme conditions. The findings offer a concrete anchor for refining theoretical models of quantum tunneling and nuclear structure across hundreds of unstable isotopes.
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