Physicists from the University of Tennessee, Knoxville, and the Radioactive Isotope Beam Factory (RIBF) in Japan have measured the alpha decay of tellurium-104 for the first time. This breakthrough could improve our understanding of how alpha particles form inside atomic nuclei, a complex issue in nuclear science.
Alpha radioactivity was discovered over 125 years ago, marking a fascinating chapter in nuclear science; it occurs when an atomic nucleus emits an alpha particle, which is a helium nucleus consisting of two protons and two neutrons.
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The alpha particle cleverly escapes the nucleus by tunneling through an energy barrier. While this illuminates the longevity of radioactive nuclei, an exciting question arises, as study lead Robert Grzywacz at the University of Tennessee, Knoxville, points out: how do alpha particles form in the nucleus, and where do they exist as “pre-formed” structures before they make their joyful exit?
Tellurium-104 is ideal for studying alpha radioactivity since it is expected to have the highest likelihood of forming alpha particles among heavy nuclei.
Grzywacz notes that this significant increase in preformation shouldn’t theoretically occur because heavy nuclei have a uniform distribution of matter. Thus, there must be an additional mechanism that causes alpha particles to gather or cluster locally.
In their experiments, he and his colleagues set about measuring the alpha particles produced by tellurium-104, a task that required both precision and patience. 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 due to its short half-life and the specialized equipment needed for its synthesis.
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The researchers faced numerous challenges in isolating the tellurium-104 alpha particles, as they had to carefully navigate the complexities of the decay process, ensuring that their experiments accounted for potential interferences and variations in readings.
Their dedication and innovative approach opened up new pathways for understanding the intricate behaviors of these isotopes in nuclear physics, potentially leading to breakthroughs in both theoretical and applied research.
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 produce xenon-108 and then tellurium-104. The tellurium-104 finally decays into tin-100.
Grzywacz and co-workers say they succeeded in measuring pulses of alpha particles produced in short succession by the tellurium-104. They measured the half-life of the radioisotope as being 7.2 ns, which is the shortest known alpha decay half-life for alpha particle emission from a heavy nucleus.
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More importantly, after accounting for the tunnelling effect with a parameter called reduced width, which distinguishes quantum tunnelling from natural alpha particle emission, they confirmed that the likelihood of an alpha particle forming in the nucleus was significantly greater than theoretical calculations suggested.
“The possibility that tellurium-104 could show such “superallowed” alpha decay was first put forward more than 60 years ago, but it has been impossible to observe experimentally”, says Grzywacz.
Researchers have been investigating this decay for over 20 years, initially at Oak Ridge National Laboratory and later at JAEA in Japan. The current experiment proposal was made in 2018 at RIKEN, but due to the COVID-19 pandemic, it was resubmitted in 2022. The experiment received a ‘very high priority’ status, with tests conducted in June 2024.
“This work will be important for understanding how alpha particles form in nuclei and will push the theory to explain where and how nuclear clusters can form”, says Grzywacz.
More than 300 nuclei, predominantly including nearly all superheavy nuclei, undergo decay through alpha particle emission. While lighter nuclei may naturally develop ‘alpha condensates’, the mechanisms by which this occurs in heavier nuclei remain unclear.
Grzywacz told Physics World that he and his colleagues will now need to measure alpha particle energies with better precision in order to constrain the preformation they have observed, a critical step that will enhance their understanding of the underlying nuclear processes.
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This enhanced precision is crucial not just for validating their exciting findings, but also for exploring the fascinating details of how alpha particles interact within atomic nuclei.
By refining their measurement techniques and utilizing advanced detection methods, the research team hopes to gain new insights that could potentially unravel mysteries of nuclear structure and stability, contributing significantly to the field of nuclear physics.
Reference: https://physicsworld.com/a/superallowed-alpha-decay-seen-for-the-first-time/
