Tantalum stands out as one of the most uncommon elements on Earth, boasting several stable forms known as isotopes. Among these, the Ta-180 isotope is particularly rare, existing naturally in an excited state that sets it apart. In such states, the energy levels of an atom’s protons or neutrons are unusually high. Despite the theoretical possibility, the radioactive decay of Ta-180m in its excited state has yet to be observed. Currently, researchers are undertaking experiments aimed at detecting this decay, believed to have a lifespan vastly exceeding the universe’s age.
The study of nuclei in excited states sheds light on the deformation of nuclei under these conditions. Nuclear physicists have delved into how these short-lived isotopes, or isomers, change shape and form. Yet, the decay of Ta-180m remains largely unexplored. This isomer’s remarkable stability poses a challenge to existing nuclear theories and models. By attempting to measure its decay, scientists are presented with a unique chance to advance nuclear theory. A groundbreaking experiment now offers the sensitivity needed to observe the predicted half-lives, setting new records in the study of nuclear isomers.
In this ambitious project, the MAJORANA ultra-low background facility at the Sanford Underground Research Facility in South Dakota underwent significant modifications. The team introduced a tantalum sample much larger than any used in previous experiments. Over a year, they gathered data with germanium detectors known for their superior energy resolution. They also developed new analysis techniques to identify various expected decay signatures. These efforts have set new sensitivity records, with limits now within the 10^18 to 10^19 years range, bringing theoretical half-life predictions within reach for the first time.
Although the decay process remains unobserved, these advancements have significantly improved existing limits. Moreover, they have enabled researchers to rule out certain possibilities regarding the properties of potential dark matter particles.
For more information, you can reach out to Ralph Massarczyk and Sam Meijer at the Los Alamos National Laboratory. This research received support from several institutions, including the Laboratory Directed Research and Development programs at various national laboratories, the Department of Energy, the National Science Foundation, and others.
The findings of this research have been documented in a publication by Arnquist, I.J., and the MAJORANA Collaboration in Physical Review Letters, highlighting the constraints on the decay of 180mTav. For further reading, several related articles and highlights are available, offering insights into this groundbreaking research.