Tantalum, one of the rarest elements, is known for having multiple stable isotopes. Among these isotopes, Ta-180 stands out as the least abundant and is found naturally in a long-lived excited state, a characteristic that sets it apart from other elements.
Despite being energetically possible, the radioactive decay of the excited state in Ta-180m has never been observed. This poses a significant challenge to researchers who are now conducting experiments to measure this decay, which is expected to have a lifetime approximately 1 million times longer than the age of the universe.
The decay of excited states of nuclei, such as Ta-180m, provides valuable insights into how nuclei deform when in those states. While nuclear physicists have extensively studied variations in shape and the formation of short-lived isotopes, known as isomers, the decay of Ta-180m remains largely unexplored. This presents a unique opportunity to challenge and contribute to existing theories and models of nuclear structure and decay.
The Experiment at Sanford Underground Research Facility
Scientists have recently devised an experiment at the MAJORANA ultra-low background facility at the Sanford Underground Research Facility in South Dakota to measure the decay of Ta-180m. This experiment involved introducing a significantly larger tantalum sample than any previously used, and collecting data over a year using germanium detectors with exceptional energy resolution.
The experiment has led to the establishment of the longest limits ever achieved in nuclear isomer studies, falling within the range of 10^18 to 10^19 years. This level of sensitivity marks a significant advancement in the field, as it allows researchers to reach predicted half-life values from nuclear theory for the first time.
While the decay process in Ta-180m has not yet been observed, the advancements made through this experiment have significantly enhanced existing limits by one to two orders of magnitude. Additionally, researchers have been able to dismiss certain parameter ranges associated with potential dark matter particles, further contributing to the field of nuclear physics.
The groundbreaking experiment to measure the decay of Ta-180m represents a unique challenge and opportunity for nuclear physicists to push the boundaries of existing theories and models. The unprecedented sensitivity achieved through this research has paved the way for new discoveries and enhanced understanding of nuclear structure and decay.
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