Using a new mass-separator of radioactive isotopes, called the KEK Isotope Separation System (KISS), which is developed and operated by the Wako Nuclear Science Centre in the High Energy Accelerator Research Organization in Japan, an international team of experimental physicists has produced the world’s first purified beams of tantalum-187 (187Ta) — a development that could now allow for lab-based experiments on exploding stars.
Tantalum, a chemical element with the symbol Ta and atomic number 73, is a rare, hard, blue-gray, lustrous transition metal that is highly corrosion-resistant.
Natural tantalum consists of two stable isotopes: 181Ta and 180mTa. There are also 35 known artificial radioisotopes, the longest-lived of which is 179Ta with a half-life of 1.82 years. 187Ta has a half-life of around 2 min.
Tantalum is extremely difficult to vaporize, so University of Surrey’s Professor Philip Walker and colleagues had to capture radioactive tantalum atoms in high-pressure argon gas, ionizing the atoms with precisely tuned lasers.
A single isotope of radioactive tantalum could then be selected for detailed investigation.
In the study, Professor Walker and co-authors found that when produced in a metastable state nucleus of 187Ta fleetingly rotated in an irregular manner.
They discovered that 187Ta’s gamma-ray ‘fingerprint’ was characteristic of a prolate (American football) shape but simultaneously with a hint of an oblate (pancake) shape.
They believe their results hint at the possibility of tantalum’s more dramatic shape-change to a full oblate rotation which they aim to explore in detail in future experiments.
“Theory suggests that just two more neutrons could tip the shape of 187Ta from prolate to oblate, so 189Ta is an objective for future investigation,” Professor Walker said.
“However, it now seems to be a real possibility to go further and reach uncharted 199Ta, with 126 neutrons, to test the exploding-star mechanism.”
“Our KISS is a unique facility which can provide unexplored heavy nuclei, such as 187Ta, 189Ta, and 199Ta, for the studies of exotic nuclear structures,” said co-author Dr. Yoshikazu Hirayama, a researcher in the Wako Nuclear Science Centre at Japan’s High Energy Accelerator Research Organization.
“We have started to delve into the mechanism of the synthesis of elements in the universe through the nuclear studies at KISS.”
The team’s results are reported in the journal Physical Review Letters.
P.M. Walker et al. 2020. Properties of 187Ta Revealed through Isomeric Decay. Phys. Rev. Lett 125 (19): 192505; doi: 10.1103/PhysRevLett.125.192505
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