- An isotope of gold has given scientists their first glimpse of longitudinal nuclear wobbling.
- The documented wobbling is similar to the way the Earth wobbles, caused by things like unequal axes.
- The nucleus is a prolate spheroid, like a rugby ball, and should lead to discovery of more wobbly isotopes.
Scientists have identified a short-lived isotope of gold with a wobbly nucleus. The isotope is created by a nuclear reaction, and the research team believes the nucleus wobbles because of one extra nucleon. A large team from the U.S. and India has published its findings in Physical Review Letters.
The University of North Carolina released a Q&A with research team member Robert Janssens. “Gold 187 has an odd number of nucleons and that's important,” he says, because protons and neutrons “like to go two-by-two” most of the time. Plenty of nuclei have odd numbers of nucleons overall, but this gold isotope is a rare one because of the wobbling.
This specific wobbling dynamic is called longitudinal wobbling, “in which the nucleon’s orbital axis aligns with the nucleus’s intermediate-length axis.” The other form of wobbling, called transverse wobbling, results from “[a]lignment between the nucleon’s orbital axis and the nucleus’s long or short dimensions” and has been seen several times before. This experiment is the first ever observation of longitudinal wobble.
One of the team’s goals was, of course, to observe the wobble directly—it was first predicted in 2014, but took until now to be seen and measured. “The researchers spotted the new mode’s signature in the nuclear debris created by firing fluorine ions at an ytterbium target,” Physics explains. “By analyzing the gamma rays emitted as these excited states decayed, the team reconstructed the initial population—including the predicted longitudinal wobbling states.”
But they also wanted to understand if the wobble is a total fluke or if it represents, as with transverse wobble, a group of nuclei that will behave the same way. “Studying this particular gold isotope we found that it is triaxial, meaning [it] has three axes of different length, and there are not that many nuclei that are triaxial,” Janssens says. The researchers “expect further examples of heavy triaxial nuclei to show up in future studies,” Physics reports.
Many people think Earth is a sphere and, if they’ve ever thought about it at all, that it rotates smoothly. But Earth is an oblate spheroid, meaning a 3D shape created by an ellipsis that’s rotating around its shorter axis—like a more rounded jelly donut. And Earth wobbles in its rotation. The gold isotope’s nucleus exhibits the same behavior, but instead of oblate, its nucleus is prolate. It rotates around the longer axis, like a spiraling football.
But the wobbling is the same, and identifying and observing it is big news, from the nano scale all the way up. “And with that, we could demonstrate that in the same way Earth wobbles around one of its axes, this gold wobbles around its longest axis,” Janssens says. The ramifications could be huge. “We'd like to know if nuclei are as universal as we'd like to think, and studying these basics shows us nuclear forces we don't understand or that we haven't seen before.”
You Might Also Like