Nuclear physicists at RIKEN have efficiently created a particularly neutron-rich isotope of sodium, 39Na, beforehand predicted by many atomic nuclei fashions to be non-existent. This discovery has vital implications for our understanding of atomic nuclei construction and the astrophysical processes that kind heavier components on Earth.
Nuclear physicists have made essentially the most neutron-rich type of sodium but, which is able to assist reveal extra in regards to the complicated world of nuclei.
Physicists at RIKEN have created an exceptionally neutron-rich sodium isotope, 39Na, which was beforehand believed to be not possible. This breakthrough has main implications for understanding atomic nuclei construction and the creation of Earth’s heavier components.
In extraordinarily neutron-rich type of the ingredient sodium—which many fashions of atomic nuclei predict shouldn’t exist—has been created by nuclear physicists at RIKEN for the primary time[1].
If you made desk salt from this super-heavy model of sodium—and essentially the most neutron-rich isotope of chlorine, salt’s different constituent—it will style and behave like regular salt, besides it will be roughly 1.6 occasions heavier, says nuclear physicist Toshiyuki Kubo.
But way over being a scientific curiosity, this discovering has essential implications for theories on the construction of atomic nuclei. This information in flip informs our understanding of the astrophysical processes that kind Earth’s heavier components.
In phrases of nuclear concept, the discovering offers a significant reference level for tweaking fashions of neutron-rich nuclei and for assessing their accuracy, explains Kubo. Theoretical studies of neutron-rich nuclei involve extremely complicated calculations, and theoretical physicists have so far only been able to precisely model more stable nuclei with few neutrons. This finding could help refine calculations for nuclei with more neutrons.
This in turn has implications for our understanding about the origins of heavier elements. For example, the nuclear astrophysical processes that create Earth’s heavy metals are thought to be the result of the huge amounts of energy produced by the merger of two neutron stars or collisions of neutron stars and black holes. The gas and dust released eventually contribute to the rare materials of planets, such as Earth. However, the exact processes that produce heavy metals have long been debated.
A new square on the drip line: Each square indicates an isotope, with the number of protons increasing as the squares move vertically upward and the number of neutrons increases horizontally to the right. The known existence limit, the neutron ‘drip line’, is indicated by a thick blue line. Sodium-39 (39Na) in red has 11 protons and 28 neutrons, giving it a mass number of 39. Its recent discovery by RIKEN researchers has seen it added to the drip line. Credit: © 2023 RIKEN
Packing neutrons into sodium
Each of the 118 known elements has a fixed number of protons (11 in the case of sodium), but the number of neutrons in its nuclei has can vary, notes Kubo. The only stable form of sodium contains 12 neutrons, whereas the newly discovered one has more than double at 28, which is two more neutrons than the previous record holder for the most-neutron-rich isotope of sodium, 37Na, which was discovered more than 20 years ago.
Since neutrons are electrically neutral, they don’t influence an atom’s electrons and hence have no effect on the element’s chemistry. Thus, atoms of the same element that contain different numbers of neutrons—known as isotopes—are chemically indistinguishable.
The impetus to search for the new form of sodium (called 39Na because its nucleus contains 39 neutrons and protons) came from a previous experiment, when a team led by Kubo at the RIKEN Nishina Center for Accelerator-Based Science stumbled upon what appeared to be one nucleus of 39Na. “We were very surprised at this one event,” recalls Kubo. “And so, we decided to revisit the search for 39Na in our present experiment.”
In the latest experiment, they put the existence of 39Na beyond all doubt by creating nine nuclei of the isotope in a two-day run at RIKEN’s Radioactive Isotope Beam Factory—one of only about three nuclear facilities in the world currently capable of producing such nuclei.
Isotope hunter
It’s far from the first time that Kubo has helped to create a new isotope during his four-decade-long career. “Actually, I’ve been involved in discoveries of about 200 new isotopes or so,” he says. “I really enjoy creating and observing what nobody has ever seen before.”
But the discovery of 39Na, has special significance for him, not least because many nuclear models predict that it shouldn’t exist. “The discovery makes a significant impact on nuclear mass models and nuclear theories that address the edge of the nuclear stability, because it provides a key benchmark for their validation,” explains Kubo. For example, Kubo notes that a model developed by a Japanese team in 2020 correctly predicted the existence of 39Na and its predictions for other isotopes have been on target[2], boosting its credibility.
Tracking the drip line
One motive the invention is essential is as a result of 39Na might properly be essentially the most neutron-rich model of sodium that it’s attainable to provide. Nuclear physicists are notably fascinated with figuring out the utmost variety of neutrons a component can have earlier than it begins leaking neutrons—a amount often called the neutron drip line when plotted on a desk of nuclei. The location of this restrict offers a key benchmark to not solely nuclear theories, but in addition nuclear mass fashions that play a key position in theories of nucleosynthesis.
But this can be very troublesome to establish the drip line for a component—nuclear physicists have to this point solely succeeded in figuring out it as much as the tenth ingredient within the periodic desk, neon, which implies they nonetheless have 108 extra components to go.
One motive why it’s laborious to measure the dripline is due to the tiny potentialities concerned in creating nuclei that lie near limits of stability. Another issue is that this can be very difficult to rule out the existence of different nuclei which have much more neutrons. Kubo says that it might be attainable to make 41Na, by which case it will turn into the dripline for sodium, though he notes that the 2020 Japanese mannequin predicts that 39Na is the drip line.
Next Kubo and his workforce intend to try to experimentally decide the dripline for magnesium—one ingredient up from sodium. They additionally wish to probe the construction of 39Na. “We would like to directly study the nuclear structure that allows 39Na to exist,” Kubo explains.
References:
- “Discovery of 39Na” by D. S. Ahn et al., 14 November 2022, Physical Review Letters.
DOI: 10.1103/PhysRevLett.129.212502 - “The impact of nuclear shape on the emergence of the neutron dripline” by Naofumi Tsunoda, Takaharu Otsuka, Kazuo Takayanagi, Noritaka Shimizu, Toshio Suzuki, Yutaka Utsuno, Sota Yoshida and Hideki Ueno, 4 November 2020, Nature.
DOI: 10.1038/s41586-020-2848-x
