Making the Impossible Possible: Nuclear Physicists Create An Exceptionally Neutron-Rich Sodium Isotope

At RIKEN, nuclear physicists have accomplished what was once thought to be unachievable. They have managed to generate a remarkably neutron-dense isotope of sodium, 39Na, a form of the element that previous atomic nuclei models deemed improbable. This advancement carries critical implications for our comprehension of atomic nuclei structure and the astrophysical procedures leading to the formation of heavier elements on Earth.

By establishing this extremely neutron-rich sodium isotope, the physicists have unveiled another layer of the intricate universe of nuclei. The existence of this 39Na form, which many believed couldn’t be created, has been confirmed for the first time by the team at RIKEN.

Interestingly, if this unusually heavy sodium version were combined with the most neutron-rich chlorine isotope to make table salt, it would still taste and function like regular salt, although it would be about 1.6 times heavier, explains nuclear physicist Toshiyuki Kubo.

However, the significance of this finding extends far beyond its novelty. It holds paramount importance for the understanding of atomic nuclei structure theories. It also sheds light on the astrophysical procedures that yield Earth’s heavier elements.

As per Kubo, this discovery serves as an essential benchmark for improving neutron-rich nuclei models and assessing their precision. Theoretical examinations of such nuclei entail complicated computations, and until now, theoretical physicists could only precisely model more stable nuclei with fewer neutrons. This new finding could help refine calculations for more neutron-rich nuclei.

This advancement also carries significant implications for our understanding of the origins of heavier elements. For instance, the nuclear astrophysical processes that create Earth’s heavy metals are believed to be driven by the enormous energy produced during the fusion of two neutron stars or collisions between neutron stars and black holes. The resulting gas and dust contribute to the rare materials found on planets like Earth, but the exact mechanisms for the production of heavy metals have been a long-standing matter of debate.

When it comes to sodium, each of the 118 known elements carries a fixed number of protons (11 for sodium), but the number of neutrons in its nuclei can vary, notes Kubo. The stable form of sodium contains 12 neutrons, while the recently discovered one packs a whopping 28, which is two more than the previous record-holder for the most neutron-rich sodium isotope, 37Na, discovered over two decades ago.

Kubo’s team initiated the search for this new sodium form, called 39Na, following an unexpected finding in a previous experiment. They were astounded to detect what seemed to be one nucleus of 39Na. In their latest experiment, they conclusively demonstrated the existence of 39Na by creating nine nuclei of the isotope during a two-day trial run at RIKEN’s Radioactive Isotope Beam Factory.

Kubo has a long track record of participating in the creation of new isotopes during his four-decade career, contributing to the discovery of roughly 200 new isotopes. The achievement of establishing 39Na holds special significance, especially since many nuclear models suggested it shouldn’t exist.

The discovery of 39Na presents a challenge to ascertain the ‘drip line,’ the boundary determining the maximum number of neutrons an element can have before it begins to leak neutrons. This boundary not only provides a crucial benchmark to nuclear theories but also plays a pivotal role in nucleosynthesis theories.

However, defining the drip line for an element is a formidable task. So far, nuclear physicists have only succeeded in determining it for neon, the tenth element in the periodic table, leaving 108 more elements to investigate.

Related links:

• RIKEN’s Official Website
• Article on the Discovery of 39Na in Physical Review Letters
• Article on Nuclear Shape Impact on Neutron Dripline in Nature