new superheavy isotope nuclear stability

New Superheavy Isotope ²⁵⁷Sg Sheds Light on Nuclear Stability and K-Isomers

Unveiling ²⁵⁷Sg: A New Window into Nuclear Stability

A recent publication in Physical Review Letters details the discovery of a new superheavy isotope, ²⁵⁷Sg (seaborgium), by researchers at GSI Helmholtzzentrum, offering fresh perspectives on the nuclear stability and fission behaviour of the heaviest elements.

Superheavy elements occupy a finely tuned equilibrium between the nuclear force binding protons and neutrons and the electromagnetic force driving protons apart.

Were it not for quantum shell effects—akin to electron shells in atoms—these colossal nuclei would disintegrate in under a trillionth of a second.

Publisher website interviewed Dr. Pavol Mosat and Dr. J. Khuyagbaatar, co-authors of the study from GSI Helmholtzzentrum für Schwerionenforschung in Germany, regarding their research.

The findings highlight gaps in our understanding of extreme atomic nuclei, hinting that the quantum forces preventing their rapid disintegration may function in unexpected ways.

Exploring the Nature of Nuclear Stability

Synthesis of ²⁵⁷Sg Using Fusion Reactions

To create the isotope ²⁵⁷Sg, the international team utilized fusion reactions between chromium-52 and lead-206 within GSIs TASCA recoil separator.

The researchers discovered that the new isotope survives for 12.6 milliseconds—outlasting its even-even neighbour, ²⁵⁸Sg—and decays via both spontaneous fission and alpha emission.

Alpha Decay and Fission of Daughter Isotopes

The alpha decay route offered especially valuable insights. Following alpha emission, ²⁵⁷Sg becomes ²⁵³Rf (rutherfordium), which proceeds to fission in a mere 11 microseconds.

This observation aligns with recent studies that have cast doubt on the conventional view of angular momentum's role in fission. Although it was long thought that higher K quantum numbers would strongly hinder fission, new data point to a more intricate relationship.

"We examined the isotopes ²⁵⁷Sg and ²⁵³Rf and observed that K-quantum numbers generally impede fission," Mosat explained. "That said, the precise degree of this hindrance remains undermined."

Discovery of the First K-Isomer in Seaborgium

Arguably of even greater importance was the team's identification of the first K-isomeric state in a seaborgium isotope. These K-isomers are unusual nuclear arrangements with elevated angular momentum that exhibit a marked resistance to fission compared to typical nuclear states.

In the case of ²⁵⁹Sg, the researchers observed a conversion electron signal emerging 40 microseconds after the nucleus formed—clear evidence of a K-isomeric state potentially hundreds of times more stable against fission than the ground state.

"K-isomeric states have previously been observed in superheavy elements like ²⁵²⁻²⁵⁷Rf and ²⁷⁰Ds," remarked Khuyagbaatar. "However, this marks the first time such a state has been identified exclusively in isotopes of seaborgium, which contain 106 protons."

This discovery addresses a significant gap in our understanding of superheavy elements and may prove pivotal in guiding future element searches.

Towards Understanding the 'Island of Stability'

The discovery arrives at a pivotal moment for research into superheavy elements.

Scientists have long pursued the so-called "Island of Stability"—a hypothetical region where superheavy nuclei might enjoy extended lifetimes thanks to favourable shell structures. Yet the latest findings imply that this picture may be more intricate than previously believed.

"It is possible that a superheavy nucleus—say, an isotope of an as-yet-undiscovered element—may survive for less than a microsecond," said Khuyagbaatar.

In such a scenario, the path to discovering element 120 could be fraught with complications in terms of separation and detection. Nonetheless, the existence of a K-isomer in this nucleus might extend its longevity, as seen in our recent finding with ²⁵²Rf.

The researchers believe that the as-yet-undiscovered ²⁵⁶Sg may possess a half-life far shorter than current models predict —possibly falling from six microseconds to merely one nanosecond.

Such a marked difference in nuclear stability would offer a valuable new perspective within the field of nuclear physics.

Barriers to Implementation and Next Steps

Challenges in Detecting Millisecond-Lived Nuclei

Achieving this result entailed surmounting considerable technical hurdles. Detecting nuclei with lifespans of only milliseconds required exceptionally rapid systems and finely tuned timing.

"For short-lived nuclei, it is essential to employ a compact separator and more importantly, rapid digital electronics capable of resolving decay signals to around 100 nanoseconds," said Khuyagbaatar.

Future Plans for ²⁵⁶Sg and K-Isomeric States

The team at GSI developed bespoke digital electronics that have played a vital role in several superheavy element discoveries.

The researchers now aim to synthesize ²⁵⁶Sg in order to determine whether the anticipated sharp decline in stability truly manifests.

"Indeed, we intend to pursue further investigations into long-lived K-isomeric states in superheavy nuclei," Mosat stated. "Our immediate objective is to attempt the synthesis of the next unknown isotope, ²⁵⁶Sg."

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