Notes on the Lecture: The Future of the Periodic Table

Introduction

• Thanks to Raycon for supporting PBS.
• Discussion on the extension of the periodic table and the discovery of new elements.
• Current elements at the end of the table are unstable and decay quickly.
• Question: Have we reached the end of discoverable elements?

The Island of Stability

• New rows in the periodic table remain unexplored.
• The concept of the "island of stability": a region where new heavy elements may exhibit unusual stability.
• Existing methods of creating these elements through particle accelerators are inadequate.
• Astrophysicists propose that neutron star mergers may create elements in this stable region.

Understanding Nuclear Instability

• Nuclear Stability: Nuclei are held together by the strong nuclear force and affected by the repulsive Coulomb force between protons.
  • Neutrons are crucial in preventing repulsion among protons.
  • Stable isotopes often have proton and neutron numbers that are equal or close.
  • Examples:
    • Helium-4: 2 protons, 2 neutrons
    • Carbon-12: 6 protons, 6 neutrons
    • Lead-208: 82 protons, 126 neutrons (doubly magic)
• Decay Mechanisms:
  • Most elements beyond lead-208 are radioactive, decaying via:
    • Alpha particles (He-4 nuclei)
    • Beta particles (electrons from neutron decay)
• The heaviest stable element is lead-208; beyond this, nuclei become too unstable.

Creating New Heavy Elements

• Current methods involve colliding smaller nuclei to create super-heavy elements.
• Example: Oganesson (element 118) created by smashing calcium with californium.
• Recent advances using titanium-50 at Berkeley Lab aim to discover element 120.
• New elements produced are expected to be extremely unstable due to insufficient neutrons.
• Theoretical island of stability exists between atomic numbers 110 to 114, requiring a neutron-to-proton ratio of about 1.5.

Neutron Star Mergers and Heavy Elements

• Neutron Stars: City-sized nuclei with star-like masses formed from the collapse of massive stars.
• Neutron star mergers are thought to produce heavy elements through rapid neutron capture (R-process).
• These events send neutron-rich material into space, potentially creating elements in the island of stability.
• Observations:
  • First recorded neutron star merger (GW170817) in 2017, confirmed as a kilonova.

Evidence of Heavy Element Production

• Heavy elements (transuranics) produced from neutron star mergers display specific signatures in stellar spectra.
• No direct detection of super-heavy elements yet, but evidence found in the decay products of these elements.
• Kilonova emissions may display detectable brightness changes caused by the decay of island of stability elements.

Future Prospects

• The possibility of proving the existence of island of stability elements lies in future neutron star observations.
• Key to successful detection includes catching kilonovae shortly after they occur.
• Collaboration between astrophysics and nuclear physics may yield new discoveries in element synthesis.

Conclusion

• Future observations and experiments may lead to the discovery of new elements and support the existence of the island of stability.