Counting Electrons Reveals Thorium’s Nuclear Tick in Solid Clock

Syllabus: GS3/Science and Technology

Context

• Scientists have found a way to detect thorium-229’s nuclear ‘tick’ in a solid, opening a path to miniaturised nuclear clocks.

About

• Conventional atomic clocks count electron transitions, which are sensitive to external disturbances (electric/magnetic fields).
  • Nuclear energy levels are far more shielded, promising more stable timekeeping.
• Why Thorium-229 (²²⁹Th)?
  • It has a uniquely low-energy nuclear excited state which can be directly excited using vacuum-ultraviolet (VUV) lasers—a rare and crucial property.
• Main experimental challenge: In solid materials, the excited nucleus usually relaxes via internal conversion (energy transferred to an electron) instead of emitting a detectable photon, making direct detection difficult.
• New breakthrough approach: Instead of avoiding internal conversion, researchers used it as the signal by embedding ²²⁹Th in thorium dioxide (ThO₂), exciting nuclei with VUV laser pulses and detecting the delayed electrons emitted during nuclear decay.
• Key Results:
  • Clear nuclear resonance detected at 2,020,407.5 GHz.
  • Internal conversion lifetime measured at 12.3 μs.
  • Implies a nuclear clock accuracy of 1 second error in ~15.8 billion years.
• Significance: 
  • Opens new materials and designs for nuclear clocks.
  • Enables miniaturisation, since time can be read via electron current rather than complex optics.
  • Potential applications in fundamental physics, precision sensing, and tests of physical constants.

Nuclear Clock

• A nuclear clock works by using ultraviolet light to excite the nucleus of a special atom, like thorium-229. 
• When the light hits the nucleus at just the right frequency, it causes the nucleus to change its energy state, like flipping a tiny switch. 
• By precisely measuring and counting these energy flips, scientists can create an extremely accurate timekeeping device.

Difference Between Atomic Clock and Nuclear Clock

Key Advantages of Nuclear Clock over Atomic Clock

• Much greater accuracy and stability.
• Better for testing fundamental constants.
• Less environmental interference.
• Higher sensitivity to gravitational time dilation.

Source: TH