From Atomic to Nuclear Clocks: Harnessing the Potential of Scandium as a More Accurate Timekeeper

The concept of time is a fundamental aspect of human existence and plays a critical role in living an organized and structured life. Throughout the history of mankind, several tools have been developed to measure time. In a recent study, an international research team has made a groundbreaking discovery that can lead to the development of a more accurate type of clock.

Atomic Clock Mechanism

For thousands of years, the Earth's rotation was the reference for timekeeping, but its accuracy is limited to only one millisecond per day. In 1948 the first atomic clock was invented and has since been used as the standard for measuring time.

Most atomic clocks are based on oscillators such as cesium, which can oscillate at very reliable frequencies upon excitation by microwave radiation. These clocks use electrons in the atomic shell of cesium as pulse generators. The electrons can be raised to a higher energy level using microwaves of a known frequency.

As microwaves are bombarded with cesium atoms, the frequency of the radiation is regulated such that the absorption of the microwaves is maximized. Experts refer to this process as resonance. The oscillator used in generating microwaves can be kept so stable with the help of resonance that atomic clocks will be accurate to within one second within 300 million years.

However, the accuracy of an atomic clock is dependent on the width of the resonance used. Conventional cesium atomic clocks use a very narrow resonance, while strontium atomic clocks achieve a higher accuracy with only one second in 15 billion years. It is impossible to achieve further improvement beyond this accuracy level using the electron excitation method.

Future of Timekeeping

Scientists worldwide have been working on a nuclear clock that uses transitions in the atomic nucleus as the pulse generator rather than in the atomic energy level for several years. Although nuclear resonances are much harder to excite, they are much more accurate than the resonances of electrons in the shell of an atom.

At the European X-ray free-electron laser (XFEL) facility, an international research team has taken a step toward a new generation of accurate clocks. They created a much more precise pulse generator that uses the element scandium. Scandium is readily available as a high-purity metal foil or as a component of the compound scandium dioxide.

Their experiment irradiated a 0.025-millimeter-thick scandium foil with X-ray laser light. The excited atomic nuclei emitted a characteristic afterglow, indicating scandium's narrow resonance line.

This element's atomic resonance requires X-rays with an energy of 12.4 kiloelectronvolts (keV) and has a width of only 1.4 femtoelectronvolts (feV). This measurement is 1.4 quadrillionths of an electronvolt, only about one-tenth of a trillionths of the excitation energy. In short, the accuracy of the scandium nuclear clock is 1:10,000,000,000,000 possible.

This corresponds to one second in 300 billion years, according to DESY researcher Ralf Röhlsberger. It means if a regular watch loses a second a year, it will be 9,512 years slow when a scandium-based nuclear clock is a second out.