Scientists have built the world's first nuclear clocks; devices that, they say, could help open up some of the most fundamental questions in physics. These two instruments are the latest generation of atomic clocks that measure time by observing the light resulting from transitions that occur within the atomic nucleus and among protons and neutrons.
Atomic clocks have been used for years to maintain precise timekeeping and the first example was built in 1949; however, despite their name they do not use nuclear fusion or fission.
Until now the most precise clocks in the world relied on electron transitions between energy levels in atoms, but this discovery has shown that the reference of a clock can be taken directly from the atomic nucleus itself.
Research teams at Tsinghua University in China and other institutions in that country and also at TU Wien in Austria, each separately, on Wednesday published reports of their achievements in two papers in the journal Nature (source in English).
This clock uses thorium-229; a rare atom whose nucleus can be switched between energy states using ultraviolet light produced by a laser. So far it is the only known nucleus that behaves in this way.
Members of the team built a laser that produces ultraviolet light with a wavelength of 148.4 nanometres and aimed it at small calcium fluoride crystals containing thorium-229.
The main result was that the nuclear clocks worked; the laser locked onto the thorium-229 nucleus and measured time stably and during the test period reached a precision at the level of one in a million billion (10⁻¹⁵).
Although precise timekeeping is vital for everyday technologies such as satellite navigation and communications, nuclear clocks could make these systems even more accurate.
The paper states that these new clocks could also be important in the field of fundamental physics, although their exact uses have not yet been determined.