It is the most accurate machine. Clocks based on the energetic oscillations of cesium atoms move forward or backward one second every 300 million years. Such accuracy is necessary for GPS positioning, official watch synchronization, and some scientific research.
The most common atomic clocks use atoms of cesium 133 , an isotope of cesium (that is, it has the same protons in its nucleus as it, but different numbers of neutrons). Simplifying a lot: what these devices do is alter the energy states of the cesium atoms by means of a microwave bombardment and calculate the time that these energy changes last. This process is repeated with microwaves emitted at different frequencies.
The frequency that alters the state of greater number of atoms and maximizes its absorption of radiation and its subsequent emission of photons (that is, its energy changes) is considered the natural resonance frequency of the cesium atom, and is used to define the second.
Thus, this is equivalent to 9,192,631,770 cycles of an atom of the isotope cesium 133. Each cycle corresponds to a change in atomic energy. The high number of cycles that are detected in one second gives an idea of the extreme precision of the measurement and explains why atomic clocks are essential for technologies that require maximum accuracy, such as GPS and those related to astronomical measurements.
NASA’s deep space atomic clock, seen here in an artist’s illustration, will test new technologies for deep space navigation. / Credit: NASA
An atomic clock in space
On June 24, 2019, NASA launched a new atomic clock into orbit on a Falcon Heavy. The Deep Space Atomic Clock, developed by NASA’s Jet Propulsion Laboratory, is an upgrade for the atomic clocks we use here on Earth and for clocks that already fly on satellites such as those that provide GPS, as published the Live Science web.
This new atomic clock will make the spacecraft’s navigation to distant objects in space, for example on the trip to Mars, more autonomous. The precision in the measurement of the position of the spacecraft that scientists hope to obtain with it will allow spacecraft traveling in deep space to act on their own, without much communication with Earth. It would be a great improvement to the way the spacecraft is currently navigated, NASA explained in a statement.
These clocks use different elements: cesium, strontium, hydrogen, aluminum, mercury … Those of cesium and strontium are the most accurate. Three are in Colorado (USA). On Earth, there are hundreds of these devices in operation, and their measurements have allowed the creation of the international atomic time standard (TAI), used throughout the world.
How they work
Take for example a cesium atomic clock, which is a structure with a vacuum tube and composed of different elements. It all starts with a source of these atoms, which are found in different energy levels.
– Laser A : cesium atoms pass through a laser that minimizes their energy levels.
– In the microwave chamber, microwave radiation is emitted at the right frequency so that the entering atoms reach an excited state of energy.
– Crossover reduces high microwave frequencies (over 9 billion cycles per second) for easy counting.
– Magnets : There are two magnets on each side of the microwave chamber. The former ensures that only low-energy atoms enter it. The second sends the atoms recharged by the impact of the microwaves to the detector.
– The servomechanism changes the frequency of the microwaves in the chamber to put as many cesium atoms as possible in the excited state, in such a way as to increase the intensity of the light signal.
– Laser B: A second laser causes the atoms in the excited state of energy to emit light.
– Detector : The detector, located at the end of the vacuum tube, captures the photons emitted by the excited atoms.
The first atomic clock in history
In 1949 the first atomic clock in history was built. It was designed by Harold Lyons for the US National Institute of Patterns and Technology (NIST). These types of watches are capable of measuring time in attoseconds, that is, in the trillionth of a second.
