![]() ![]() According to the paper, it should be possible to excite the nucleus of thorium-229 using ultraviolet light, a far more manageable energy requirement and similar lasers are already used in laser-based atomic clocks today. Yet according to a paper published today in Nature, a team of researchers at Physikalisch-Technische Bundesanstalt (PTB) in Germany may have found an exception to this rule. This high energy requirement was thought to make atomic clocks based on nuclear transitions infeasible. Whereas electrons in cesium-133 can be bumped to a higher energy state at a frequency of approximately 9.1 gigahertz (on the low end of the microwave range of the electromagnetic spectrum), exciting an atom’s nucleus requires energy in the x-ray range, where frequencies range from 30 petahertz to 30 exahertz (read: 30 quadrillion to 30 quintillion cycles per second). The difficulty with nuclear excitations, however, is that they require much higher energy levels than electron energy transitions because their protons and neutrons are more densely packed. The advantage of using a nucleus is that its energy transitions occur at much higher frequencies than electron transitions, which would allow for even more precise measurements of time. Nevertheless, physicists have wondered if still more precise atomic clocks were possible by using a transition frequency in the nucleus of an atom, rather than in its electrons. This method of keeping time with atomic clocks has been refined over the last fifty years to the point that the most accurate clock in the world will only deviate by a second over 200 million years, but the basic principles have remained the same. ![]() In this analogy, microwave energy sets the pendulum in motion and every 9,192,631,770 swings is marked as one second on the clock face). (Another way to think about this is that the cesium atom is a clock and the electron is its pendulum. When cesium-133 atoms are hit with microwaves at this frequency, it causes the atom’s single outermost electron to transition between energy states at the same rate, and it is this rapid transition that was used to formally define the length of a second in 1967. In the case of cesium-133, that wavelength is about 3.2 cm, which means the wave oscillates at a frequency of 9,192,631,770 cycles per second. Different types of atoms are able to absorb energy at different wavelengths. These orbits can be changed by adding energy to the system, which causes the electrons to temporarily get bumped up to a higher energy level and emit electromagnetic radiation during the transition. It worked by exposing cesium-133 atoms in a vacuum to microwave energy and then measuring how well the atom absorbs this microwave radiation.Įlectrons orbit the nucleus of an atom at certain stable energy levels that depend on the electrical properties of the nucleus itself. In 1955, English physicists Louis Essen and Jack Parry built the first accurate atomic clock at the National Physical Laboratory in the UK. In a new paper published today in Nature, researchers in Germany describe experiments that showed for the first time what this clock would actually look like, a major milestone into making a nuclear clock a reality. Since protons and neutrons are densely packed in the nucleus and are thus less likely to be disturbed by outside influences, researchers think the nucleus could serve as the basis for an ultra-precise atomic clock in the future. But now researchers around the world are working on building a better model based not on the electrons of an atom, but the nucleus. Indeed, the most accurate clock in the world, which is run by the National Institute of Standards and Technology in Colorado, is a ytterbium atomic clock. Since they were first created in the mid-twentieth century, atomic clocks have been the gold standard of timekeeping.
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