Israeli and German scientists have decided to use thorium-229 to develop an ultra-precise nuclear clock, capable of detecting forces 10 trillion times weaker than gravity.
Such sensitivity could make this clock an ideal tool for detecting dark matter. For more than 100 years, physicists have been trying to uncover the nature of mysterious dark matter, which is believed to make up up to 80% of the Universe. Scientists have explored a large number of ways to detect it — from attempts to create dark matter particles in accelerators to searches for weak cosmic radiation. However, the key characteristics of this mysterious substance still remain unexplored.
Although dark matter does not interact with light, it is believed, to have a subtle effect on ordinary matter, but modern instruments are unable to detect this ultra-fine interaction. According to experts, the creation of an ultra-precise nuclear clock may finally allow the detection of dark matter.
This clock will be so accurate that even minor deviations in its movement could indicate the presence of dark matter. The device will measure time based on the vibrations of the atomic nucleus. Last year, research teams from Germany and Colorado took an important step forward by using the radioactive isotope thorium-229 in the early stages of creating such a clock.
After Israeli researchers from the theoretical physics group of Prof. Gilad Perez at the Weizmann Institute got acquainted with the success of their american and german colleagues, they decided to make their own contribution to the creation of this device and the search for dark matter. Together with German scientists, they published a study on how dark matter can affect and subtly change the properties of the thorium-229 nucleus.
Just as rocking a child on a swing requires the right moment to support smooth and uniform motion, the atomic nucleus also has an optimal oscillation frequency called the resonance frequency. Radiation at this frequency can cause the nucleus to oscillate like a pendulum between two quantum states — the ground state and the high-energy state.
Most materials have a high resonance frequency and require powerful radiation to excite the nucleus. In 1976, however, scientists discovered that thorium-229, a byproduct of the U.S. nuclear program, was a unique exception.
Its natural resonance frequency is low enough to be controlled by lasers using relatively weak ultraviolet radiation. This makes thorium-229 a promising candidate for use in an innovative nuclear clock, in which time would be measured by oscillating the atom’s nucleus between quantum states.
“A nuclear clock could be an ideal detector capable of picking up forces 10 trillion times weaker than gravity and having a resolution 100,000 times higher than current methods of searching for dark matter”, — the authors of the study emphasize.
However, progress stopped literally at the very first stage, when scientists tried to measure the resonant frequency of thorium-229 with maximum accuracy. To determine the resonant frequency of a nucleus, physicists irradiate it with a laser at different frequencies and observe, how much energy the nucleus absorbs and emits during the transition between quantum states.
For almost 50 years, scientists have been unable to measure resonance frequency of thorium-229 with sufficient accuracy to create a nuclear clock, but last year two important discoveries were made at once. First, a group from the German National Institute for Metrology (PTB) published relatively accurate measurements. A few months later, a group from the University of Colorado published results, that were several million times more accurate. Theoretical calculations led by Dr. Wolfram Ratzinger of Perez’s group showed, that the new measurements can detect the influence of dark matter, even if it is 100 million times weaker than gravity.
“We still need even greater precision to develop nuclear clocks. But we have already found an opportunity to study dark matter. In a universe consisting only of visible matter, the physical conditions and absorption spectrum of any material would remain unchanged. But as dark matter surrounds us, its wave nature can subtly change the mass of atomic nuclei and cause temporary shifts in their absorption spectrum. We hypothesized, that the ability to detect the smallest deviations in the thorium-229, absorption spectrum with high accuracy could reveal the influence of dark matter and help us study its properties”, — explains Gilad Perez, team leader of the Israeli researchers.
According to Ratzinger, this is an area where no one has ever searched for dark matter. According to him, the calculations show that the search for landslides alone resonant frequency is not enough. Ratzinger argues, that in order to detect the influence of dark matter, it is necessary to detect changes across the entire absorption spectrum.
The results of the study are published in the journal Physical Review
Source: SciTechDaily
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