Changes in the shape of the gold nucleus surprised physicists and showed how little we know

As mass is lost, atomic nuclei tend to shrink. However, it is important to remember that they are complex systems, made of protons and neutrons, which in turn are composed of quarks. They are usually spherical in shape, but when we remove the particles from inside them, they do not necessarily shrink and retain their shape. We know from research to date that mercury and bismuth nuclei, deprived of even a single neutron, can change their shape dramatically from that of a standard football to that of a rugby ball.

Scientists from ISOLDE decided to investigate how a neutron-free gold atom changes shape. So they looked at gold atoms that contained between 104 and 97 neutrons. A stable natural gold atom contains 118 neutrons and 79 protons.

The research results were surprising. Even with 108 neutrons, the gold atom was a sphere. At 107, its shape changed to the shape of a rugby ball and remained that way until 101 neutrons in the nucleus. In the case of gold as well – as in the case of mercury, bismuth, and lead – there was a change in the average radius of the square atom by about 104 neutrons. However, in the case of gold, there was an additional shape change that occurred at 99 neutrons.

-We have never observed such a pattern of basic shape evolution before. Unlike mercury and bismuth, where the changes are evenly distributed to minimize the energy of the bonds, in the case of gold, the rugby ball shape clearly wins when there are about 104 neutrons in the nucleus. Later, at 99 neutrons, the gold nucleus looks like a rugby ball again and suddenly turns into a standard ball, says lead author researchJames Kubis.

After the research, theorists got to work and tried to explain the observed phenomenon on the basis of existing theories. They found that the model of the structure of the atomic nucleus they used correctly reflected changes in the shape of the gold atom only if they included additional data in the calculations.

So, 50 years after the discovery of the phenomenon of changing the shape of the atomic nucleus, this phenomenon remains a mysterious mystery in physics.