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 made of quarks. They are usually spherical in shape, but when we remove particles from inside them, they don’t necessarily just shrink and retain their shape. We know from the research conducted so far that mercury and bismuth nuclei, deprived of even a single neutron, can dramatically change their shape from that resembling a standard football to that of a rugby ball.
Scientists from ISOLDE decided to investigate how the shape of a gold atom deprived of neutrons changes. So they looked at gold atoms with between 104 and 97 neutrons. A stable natural gold atom has 118 neutrons and 79 protons.
The research results were surprising. Even with 108 neutrons, the gold atom was a sphere. At 107 it changed shape to that of a rugby ball and remained so until 101 neutrons in the nucleus. Also in the case of gold – as before in the case of mercury, bismuth and lead – there was a change in the average radius of a square atom of approximately 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 core shape evolution before. Unlike mercury and bismuth, where the changes are evenly distributed to reduce bond energy, 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 the study’s lead author, James Cubiss.
Changes in the mean square radius of mercury, bismuth, lead and gold atoms about 104 neutrons-
After the research, theoreticians 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 the changes in the shape of the gold atom only if they introduced additional data into the calculations.
So, 50 years after the discovery of the phenomenon of changing the shape of the nucleus of an atom, this phenomenon is still a mystery to physics.