Evrim Yazgin
Cosmos science journalist
Physicists at the University of Queensland (UQ) in Australia have found a way to use muonic atoms to better understand the magnetic structure of the nucleus.
Science has known about atoms for about 200 years when English chemist John Daltan developed the modern theory of atoms. In fact, the concept of atoms is much older – dating to the ancient Greek philosopher Democritus in around 400 BCE.
You might remember your school science classes when you were told about the atomic nucleus made of protons and neutrons, and the orbiting electrons.
So, you’d imagine that physics has explored everything there is to explore in atoms. Not so.
A growing area of research is the examination of “exotic atoms” – atoms where one or more of the subatomic particles within the atom is replaced with another type of particle.
Muonic atoms are one type of exotic atom. In these atoms, the orbiting, negatively-charged electrons are replaced by muons.
Muons are like electrons in almost every way. They are both fundamental particles which appear in the standard model of particle physics, belonging to the group called leptons. They both have a charge of -1.
The main difference is that muons are 207 times heavier than electrons.
The new UQ-led research, published in the Physical Review Letters, combines theory and experiments to show that muonic atoms are as hard a nut to crack as previously thought. In fact, they could be quite useful in nuclear physics studies.
“Muonic atoms are really fascinating!” says co-author Odile Smits from UQ.
Smits says that muons can be created in the lab or by cosmic rays. When they are made to orbit an atomic nucleus, they orbit much closer than their lighter electron counterparts. This means they feel the structure of the nucleus in greater detail than electrons, illuminating this inner structure for physicists.
The drawback is that physicists have been unsure about how nuclear polarisation could impact studies of small energy splitting – called the hyperfine structure – in muonic atoms. Nuclear polarisation distorts the shape of the nucleus, like the moon’s gravity which creates tides on Earth.
“Our work has shown that the nuclear polarisation effect in muonic atoms is far smaller than previously considered,” Smits says.
“This opens the way for new experiments that will deepen our understanding of nuclear structure and fundamental physics,” says team leader Jacinda Ginges, also from UQ.
