The atom that defies theory – Québec Science

Magic exists. At least according to theoretical research in nuclear physics, which more than 70 years ago identified “magic numbers”: 2, 8, 20, 28, 50, 82 and 126. These would represent the ideal number of neutrons or protons to increase Stability of isotopes of various chemical elements. It still had to be checked in the lab!

In the journal Nature, an international team reported for the first time on the formation of oxygen-28 (28O) thanks to cyclotron collisions at the facilities of the RIKEN research institute in Japan. It was a series of high-energy bombings that produced this 28O. Calcium-48 underwent fragmentation, creating various atoms, including fluorine-29. When projected onto a liquid hydrogen target, a proton dissociated, resulting in the formation of 28O.

And after decades of research, there is a twist: the obtained element does not behave as predicted by the theory! The instability of 28O destabilizes scientists.

As a reminder, there are different versions of the chemical elements in the periodic table. Let’s take oxygen for example: all of its forms contain the same number of protons (8), but the number of neutrons can vary – they are then called isotopes. Some isotopes are stable, others decay more or less quickly: in fact, everything depends on the balance between the number of protons and neutrons. The most common oxygen we breathe is 16O. What is particularly remarkable is that it involves “double magic” with its eight protons and eight neutrons – a very rare phenomenon.

Its counterpart 28O is also doubly magical with its 8 protons and 20 neutrons, 12 more than 16O. But to the surprise of the scientific community, “28O spits out four neutrons almost immediately after its formation in the cyclotron,” says still-surprised Rituparna Kanungo, a professor of physics at Saint Mary’s University.

This scientist, associated with the Canadian cyclotron TRIUMF, did not take part in the study, but is very interested in it because she has also published work suggesting that the magic number theory may not be entirely tenable. In 2009, she found that the stability of 24O was greater than predicted, with a radioactive half-life of 61 milliseconds, despite a number of neutrons, which was not “magical” at all.

His work and new research on 28O illustrate the complexity of nature’s most powerful force: the force that holds protons and neutrons in a nucleus.

How does this advance science? Rituparna Kanungo reminds us that the universe is a natural cyclotron. Nuclear fusion in the heart of the sun continuously produces isotopes, with the most stable ones being found on the surrounding planets. Understanding isotopes – from their formation to their decay – thus opens up insights into the past and present of the universe, particularly the atoms that make up the Earth.