An atom that defies theory

Magic exists. At least, according to theoretical research in nuclear physics, which more than seventy years ago identified the “magic numbers”: 2, 8, 20, 28, 50, 82 and 126. These represent the ideal number of neutrons or protons to ensure an increased number of neutrons or protons. Stability of isotopes of various chemical elements. It still has to be verified in the laboratory!

In the magazine nature, An international team reported for the first time the formation of oxygen-28 (²⁸O) Thanks to collisions made in a cyclotron at the facilities of the RIKEN Research Institute in Japan. It was a series of very active explosions that led to this ²⁸O. Calcium-48 was subjected to fragmentation that gave rise to various atoms, including fluorine-29. When applied to a liquid hydrogen target, the proton dissociates, leading to formation ²⁸Hey.

After decades of research, a development has occurred: the element obtained does not behave as predicted by theory! Instability ²⁸What a disgrace to scholars!

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

Its isotope 28O is doubly magical, as it contains 8 protons and 20 neutrons, 12 more than ¹⁶O. However, to the surprise of the scientific community, “ ²⁸“O releases four neutrons almost immediately after its formation in a cyclotron,” says Rituparna Kanungo, a professor of physics at Saint Mary’s University, still surprised.

This scientist associated with the Canadian TRIUMF cyclotron was not involved in the study, but she is very interested in it because she has also published work suggesting that magic number theory may not quite hold up. In 2009, I noticed that stability ²⁴The O was larger than expected, with a radioactive half-life of 61 milliseconds, although with a number of neutrons that was not at all “magical.”

His new works and research ²⁸Highlight the complexity of the most powerful force in nature: the one that holds protons and neutrons in the nucleus.

How does this advance science? Rituparna Kanungo reminds us that the universe is a natural cyclotron. Nuclear fusion in the Sun’s core constantly produces isotopes, the most stable isotopes found on surrounding planets. Understanding isotopes – from their formation to their decay – opens windows into the past and present of the universe, especially the atoms that make up the Earth.