Chart of Nuclides

Coordinates

A nuclide is an atomic nucleus made up of a unique combination of neutrons and protons. Each pair of integer coordinates on the Chart of Nuclides represents an atomic nucleus. Latitude represents the number of protons in the nucleus (denoted Z), which also defines the element, while longitude represents the number of neutrons (denoted N). Along a latitude, there are different variants, isotopes, of an element.

The Stability Mountains and the Sea of Instability

The altitude above sea level represents the stability of the various nuclides. Most nuclides located along the the Stability Mountains are stable. This means that these nuclides do not decay. Nuclides located near sea level and on the Sea of Instability are unstable and decay (see next point).

Alpha, beta and gamma particles and the Radioactive Strait

The nuclides that are located close to and below sea level are unstable. This means that they are radioactive. When they decay, they emit different types of ionizing radiation such as alpha, beta and gamma particles. The lower the altitude, the shorter the lifetimes of the nuclei, in other words, the more unstable they are. Atomic nuclei in the Radioactive Strait are particularly short-lived and can have lifetimes of only microseconds. Often the radiation emitted from more unstable nuclei has higher energy. By measuring the energy of the alpha, beta and gamma particles, an insight is gained into how the atomic nucleus works and its stability. In the story, the colors of the particles symbolize their energies, from the spectrum of the rainbow with the lowest energy as red and the highest energy as purple.

Actinide Island and 244Pu

The Actinide Island hosts the heaviest naturally occurring nuclides, mainly isotopes of the elements uranium and thorium. Because they have lifetimes of billions of years, they are still found in relatively large amounts on Earth. Nuclides on the Actinide Island can decay with something called spontaneous fission. Then the nucleus splits into two lighter nuclei and a lot of energy is released. The southern fission winds in the story symbolize this creation of lighter nuclei. On the contrary, the northern fusion winds represent the fusion process, that is, when two nuclei fuse together and create a heavier nucleus. In the experiment, it is the fusion between nuclei of 244Pu and 48Ca that creates the superheavy element flerovium. 244Pu is the isotope of element 94, plutonium, with 150 neutrons.


Marked latitudes and longitudes

Atomic nuclei with a so-called magic number of protons and/or neutrons show extra stability, i.e., they are more resistant to radioactive decay and are more stable. It was Maria Göppert Mayer who first managed to explain the background to these magic numbers with the very successful shell structure model for the atomic nucleus.

Tin is an example of an element that has a magic number of protons (50) in the nucleus. Therefore, there are a large number of stable isotopes along the Tin Latitude and they are represented with high mountain peaks on the Chart of Nuclides. The largest magic numbers determined so far are 82 and 126 for protons and neutrons respectively. Atomic nuclei with this many protons and/or neutrons are found on Lead Peak, which is therefore extra high.

The next magic numbers have not yet been determined, but it has generally been predicted that atomic nuclei of the element flerovium (i.e., along the Flerovium Latitude) with 114 protons and especially the isotope with 184 neutrons may be the next nucleus with both magic numbers of protons and neutrons. Just near these magic numbers, it is possible that very long-lived, even stable, so-called superheavy nuclei exist. The search for this Island of Stability has fascinated nuclear physicists ever since it was first predicted by theorists in the late 1960s by, among others, the Lund physicist Sven-Gösta Nilsson.

Visualization

The visualization of the Chart of Nuclides is based on tabulated half-lives (Nuclear Wallet Cards Search). Fine adjustments have been made with an overlay of Gaussian peaks and shell structure correction (P. Möller et al., At. Data. Nucl. Data Tables 109-110, 1 (2016).) Inspiration has been taken from previous similar illustrations.