Chart of Nuclides
Interactive chart of nuclides (Segrè chart): every isotope by proton and neutron number, with decay mode and half-life.
All nuclides are also available as a sortable, searchable table: List of nuclides
How to read the chart of nuclides
Each tile is one nuclide - an atomic nucleus with a given number of protons Z and neutrons N. Z increases upwards, N to the right. A row holds the isotopes of one element (same Z), a column - isotones (same N), and the diagonals running up and to the left - isobars with the same mass number A = Z + N.
The tile colour shows the main decay mode; black tiles are stable nuclides. Hovering shows the symbol and decay type, and a click (tap) opens the nuclide page with its half-life, all decay branches and the decay series.
Tile colours
- Stable
- α decay
- β⁻ decay
- EC / β⁺
- Proton emission
- Neutron emission
- Spon. fission
- Isomeric Transition (IT)
- Cluster emission
- Unknown / predicted
Where a nucleus moves after decay
| Decay | Change in Z and N | On the chart |
|---|---|---|
| α | Z − 2, N − 2 | 2 squares down and 2 to the left |
| β⁻ | Z + 1, N − 1 | 1 square up and 1 to the left (diagonally) |
| EC/β⁺ | Z − 1, N + 1 | 1 square down and 1 to the right (diagonally) |
| p | Z − 1 | 1 square down |
| n | N − 1 | 1 square to the left |
| SF | the nucleus splits into two lighter ones (and a few neutrons) | two lighter nuclides, roughly at half of Z and N |
| IT | no change - the isomer goes to the ground state | the same square |
The line of stability
Stable nuclides form a narrow band - the line of stability. For light nuclei it lies close to the line N = Z (e.g. C-12: 6 protons and 6 neutrons), while heavier nuclei need more and more neutrons (Pb-208: 82 protons and 126 neutrons), because neutrons add nuclear attraction without adding to the electrostatic repulsion between protons. Nuclides to the right of the band (below it) have too many neutrons and usually undergo β⁻ decay; those to the left (above it) have too many protons and decay by electron capture or β⁺. Beyond lead (Z = 82) there are no stable nuclides: the heaviest nuclei decay mainly by α, and the very heaviest also by spontaneous fission.
Magic numbers
The magic numbers 2, 8, 20, 28, 50, 82 and 126 (the last one known only for neutrons) are the numbers of protons or neutrons that completely fill the shells of the nucleus - such nuclei are exceptionally stable. The chart shows it: tin (Z = 50) has the most stable isotopes of all elements - 10. "Doubly magic" nuclei, with a magic number of both protons and neutrons, include He-4, O-16, Ca-40 and Pb-208.
Examples to find on the chart
- C-12 - stable, Z = N = 6; the reference for the atomic mass unit
- C-14 - two neutrons more than stable C-12, decays β⁻ to nitrogen-14
- F-18 - excess protons, β⁺ decay - used in PET scans
- Sn-120 - the most abundant of the 10 stable isotopes of tin (magic Z = 50)
- Pb-208 - doubly magic (Z = 82, N = 126), the heaviest stable nuclide
- U-238 - α decay, start of the uranium series
- Cf-252 - about 3% of nuclei decay by spontaneous fission