In 1972, in my first nuclear engineering class, I was handed a copy of the KAPL Chart of the Nuclides — a large poster produced by Knolls Atomic Power Laboratory that maps every known nuclide on a grid of protons (Z) against neutrons (N), color-coded by half-life. I got my engineering degree in 1975 and went to work. The chart stayed in my head.
In 1987, when HyperCard was new, I attempted a digital version. It got as far as a few stacks before the limitations of 1980s hardware made a full implementation impractical.
In 2011 I bought the wall chart — the real thing, printed large. I hung it and stared at it for several months. I had no implementation epiphany. The data alone would have taken weeks to enter by hand.
In 2025, two things changed. The IAEA began publishing its Live Chart of Nuclides as a machine-readable dataset. And AI-assisted development made it practical to build complex interactive tools in a fraction of the former time. This is the result: a browser-native recreation that loads the full IAEA dataset — roughly 4,000 nuclides — and lets you explore it with pan, zoom, and element navigation.
Each cell's background shows how long that nuclide survives before decaying. The scale runs from black (perfectly stable) through blue and green to amber, orange, and red (fractions of a second).
The original KAPL chart used a cream-to-brown palette designed for white paper. This version uses a cool-to-warm spectral scale designed for dark screens: blue for geologically old nuclides (uranium-238 has a half-life of 4.5 billion years), shifting to red for the most short-lived.
Start at the periodic table. Click any element to open the nuclide chart centered on that element's isotopes. On the chart, drag to pan and scroll to zoom. Hover any cell for details; click to open a data panel on the right. The σ XS button switches to a thermal neutron cross-section color mode, showing which isotopes are strong neutron absorbers (reactor physics view).
| Data source | IAEA Live Chart of Nuclides (CSV export, ~4,000 entries) |
| Rendering | HTML5 Canvas — no frameworks, no build step |
| Navigation | Periodic table (HTML/CSS grid) → chart with Z parameter |
| Offline use | Bundled nuclides.js ships with the page; IAEA fetch is a fallback |
| Cross sections | Thermal (2200 m/s) neutron cross sections, IAEA data |
| Author | alanhalley.com |