Radioactive nuclei with extreme neutron-to-proton ratios—rare isotopes—often decay within fractions of a second. Typically, they are not found on Earth unless produced at an accelerator. Yet nature produces copious amounts of them in supernovae and other stellar explosions in which the rare isotopes, despite their fleeting existence and small scale, imprint their properties. Large amounts of them also exist as stable layers in the crusts of neutron stars.
Rare isotopes are therefore intimately linked to fundamental questions in astrophysics. An example is the origin of the 50-odd naturally occurring elements between the iron region and uranium in the periodic table. As figure 1 shows, with recent progress in stellar spectroscopy and the continuing discovery of very old and chemically primitive stars, a “fossil record” of chemical evolution is now emerging. Nuclear science needs to make its own progress to match specific events to the observed elemental abundance patterns produced in...
