Astrophysics (Index)About

potassium/thorium ratio

(K/Th ratio)
(indication of thermal history)

The potassium/thorium ratio (K/Th ratio) compares the ratio of two elements that differ in volatility, i.e., boiling points: potassium is more volatile and thorium more of a refractory material. Within the solar system, a lack of potassium (as compared to thorium) suggests at some time, the temperature was such that potassium boiled away. Their long-half-life radioactive isotopes allow them to be detected by gamma-ray spectrometers "from some distance", e.g., planetary probes.

Further reading: