Uses of mass spectrometry in radioactive dating
Another way of expressing this is the half-life period (given the symbol T).
The half-life is the time it takes for half of the parent atoms to decay.
The isotopes are then measured within the same machine by an attached mass spectrometer (an example of this is SIMS analysis).
This is a common dating method mainly used by archaeologists, as it can only date geologically recent organic materials, usually charcoal, but also bone and antlers.
However, potassium is very mobile during metamorphism and alteration, and so this technique is not used much for old rocks, but is useful for rocks of the Mesozoic and Cenozoic Eras, particularly unaltered igneous rocks.
Argon-Argon dating (39Ar-40Ar) This technique developed in the late 1960s but came into vogue in the early 1980s, through step-wise release of the isotopes.
Radioactive decay is a natural process and comes from the atomic nucleus becoming unstable and releasing bits and pieces.
These are released as radioactive particles (there are many types).For an element to be useful for geochronology (measuring geological time), the isotope must be reasonably abundant and produce daughter isotopes at a good rate.Either a whole rock or a single mineral grain can be dated.This technique uses the same minerals and rocks as for K-Ar dating but restricts measurements to the argon isotopic system which is not so affected by metamorphic and alteration events. The decay of 147Sm to 143Nd for dating rocks began in the mid-1970s and was widespread by the early 1980s.It is useful for dating very old igneous and metamorphic rocks and also meteorites and other cosmic fragments.Radiocarbon dating is normally suitable for organic materials less than 50 000 years old because beyond that time the amount of 14C becomes too small to be accurately measured.