Isotopes as tracer in carbon dating
is a term for radiocarbon dating based on timestamps left by above-ground nuclear explosions, and it is especially useful for putting an absolute age on organisms that lived through those events.
In The Cosmic Story of Carbon-14 Ethan Siegel writes: The only major fluctuation [in carbon-14] we know of occurred when we began detonating nuclear weapons in the open air, back in the mid-20th century.
Because the cosmic ray bombardment is fairly constant, there’s a near-constant level of carbon-14 to carbon-12 ratio in Earth’s atmosphere.
Organisms at the base of the food chain that photosynthesize – for example, plants and algae – use the carbon in Earth’s atmosphere.
An isotopic tracer must behave as does the material being studied, but, in addition, it must have some distinguishing property by which it can be detected in the presence of the other material.The unstable carbon-14 gradually decays to carbon-12 at a steady rate. Scientists measure the ratio of carbon isotopes to be able to estimate how far back in time a biological sample was active or alive.This plot shows the level of carbon-14 in the atmosphere as measured in New Zealand (red) and Austria (green), representing the Southern and Northern Hemispheres, respectively.Radioactive tracers are widely used in science, engineering, and medicine in virtually any situation in which it is necessary to determine the distribution pattern or the rate of material transport.Isotope dilution, in which radioisotopes are introduced into stable isotopes of the same element and mixed, is a widely used technique for determining the volume of a system.