# Isotopes used for radiological dating

### Radioactivity : Radioactive Dating

Radioactive hourglasses are used to date the relics of bygone civilizations, Carbon is a radioactive carbon isotope present in the atmosphere, plants and . Radioactive isotopes are effective tracers because their radioactivity is easy to In another interesting example of radioactive dating, hydrogen-3 dating has. Radiometric dating or radioactive dating is a technique used to date materials such as rocks or Isotopic systems that have been exploited for radiometric dating have half-lives ranging from only about 10 years (e.g., tritium) to over billion.

Plotting an isochron is used to solve the age equation graphically and calculate the age of the sample and the original composition. Modern dating methods[ edit ] Radiometric dating has been carried out since when it was invented by Ernest Rutherford as a method by which one might determine the age of the Earth.

## Radiometric Dating

In the century since then the techniques have been greatly improved and expanded. The mass spectrometer was invented in the s and began to be used in radiometric dating in the s. It operates by generating a beam of ionized atoms from the sample under test.

The ions then travel through a magnetic field, which diverts them into different sampling sensors, known as " Faraday cups ", depending on their mass and level of ionization.

On impact in the cups, the ions set up a very weak current that can be measured to determine the rate of impacts and the relative concentrations of different atoms in the beams. Uranium—lead dating method[ edit ] Main article: Uranium—lead dating A concordia diagram as used in uranium—lead datingwith data from the Pfunze BeltZimbabwe. This scheme has been refined to the point that the error margin in dates of rocks can be as low as less than two million years in two-and-a-half billion years.

Zircon has a very high closure temperature, is resistant to mechanical weathering and is very chemically inert. Zircon also forms multiple crystal layers during metamorphic events, which each may record an isotopic age of the event. This can be seen in the concordia diagram, where the samples plot along an errorchron straight line which intersects the concordia curve at the age of the sample.

**How Carbon Dating Works**

Samarium—neodymium dating method[ edit ] Main article: Samarium—neodymium dating This involves the alpha decay of Sm to Nd with a half-life of 1. Accuracy levels of within twenty million years in ages of two-and-a-half billion years are achievable. Potassium—argon dating This involves electron capture or positron decay of potassium to argon Potassium has a half-life of 1. Rubidium—strontium dating method[ edit ] Main article: Rubidium—strontium dating This is based on the beta decay of rubidium to strontiumwith a half-life of 50 billion years.

This scheme is used to date old igneous and metamorphic rocksand has also been used to date lunar samples. Closure temperatures are so high that they are not a concern. Rubidium-strontium dating is not as precise as the uranium-lead method, with errors of 30 to 50 million years for a 3-billion-year-old sample.

Uranium—thorium dating method[ edit ] Main article: Uranium—thorium dating A relatively short-range dating technique is based on the decay of uranium into thorium, a substance with a half-life of about 80, years. It is accompanied by a sister process, in which uranium decays into protactinium, which has a half-life of 32, years.

### How Is Radioactive Dating Used to Date Fossils? | Sciencing

While uranium is water-soluble, thorium and protactinium are not, and so they are selectively precipitated into ocean-floor sedimentsfrom which their ratios are measured. The scheme has a range of several hundred thousand years. A related method is ionium—thorium datingwhich measures the ratio of ionium thorium to thorium in ocean sediment. Radiocarbon dating method[ edit ] Main article: Carbon is a radioactive isotope of carbon, with a half-life of 5, years, [25] [26] which is very short compared with the above isotopes and decays into nitrogen.

Carbon, though, is continuously created through collisions of neutrons generated by cosmic rays with nitrogen in the upper atmosphere and thus remains at a near-constant level on Earth. The carbon ends up as a trace component in atmospheric carbon dioxide CO2. A carbon-based life form acquires carbon during its lifetime. Plants acquire it through photosynthesisand animals acquire it from consumption of plants and other animals.

When an organism dies, it ceases to take in new carbon, and the existing isotope decays with a characteristic half-life years. It measures time -like our ancestors - by using hourglasses provided by radioactivity.

In the radioactivity hourglass upper part, that gradually empties, are decaying nuclei. At the bottom part, slowly filling up, are the nuclei resulting from these decays.

CEA Radioactive hourglasses are used to date the relics of bygone civilizations, by measuring the amount of Carbon, whose decay rate allows for precise age calculations. Carbon is a radioactive carbon isotope present in the atmosphere, plants and living bodies.

Radioactive dating can also be applied to the dating of rocks as old as the Earth, of coral and volcanic lava. Anything between a few hundred years to several billion years old can be dated. The half-life is so short years that this method can only be used on materials less than 70, years old. Archaeological dating uses this method. Also useful for dating the Pleistocene Epoch Ice Ages. Assumes that the rate of Carbon 14 production and hence the amount of cosmic rays striking the Earth has been constant through the past 70, years.

These trails are due to the spontaneous fission of uranium. Enlarge tracks by etching in acid so that they may be visible with light microscope See readily with electron microscope Count the etched tracks or note track density in an area Useful in dating: Micas up to 50, tracks per cm squared Tektites Natural and synthetic manmade glass Reheating "anneals" or heals the tracks.

The number of tracks per unit area is a function of age and uranium concentration.