How do we determine the age of a rock?

Of the naturally-occuring uranium isotopes, only uranium can sustain a chain reaction— a reaction in which each fission produces enough neutrons to trigger another, so that the fission process is maintained without any external source of neutrons. Traditionally, uranium has been extracted from open-pits and underground mines. In the past decade, alternative techniques such in-situ leach mining, in which solutions are injected into underground deposits to dissolve uranium, have become more widely used.

Most mines in the U.

The milling refining process extracts uranium oxide U 3 O 8 from ore to form yellowcake, a yellow or brown powder that contains about 90 percent uranium oxide. In-situ leach mining leaves the unusable portion in the ground, it does not generate this form of waste. The total volume of mill tailings generated in the U. Moreover, the half-lives of the principal radioactive components of mill tailings, thorium and radium are long, being about 75, years and 1, years respectively. The most serious health hazard associated with uranium mining is lung cancer due to inhaling uranium decay products.

Uranium mill tailings contain radioactive materials, notably radium, and heavy metals e. Mining and milling operations in the U.

Principles of Radiometric Dating

For example, nearly one third of all mill tailings from abandoned mill operations are on lands of the Navajo nation alone. Others continue to suffer the effects of land and water contamination due to seepage and spills from tailings piles. Uranium is generally used in reactors in the form of uranium dioxide UO 2 or uranium metal; nuclear weapons use the metallic form. Production of uranium dioxide or metal requires chemical processing of yellowcake.

Further, most civilian and many military reactors require uranium that has a higher proportion of uranium than present in natural uranium. The process used to increase the amount of uranium relative to uranium is known as uranium enrichment.

Radioactivity : Uranium and

Some research reactors and all U. To enrich uranium, it must first be put in the chemical form uranium hexafluoride UF 6. After enrichment, UF6 is chemically converted to uranium dioxide or metal. A major hazard in both the uranium conversion and uranium enrichment processes comes from the handling of uranium hexafluoride, which is chemically toxic as well as radioactive. Moreover, it reacts readily with moisture, releasing highly toxic hydrofluoric acid. Conversion and enrichment facilities have had a number of accidents involving uranium hexafluoride.


The bulk of waste from the enrichment process is depleted uranium—so-called because most of the uranium has been extracted from it. Depleted uranium has been used by the U. It was incorporated into these conventional weapons without informing armed forces personnel that depleted uranium is a radioactive material and without procedures for measuring doses to operating personnel.

The enrichment process can also be reversed. Uranium metal at various enrichments must be chemically processed so that it can be blended into a homogeneous material at one enrichment level. As a result, the health and environmental risks of blending are similar to those for uranium conversion and enrichment.

User Comments

In the federal government set standards for controlling pollution from active and abandoned mill tailings piles resulting from yellowcake production. The principal goals of federal regulations are to limit the seepage of radionuclides and heavy metals into groundwater and reduce emissions of radon to the air.

Chemistry Learner

Mandatory standards for decommissioning nuclear facilities including conversion and enrichment facilities are only now being developed by the U. Environmental Protection Agency and the U. Because of the huge differences in the half lives of Carbon 14 and Uranium they cannot be used together. Carbon 14 can only be used to date fossils of a very recent age. Uranium can only be used to date volcanic rocks of a very old age. How are C and U dating used together in order to determine fossil ages?

Conversion and Enrichment

Carbon 14 and Uranium are not used together to determine fossil ages. Related questions Why does carbon 14 undergo radioactive decay? How can half-life be described in terms of radioactive decay? What are some examples of radioisotopes?

U-238 Istopic Decay Series

What is radioactive carbon dating? How can carbon 14 be used in biology? How can carbon 14 be used to date organic material? How carbon 14 dating is done? How does carbon 14 decay?