Radioactive minerals
Radioactive minerals are naturally occurring minerals that contain unstable atomic elements, primarily uranium and thorium. These minerals can be classified into primary and secondary types based on their formation processes. Primary radioactive minerals form directly from magma in the Earth's mantle, while secondary minerals arise when primary radioactive materials dissolve and re-solidify in different geological environments. Understanding the decay of these radionuclides—unstable atoms that emit radiation—is crucial for various applications, including radiometric dating and nuclear fuel production.
Radioactive decay occurs through different processes: alpha, beta, and gamma decay, each releasing specific forms of radiation. Gamma radiation is particularly concerning due to its penetrating ability and potential harm to biological tissues. The transformation of radioactive minerals over time can lead to changes in their structural characteristics, often resulting in a more amorphous form known as metamict minerals. These changes underscore the complexity of identifying and handling radioactive materials, which may pose health risks.
Radioactive minerals have significant industrial applications, especially in the nuclear energy sector, where uranium is used for fuel. Emerging technologies are exploring the use of thorium as an alternative nuclear fuel due to its abundance and potential benefits, such as reduced waste and increased efficiency. As research continues, the study of radioactive minerals remains vital for advancing both scientific knowledge and practical applications in energy production.
Radioactive minerals
Radioactive minerals contain unstable atoms, such as uranium and thorium, within their crystal structure. Primary radioactive minerals form within magma pockets in the earth’s mantle while secondary radioactive minerals form when radioactive substances derived from magmitic rocks are dissolved into solution and later combine with other materials to solidify into other types of rock. Radioactive minerals are used in radiometric dating; the manufacture of metals, industrial gases, and filaments; and the development of fission reactors to derive nuclear fuel. Researchers are working on ways to derive fuel from fission involving thorium.
Radionuclides and
Atomic elements found in nature may be classified as either stable or unstable based on the energy contained within the element’s atomic nucleus. If the particles that make up the nucleus (protons and neutrons) of the atom are balanced in regard to energy, the atom is stable. If the nucleus contains excess energy it is said to be unstable or radioactive.
Unstable atoms, called radionuclides, have either excess protons or neutrons; in this case the atom will eventually emit the excess energy either by ejecting a proton or neutron into the environment; by emitting beta particles or positrons to convert protons to neutrons, or vice versa; or by emitting excess energy in the form of light radiation or photons. This stabilization process, called radioactive decay, converts the radionuclide into a more stable atom called a daughter nuclide.
Three basic types of radioactive decay exist: alpha, beta, and gamma. Each type releases a different type of radiation. Alpha decay occurs when a radionuclide emits two protons and two neutrons into the environment, referred to as alpha rays. Beta decay involves the emission of an electron or positron into the environment, which converts a proton to a neutron, or vice versa. Both alpha and beta decay contribute to the stabilization of the radionuclide and its conversion to a daughter nuclide. Gamma decay occurs in conjunction with both alpha and beta decay and involves the release of photons from the extra energy produced by alpha or beta decay.
Gamma radiation is the most damaging form of radiation to biological structures because it moves easily through the atmosphere and can be blocked only by heavy shielding. Beta and alpha radiation, conversely, travel only a short distance through the atmosphere before they are absorbed by atmospheric atoms and molecules. Therefore, most dangerous radiation is in the form of gamma radiation, though direct exposure to alpha and beta radiation, at extremely close range, can also damage biological tissues.
As unstable atoms decay, they transition into a different type of atom. The resulting material, therefore, is distinct in many characteristics from the parent material. Physicists have found that different radioactive materials decay at certain rates and that these rates can be used to determine the age of the material. Radioactive isotopes of certain atoms, like carbon, will decay into nonradioactive isotopes of carbon in a predictable time, so measuring the proportion of stable to radioactive isotopes within a sample of carbon-rich rock can be used to estimate the time that has elapsed since the rock formed.
Radioactive Mineral Formation
Radioactive minerals generally contain either thorium or uranium within their crystal structure. More than two hundred minerals have been discovered containing one of these elements. Occasionally, radioactive isotopes of phosphorus may occur in certain minerals.
Radioactive minerals can be divided broadly into primary and secondary minerals, based on their geologic origin. Primary materials are those that form within magma pockets in the earth’s mantle. Radioactive minerals are a natural product of magma and form into solid rock when magma erupts through the crust as lava or cools beneath the surface to form igneous rock deposits.
Another source of radioactive minerals are hydrothermal vents, which are areas in which magma beneath the surface heats pockets of water in the deep ocean. As this superheated water erupts through the oceanic crust, it carries a variety of minerals derived from the deeper crust and the mantle, including radioactive minerals, which later solidify into rock.
Secondary radioactive minerals are those that form when primary radioactive minerals dissolve into a solution within the soil or some aqueous environment and then re-form into solid rock of a different type. Secondary radioactive minerals are generally sedimentary rock, formed when solutions containing radioactive minerals mobilize and then become solidified and compacted through evaporation and concentration within the crust.
Radioactive uranium is well known because of its use in nuclear fission technology. The most common primary minerals containing uranium include uraninite, the silicate mineral coffinite, and the complex oxide mineral brannerite. There also exist a wide variety of secondary uranium minerals, including carbonates and silicate-based minerals. Thorium is the second most common radioactive element found in naturally occurring minerals. The most common primary minerals of thorium include thorianite, thorouraninite, and the silicate mineral uranothorite. Thorium also is included in a variety of secondary radioactive minerals and can be found in trace amounts in several minerals, including monazite, which is a phosphate mineral.
Identification and Classification of Radioactive Minerals
As radioactive minerals decay, the chemical structure of the mineral is altered, leading to subsequent changes in the structure of the crystal lattice. This process is called metamictization and leads to the formation of what geologists call metamict minerals.
Metamictization generally takes thousands of years because radioactive decay occurs at a gradual pace. In most cases, metamictization results in an amorphous mineral shape, which is a state in which the shape and structure of the crystal lattice is unclear, resulting in smoothed edges and an overall globular appearance.
Radioactive minerals containing both thorium and uranium are difficult to distinguish based on morphological characteristics and also are similar in appearance to many other types of nonradioactive minerals. This presents a difficulty because the handling and collecting of radioactive minerals can be dangerous; handling and collecting is therefore prohibited or restricted in many locations. The exact identification of radioactive materials often requires the use of X-ray diffraction, which utilizes the pattern created by X-rays focused through thin sections of a crystal to illustrate the atomic and chemical structure of the substance in question.
Many radioactive minerals appear in two general varieties: bright green or yellow minerals and amorphous and dark or cloudy colored minerals. Primary radioactive minerals are more likely to be yellow or light green because they have not yet transitioned to their eventual form through metamictization. As mentioned, radioactive minerals that have undergone significant metamictization will appear amorphous and are generally dull and cloudy in color and luster. Primary radioactive minerals are therefore easier to identify than are metamict minerals, and diffraction analysis may be required to achieve a full identification. Both primary radioactive minerals and metamict minerals may emit harmful radiation. Geologic organizations recommend caution when collecting minerals that are potentially radioactive in origin.
Uses of Radioactive Minerals
The most familiar use of radioactive minerals is in nuclear fission technology, which utilizes uranium as a source of fuel. Uranium-rich minerals such as uraninite and tobernite constitute one of the earliest material stages of the fission process, as these minerals yield sufficient uranium to produce fuel. Uranium ore is then crushed into a fine power called yellowcake, which can be further processed to derive the raw fuel for fission.
Thorium extracted from thorium-rich radioactive minerals is mixed with magnesium alloy to create stronger metallic compounds for industrial uses. This process has yielded strong metals used in aircraft construction and other applications. Because of their high melting point, thorium metals also are used as filaments in the construction of lamps and lighting technology.
Plans exist to use thorium, which is less radioactive than uranium, as a fuel for nuclear reactors. The most recent plan calls for the development of a liquid-fluoride thorium reactor (LFTR), which contains uranium and thorium in separate compartments filled with liquid fluoride salts. The uranium donates neutrons to the thorium, transforming the thorium into an isotope of uranium and producing heat energy from fission in the process. While thorium fission is still in its infancy, significant funding has been dedicated to research because of the substantial advantages of thorium versus uranium fuel.
Early research indicates that LFTRs may increase the efficiency of nuclear reactions by more than 20 percent and will require far less investment in terms of initial materials than conventional uranium reactors. In addition, thorium reactors are being designed in such a way that most of the by-products of the process can be utilized in another stage of the reactor, thereby greatly reducing the amount of nuclear waste.
Another major benefit to thorium fission is that thorium is far more abundant than uranium in the earth’s crust. Thorium is a basic component of the crust in many locations and is more abundant than many other common minerals, such as tin, silver, and mercury.
Principal Terms
alpha rays: combination of two protons and two neutrons released from a radionuclide during the radioactive decay process
beta rays: electrons or positrons released from a nucleus during the radioactive decay process
gamma rays: electromagnetic rays released from a variety of sources including the decay of unstable radionuclides, which is a form of ionizing radiation and is therefore potentially harmful to biological tissues
metamict rock: mineral that has lost its defined crystal structure during the process of radioactive decay, generally forming into an amorphous mineral
radioactive decay: process by which an unstable nucleus releases excess energy to reach a more stable state, transforming a radionuclide into a daughter nuclide
radionuclide: atom with an unstable nucleus due to a lack of balance among protons and neutrons within the atomic nucleus
thorium: naturally occurring atomic element characterized by its mildly radioactive characteristics and a decay pattern that involves the release of alpha rays into the environment
uranium: naturally occurring atomic element characterized by its highly radioactive nature and the emission of alpha, beta, and gamma rays during the decay process
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