A trace radioisotope is a

radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable. This excess energy can be used in one of three ...

that occurs naturally in trace amounts (i.e. extremely small). Generally speaking, trace radioisotopes have

half-lives Half-life is a mathematical and scientific description of exponential or gradual decay. Half-life, half life or halflife may also refer to: Film * ''Half-Life'' (film), a 2008 independent film by Jennifer Phang * '' Half Life: A Parable for t ...

that are short in comparison with the

age of the Earth The age of Earth is estimated to be 4.54 ± 0.05 billion years. This age may represent the age of Earth's accretion (astrophysics), accretion, or Internal structure of Earth, core formation, or of the material from which Earth formed. This dating ...

, since

primordial nuclide In geochemistry, geophysics and nuclear physics, primordial nuclides, also known as primordial isotopes, are nuclides found on Earth that have existed in their current form since before Earth was formed. Primordial nuclides were present in the ...

s tend to occur in larger than trace amounts. Trace radioisotopes are therefore present only because they are continually produced on Earth by natural processes. Natural processes which produce trace radioisotopes include

cosmic ray Cosmic rays or astroparticles are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the ...

bombardment of stable nuclides, ordinary

alpha Alpha (uppercase , lowercase ) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter ''aleph'' , whose name comes from the West Semitic word for ' ...

and

beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. For example, beta decay of a neutron ...

of the long-lived heavy nuclides,

thorium-232 Thorium-232 () is the main naturally occurring isotope of thorium, with a relative abundance of 99.98%. It has a half life of 14.05 billion years, which makes it the longest-lived isotope of thorium. It decays by alpha decay to radium-228; its de ...

uranium-238 Uranium-238 ( or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, it i ...

, and

uranium-235 Uranium-235 ( or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists in nat ...

spontaneous fission Spontaneous fission (SF) is a form of radioactive decay in which a heavy atomic nucleus splits into two or more lighter nuclei. In contrast to induced fission, there is no inciting particle to trigger the decay; it is a purely probabilistic proc ...

, and

nuclear transmutation Nuclear transmutation is the conversion of one chemical element or an isotope into another chemical element. Nuclear transmutation occurs in any process where the number of protons or neutrons in the nucleus of an atom is changed. A transmutat ...

reactions induced by natural radioactivity, such as the production of

plutonium-239 Plutonium-239 ( or Pu-239) is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main iso ...

and

uranium-236 Uranium-236 ( or U-236) is an isotope of uranium that is neither fissile with thermal neutrons, nor very good fertile material, but is generally considered a nuisance and long-lived radioactive waste. It is found in spent nuclear fuel and in ...

from

neutron capture Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, wh ...

natural uranium Natural uranium (NU or Unat) is uranium with the same isotopic ratio as found in nature. It contains 0.711% uranium-235, 99.284% uranium-238, and a trace of uranium-234 by weight (0.0055%). Approximately 2.2% of its radioactivity comes from ura ...

Elements

The elements that occur on Earth only in traces are listed below. Isotopes of other elements (not exhaustive): *

Tritium Tritium () or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with a half-life of ~12.33 years. The tritium nucleus (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus of the ...

* Beryllium-7 * Beryllium-10 *

Carbon-14 Carbon-14, C-14, C or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic matter is the basis of the radiocarbon dating method pioneered by Willard Libby and coll ...

Fluorine-18 Fluorine-18 (18F, also called radiofluorine) is a fluorine radioisotope which is an important source of positrons. It has a mass of 18.0009380(6) u and its half-life is 109.771(20) minutes. It decays by positron emission 96.7% of the time and el ...

Sodium-22 There are 20 isotopes of sodium (11Na), ranging from to (except for the still-unknown 36Na and 38Na), and five isomers (two for , and one each for , , and ). is the only stable (and the only primordial) isotope. It is considered a monoisotopi ...

Sodium-24 There are 20 isotopes of sodium (11Na), ranging from to (except for the still-unknown 36Na and 38Na), and five isomers (two for , and one each for , , and ). is the only stable (and the only primordial) isotope. It is considered a monoisotopi ...

* Magnesium-28 * Silicon-31 * Silicon-32 *

Phosphorus-32 Phosphorus-32 (32P) is a radioactive isotope of phosphorus. The nucleus of phosphorus-32 contains 15 protons and 17 neutrons, one more neutron than the most common isotope of phosphorus, phosphorus-31. Phosphorus-32 only exists in small quantiti ...

* Sulfur-35 * Sulfur-38 * Chlorine-34m * Chlorine-36 * Chlorine-38 * Chlorine-39 * Argon-39 * Argon-42 * Calcium-41 * Iron-52 * Cobalt-55 * Nickel-59 * Copper-60 * Germanium-64 * Selenium-79 * Krypton-81 *

Strontium-90 Strontium-90 () is a radioactive isotope of strontium produced by nuclear fission, with a half-life of 28.79 years. It undergoes β− decay into yttrium-90, with a decay energy of 0.546 MeV. Strontium-90 has applications in medicine a ...

* Rhodium-105

References

Radioactivity {{radioactivity-stub