![]() Thus it is the time it takes for exactly half of an arbitrary quantity of that isotope to remain.Īn isotope of a chemical element which is not subject to radioactive decay is described as stable. The half-life of a radioactive isotope is the time it takes for exactly half of an arbitrary quantity of that isotope to undergo radioactive decay. ![]() However, the new atom may have its own particular (different) mode of decay itself.Īn isotope of a chemical element which is subject to radioactive decay is known as a radioactive isotope.Ī chemical element whose isotopes are all subject to radioactive decay is known as a radioactive element. Having decayed, that atom is now transformed into an atom of a different type, and so is not subject to any further occurrences of that particular decay process. The probability of an individual atom decaying is an intrinsic property of the given chemical element. Though the intrinsic radioactivity is the same, the radiation dose received by someone handling a kilogram of high grade uranium ore will be much greater than for the same exposure to a kilogram of separated uranium, since the ore contains a number of short-lived decay products (see section on Radioactive Decay).Radioactive decay is a first-order reaction in which the atoms of a substance may spontaneously break apart, thereby turning into atoms of a different substance. The air in many 100 sq metre European homes (radon)ġ household smoke detector (with americium)ġ kg 50-year old vitrified high-level nuclear waste The air in a 100 sq metre Australian home (radon) This occurs when atoms of one element break down to form another atom. Radioactivity of some natural and other materials Comparison Over time, rocks with unstable elements break down in a process called radioactive decay. * A former unit of (radio)activity is the Curie - 1 Bq is 27 x 10-12 curies. A becquerel is one atomic decay per second *. Gamma rays are often emitted with alpha or beta radiation also, as the nucleus decays to a less excited state.Īpart from the normal measures of mass and volume, the amount of radioactive material is given in becquerel (Bq), a measure which enables us to compare the typical radioactivity of some natural and other materials. The excited form is signified with an "m" (meta) beside its atomic number, eg technetium-99m (Tc-99m) decays to Tc-99. All the time, the atom is progressing in one or more steps towards a stable state where it is no longer radioactive.Īnother source of nuclear radioactivity is when one form of a radioisotope changes into another form, or isomer, releasing a gamma ray in the process. One can describe the emissions as gamma, beta and alpha radiation. If it decays with emission of an alpha or beta particle, it becomes a new element. When an atom of a radioisotope decays, it gives off some of its excess energy as radiation in the form of gamma rays or fast-moving sub-atomic particles. Some elements, eg uranium, have no stable isotopes. Unstable isotopes (which are thus radioactive) are called radioisotopes. This is called 'radioactive decay'.Įach element exists in the form of atoms with several different sized nuclei, called isotopes. An unstable atom has excess internal energy, with the result that the nucleus can undergo a spontaneous change towards a more stable form. These atoms are said to be 'unstable' or 'radioactive'. Most atoms are stable a carbon-12 atom for example remains a carbon-12 atom forever, and an oxygen-16 atom remains an oxygen-16 atom forever, but certain atoms eventually disintegrate into a totally new atom. Radiation comes from atoms, the basic building blocks of matter.
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