Radioactive decay happens to somechemical elements. Mostchemical elements are stable. Stable elements are made up ofatoms that stay the same. Even in achemical reaction, the atoms themselves do not ever change.

In the 19th century,Henri Becquerel discovered that some chemical elements have atoms that change over time. In 1898,Marie andPierre Curie called this phenomenon radioactive decay.^[1] Becquerel and the Curies were awarded theNobel Prize in Physics for this discovery, in 1903.

Mostcarbon atoms have sixprotons and sixneutrons in theirnucleus. This carbon is called carbon-12s (six protons + six neutrons = 12). Itsatomic weight is 12. If a carbon atom has two more neutrons it iscarbon-14. Carbon-14 acts chemically like other carbon, because the six protons and six electrons are what govern itschemical properties.^[source?]

In fact, carbon-14 exists in all living things; all plants and animals contain carbon-14. However, carbon-14 isradioactive. It decays bybeta decay to becomenitrogen-14. Carbon-14, in the small amounts found about us in nature, is harmless. Inarchaeology, this kind of carbon is used to determine the age of wood and other formerly living things. The method is calledradiocarbon dating.^[source?]

Ernest Rutherford found that there are different ways in which these particles penetrate matter. He found two different kinds, which he calledalpha decay andbeta decay.^[2]Paul Villard discovered a third kind in 1900. Rutherford called itgamma decay, in 1903.^[3] The change from radioactive carbon-14 to stablenitrogen-14 is a beta decay. It happens when the atom emits a beta particle. Abeta particle is a high energy electron orpositron leaving the nucleus.^[source?]

Other kinds of decay were discovered later. The types of decay are different from each other because different types of decay produce different kinds of particles. The starting radioactive nucleus is called the parent nucleus and the nucleus that it changes into is called the daughter nucleus. The high-energy particles produced by radioactive materials are calledradiation. These various kinds of decay can happen sequentially in a "decay chain". One kind of nucleus decays to another kind, which decays again to another and so on until it becomes a stableisotope and the chain comes to an end.^[source?]

The speed at which this change happens, is different for each element. Radioactive decay is governed bychance: The time it takes, on average for half the atoms of a substance to change is named thehalf-life. The rate is given by anexponential function. As an example,iodine (¹³¹I) has a half-life of about 8 days. That ofplutonium ranges between 4 hours (²⁴³Pu) and 80 million years (²⁴⁴Pu).^[4]

Radioactive decay changes an atom from one that has higher energy inside its nucleus into one with lower energy. The change of energy of the nucleus is given to the particles that are created. The energy released by radioactive decay may either be carried away by agamma rayelectromagnetic radiation (a type of light), abeta particle or analpha particle. In all of those cases, the change of energy of the nucleus is carried away. And in all those cases, the total number of positive and negative charges of the atom's protons and electrons sum tozero before and after the change.^[source?]

During alpha decay, theatomic nucleus releases analpha particle. Alpha decay causes the nucleus to lose two protons and neutrons respectively. Alpha decay causes the atom to change into anotherelement as the atom loses two protons and neutrons respectively.^[source?]

For instance, ifAmericium were to go through alpha decay it would change intoNeptunium because Neptunium is defined by having two protons fewer than Americium. Alpha decay usually happens in the most heavy elements, such asuranium,thorium,plutonium andradium. Alpha particles cannot even go through a fewcentimeters of air. Alpha radiation cannot hurt humans when the alpha radiation source is outside thehuman body, because human skin does not let the alpha particles go through. Alpha radiation can be very harmful if the source is inside the body, such as when people breathedust orgas consisting of materials which decay by emitting alpha particles (radiation).^[source?]

There are two kinds ofbeta decay, beta-plus and beta-minus. In beta-minus decay, the nucleus gives out a negatively charged electron and a neutron changes into a proton:

${\displaystyle n^0\to p^{+}+e^{-}+{\overline{\nu }}_e}$.

where

${\displaystyle n^0}$ is the neutron

${\displaystyle p^{+}}$ is the proton

${\displaystyle e^{-}}$ is the electron

${\displaystyle {\overline{\nu }}_e}$ is the anti-neutrino

Beta-minus decay happens innuclear reactors.

In beta-plus decay, the nucleus releases apositron, which is like an electron but it is positively charged, and a proton changes into a neutron:

${\displaystyle p^{+}\to n^0+e^{+}+{\nu }_e}$.

where

${\displaystyle p^{+}}$ is the proton

${\displaystyle n^0}$ is the neutron

${\displaystyle e^{+}}$ is thepositron

${\displaystyle {\nu }_e}$ is theneutrino

Beta-plus decay happens inside the sun and in some types ofparticle accelerators.

Gamma decay happens when a nucleus produces a high-energy packet of energy called agamma ray. Gamma rays do not haveelectrical charge, but they do haveangular momentum.^{[clarification needed]} Gamma rays are usually emitted from nuclei just after other types of decay.

Gamma rays can be used to see through material, to killbacteria infood, to find some types ofdisease, and to treat some kinds ofcancer. Gamma rays have the highestenergy of anyelectromagnetic wave, and gamma ray bursts fromspace are the most energetic releases of energy known.

• Half-life
• Atomic physics
• Nuclear physics
• Ionizing radiation
• Radiometric dating
• Nuclear binding energy
• Mass-energy equivalence
• Transmutation

• Physics
• Science
• Nuclear physics

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