Radioactive decay

The trefoil symbol is used to indicate radioactive material.

Radioactive decay is the process where the nucleus of an atom changes into another type of nucleus and produces a particle at the same time. Nuclei which change like this are called radioactive or unstable. This change happens to the nucleus of an atom. Most atoms on earth are not radioactive, but atoms with more or less neutrons than a stable atom, that is, different isotopes of the same element, can be radioactive. For example, most carbon atoms in the world have six protons and six neutrons in their nucleus. This carbon is called carbon-12, because 12 is the number of protons and neutrons. Carbon's atomic weight is 12. If two more neutrons are added to carbon-12, it becomes carbon-14. Carbon-14 is still chemically carbon, because carbon is defined by having six protons, which it still does even after the addition of more neutrons. In fact, carbon-14 exists in all living things that contain carbon, such as animals and plants. However, it is radioactive.

Radioactive decay always changes the type of atom from an isotope that has higher energy inside its nucleus to an isotope with lower energy in its nucleus. The difference in energy between the nucleus before and after the decay is given to the particles created in the decay to increase their speed, or kinetic energy. Energy is never created or destroyed in radioactive decay.

Alpha decay, beta decay and gamma decay are the most common types of radioactive decay. They are different from each other because different types of decay produce different 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 called radiation.

Alpha decay

During alpha decay, the atomic nucleus releases an alpha particle. The nucleus will lose two protons and two neutrons when this happens. After the decay, the atom will change to another element, because the atom loses two protons. For example, if Americium were to go through alpha decay it would change into Neptunium because Neptunium is defined by having two protons fewer than Americium. Alpha decay usually happens in heavy elements, those containing more neutrons and protons, such as uranium, thorium, plutonium, and radium.

Alpha particles cannot even go through a few centimeters of air. Alpha irradiation cannot hurt humans when the alpha source is outside the human 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 breathe dust or gas containing materials which decay by emitting alpha particles.

Beta decay

There are two kinds of beta 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:

$n^0 \rightarrow p^+ + e^- + \bar{\nu}_e$.

where

n⁰ is the neutron

$\ p^+$ is the proton

e ⁻ is the electron

$\bar{\nu}_e$ is the anti-neutrino

Beta-minus decay happens in nuclear reactors.

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

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

where

$\ p^+$ is the proton

n⁰ is the neutron

e ⁺ is the positron

ν_e is the neutrino

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

Gamma decay

Gamma decay happens when a nucleus produces a high-energy packet of energy called a gamma ray. Gamma rays do not have electrical charge, but they do have angular momentum. Gamma rays are usually emitted from nuclei immediately after other types of decay. Gamma rays can be used to analyze radioactive materials, to kill bacteria in food, to find some types of disease, and to treat some kinds of cancer. Gamma rays have the highest energy of any electromagnetic wave, and gamma ray bursts in space are the most energetic releases of energy known to people, even more than supernovas.