Radiation is an important natural phenomenon. Historically, radiation was the key to the first hints about the nature of the atom’s internal structure. Some atomic nuclei are unstable. That means that they emit particles and/or high-energy light spontaneously. All elements of atomic number 84 and higher are radioactive. Most other elements have radioactive isotopes.
You have been told that atoms do not gain or lose protons or neutrons. This is true if only chemical reactions are considered. There are two main types of nuclear reactions in which atoms gain or lose protons and neutrons. First, there is natural radioactive decay. In radioactive decay a heavy atom emits a particle or breaks up into 2 pieces without outside interference. Second, there is nuclear transmutation. Nuclear transmutation occurs when nuclei are bombarded with protons, neutrons or other atomic nuclei. In this process people can (and have) converted one element into another.
In this activity you will learn about different types of nuclear reactions and how to write and balance equations describing them.
| Radioactive Particles/Processes | ||
| Type | Symbol(s) | Description |
| Alpha | α,4 2α, 4 2He 2+ | this is a type of atomic fission (when atoms split into two parts); it is really just the nucleus of a helium atom without any electrons; it results in the loss of two protons and two neutrons from the nucleus |
| Beta (electron) | 0 -1β, 0 -1e- | this is the emission of an ordinary electron from the nucleus; it results in the conversion of a neutron to a proton; it happens in nuclides with too many neutrons—when n0/p+ is too high |
| Beta (positron) | 0+1β, 0+1e+ | this is the emission a particle like an electron but with a positive charge: a positron; it results in the the conversion of a proton into a neutron; it happens in nuclides with too many protons— when n0/p+ is too low |
| Gamma | γ,0 0γ | this is the emission of a photon (a particle of light) with a very high energy; it has no effect on the nature of the nucleus and is simply the release of energy; other kinds of radioactive decay sometimes also include gamma rays |
| Neutron | n0,1 0n | neutrons can be emitted as part of a nuclear fission process in which a single nucleus splits into smaller nuclei |
| Proton | 1 1p, 1 1H | emitted protons are not natural radiation; they result from nuclear transmutation |
| Electron Capture | 0 -1e- | this process occurs when an electron is absorbed by the nucleus; the electron so ‘captured’ combines with a proton to produce a neutron |
In Alpha Decay the nucleus of an atom splits into two parts. One of these parts (the α particle) flies away. The nucleus that is left behind is has its atomic number reduced by two and its mass number reduced by four. This is because an α particle is a helium nucleus consisting of two protons and two neutrons. Here is an example of an alpha decay process:
The atom on the left side of the equation is the one that splits into two pieces. In alpha decay one of the two atoms on the right is always an α particle. Here is the key to getting these equations right: The other atom on the right always goes down by two in the atomic number and four in the mass number. Find the element that has the atomic number you calculate and use its symbol. Here is another example:
In Beta Decay a neutron in the nucleus of an atom breaks down (decays). When it does this, it becomes a proton. It emits an electron and an anti-neutrino. (Don’t worry about what the anti-neutrino is doing here.) The nucleus that is left shows an increase of one in the atomic number. The atomic mass number is unchanged. Here is an example of an beta decay process:
The nuclide that decays is the one on the left-hand side of the equation. Notice that the resulting nucleus has an atomic number one greater than the decaying nucleus. The -1 (β) and 7 (N) add up to the 6 (C). Here is another example: