Nuclear radiation
Types of radioactive decay
An unstable nucleus can decay by emitting an Subatomic particle comprising two protons and two neutrons (the same as a helium nucleus). (α), a A type of ionising radiation consisting of a single electron. (β), a A type of ionising radiation that is also part of the EM spectrum. It has no mass. (γ) or in some cases a single Uncharged subatomic particle, with a mass of 1 relative to a proton. The relative charge of a neutron is 0. (n).
Alpha particle
If the nucleus has too few neutrons, it will emit a 'package' of two protons and two neutrons called an alpha particle.
An alpha particle is also a Helium-4 nucleus, so it is written as 42He and is also sometimes written as 42α.
Alpha decay causes the The number of protons and neutrons found in the nucleus of an atom. of the nucleus to decrease by four and the The number of protons in the nucleus of an atom. Also called the proton number. of the nucleus to decrease by two.
Beta particle
If the nucleus has too many neutrons, a neutron will turn into a proton and emit a fast-moving Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons.. This electron is called a beta particle – this process is known as Radiation caused by beta particles (high-energy electrons). A beta particle is an electron ejected from a nucleus when a neutron becomes a proton..
A beta particle has a relative mass of zero, so its mass number is zero, and as the beta particle is an electron, it can be written as 0-1e. However sometimes it is also written as 0-1β.
Electrons are not normally expected to be found in the nucleus but neutrons can split into a positive proton (same mass but positive charge) and an electron (which has a negative charge to balance the positive charge) which is then ejected at high speed and carries away a lot of energy.
Beta decay causes the atomic number of the nucleus to decrease by one and the mass number remains the same.
Gamma ray
After emitting an alpha or beta particle, the nucleus will often still be too 'hot' and will lose energy in a similar way to how a hot gas cools down. A hot gas cools by emitting Electromagnetic radiation emitted from a hot object. which is an A transverse wave caused by oscillations in an electromagnetic field..
High energy particles will emit energy as they drop to lower Specific amounts of energy that electrons have when they orbit a nucleus is a particular shell. Electrons that gain energy may move to a higher energy level (a shell further from the nucleus). Electrons that lose energy may move to a lower energy level (a shell closer to the nucleus).. Since energy levels in the nucleus are much higher than those in the gas, the nucleus will cool down by emitting a more energetic electromagnetic wave called a A type of ionising radiation that is also part of the EM spectrum. It has no mass..
Gamma ray emission causes no change in the number of particles in the nucleus meaning both the atomic number and mass number remain the same.
Neutron emission
Occasionally it is possible for a neutron to be emitted by The process in which unstable atomic nuclei break apart or change, releasing radiation as they do so.. This can occur naturally ie absorption of cosmic rays high up in the atmosphere can result in neutron emission, or it can occur artificially, ie the work done by Sir James Chadwick firing alpha particles at Beryllium. Sir James Chadwick graduated from the University of Manchester in 1911 and went to work at the University of Cambridge where, in 1932, he discovered the neutron.
Neutron emission causes the mass number of the nucleus to decrease by one and the atomic number remains the same.
Properties of nuclear radiations
The different types of radiation are often compared in terms of their The power of the radiation that demonstrates how far into a material the radiation will go., their To ionise is to convert an uncharged atom or molecule into a charged particle by adding or removing electrons. and how far they can travel in the air.
| Symbol | Penetrating power | Ionising power | Range in air | |
| Alpha | α | Skin/paper | High | < 5 (cm) |
| Beta | β | 3 mm aluminium foil | Low | ≈ 1 (m) |
| Gamma | γ | Lead/concrete | Very low | > 1 (km) |
| Alpha | |
|---|---|
| Symbol | α |
| Penetrating power | Skin/paper |
| Ionising power | High |
| Range in air | < 5 (cm) |
| Beta | |
|---|---|
| Symbol | β |
| Penetrating power | 3 mm aluminium foil |
| Ionising power | Low |
| Range in air | ≈ 1 (m) |
| Gamma | |
|---|---|
| Symbol | γ |
| Penetrating power | Lead/concrete |
| Ionising power | Very low |
| Range in air | > 1 (km) |
All types of radioactive decay can be detected by a Geiger-Muller tube, or G-M tube. The radiations ionise the gas inside and the resulting charged particles move across the chamber and get counted as charges per second rather like an ammeter.
