Types of radiation
Stable/unstable isotopes: Unstable if the atomic number is greater than 83 or if the ratio of neutrons to protons places it outside the zone of stability (1:1.3 – 1:1.5).
Alpha: Ionizing radiation emitted by some substances undergoing radioactive decay. It is in fact a helium nucleus with a +2 charge. It is formed when the ratio of neutrons to protons in the nucleus is too low which causes the element to be in an unstable energy state.
Alpha radiation is unable to penetrate paper as shown in the diagram. Despite their inability to cause damage from outside the body, if ingested they are able to ionise the particles within the body as it has a positive charge.
Likewise with alpha particles being unable to penetrate through paper or human skin they cannot travel more than a few inches through air from the source.
Examples of alpha emitters are uranium, radium
U ---- > He + Th Uranium ---- > Helium + Thorium
Ra ---- > He + Rn Raidum ----- > Helium + Radon
Beta: Is also an ionizing radiation which is an electron with a charge of -1. This release occurs when there are too many neutrons in the nucleus again causing the atom to become unstable. In this case a neutron is broken up into a proton and an electron. The proton stays within the nucleus while the electron is emitted as radiation.
As shown in the diagram beta particles can penetrate through the paper but not human skin again needing ingestion or access through a cut in the skin to be harmful. They are able to travel further than Alpha particles but only up to a few meters in air.
n ----- > p + e
Co ----- > Ni + e
C ----- > N + e
Examples of beta emitters are cobalt-60, strontium-90, technetium-99, iodine-129 and -131
Gamma: Like Alpha and Beta particles Gamma radiation is an ionizing radiation, although they do not have a mass or charge as they consist of electromagnetic energy. Due to this they are able to travel at the speed of light and they can travel thousands of meters in air. As shown in the diagram above a thick slab of concrete is what is needed to stop this radiation, either that or several inches of lead (because of its density).
The wavelengths of gamma rays are measured in nanometres, typically from 0.03nm to 0.003nm.
The cause of this emission is when the nucleus of a radioactive atom has too much energy and this radiation usually comes after the emission of a beta particle.
Examples of gamma emitters are cobalt-60, cesium-137, and technetium-99m.
Half-life is the period of time required for half the atoms in a given sample to undergo radioactive decay; for any particular radioisotope the half-life is independent of the initial amount of the isotope present. As we would expect different isotopes will have different half-lives eg the half-life of technetium-99m is 61 days while the half-life for...