The thicker the substance, the more the radiation is absorbed.Īlpha, beta and gamma radiations penetrate materials in different ways. This is because the particles or rays become more spread out. For example, alpha radiation travels only a few centimetres in air, beta radiation travels tens of centimetres in air, and gamma radiation travels very large distances.Īll types of radiation become less intense as they travel further away from the radioactive material. Radiation can be absorbed by substances in its path.
Two protons and two neutrons bound together (identical to a helium nucleus)Ī neutral subatomic particle from a nucleus The table shows some features of the four main types of radiation: Type of radiation The particles or rays they give off are types of radiation. Substances containing unstable atoms are described as radioactive. electromagnetic radiation as gamma rays.When this happens, they emit particles or rays, including: However, some atomic nuclei are unstable and may change or break down. Since the beta particles are scattered easily by the nucleus, their paths are not straight usually.If an atomic nucleus does not change or break down, we say that it is stable.
The ability of an element to stop a beta particle depends on z / A z/A z / A. The range of a given beta particle depends not only on its initial energy but also on the number of electrons with which it collides in passing through the absorbing material. The later number depends on the density of the electron in the material. The superficial density is the actual thickness multiplied by the density. It is used as a measure of thickness. If the amount of absorbing material is expressed as the product of the density and thickness, then the range is independent of the nature of the absorber.
The range of beta particles is the distance traveled by the most energetic beta particles emitted from a radioactive substance, it corresponds to the energy at the endpoint of the continuous spectrum. Ranges of beta particles are often expressed as ‘density thickness' having units of a gram per centimeter square. The absorption curve deviates from its exponential form at the end and the point at which the curve meets the background is known as the ranges R of beta radiation. The figure plots the count (in cpm) vs absorber density thickness of beta particles. Since the mass of beta particles are identical to that of the scattering electrons, large deviations in the path of the beta particles are possible. Even a thin absorber can attenuate beta particles and get them scattered out of the direct beam. The activity becomes fractionally constant at a particular value of thickness of the absorber – this is known as the background. Activity does not decrease to zero with the increase of thickness of absorber. Μ: absorption Coefficient independent of x.Ī: activity observed after it has traversed through thickness x of the material with initial activity A0 N → p + e − ( N e g a t i v e b e t a d e c a y ) n \to p + \exp ( - \mu x) A ( x ) = A 0 exp ( − μ x ) Beta particles that are emitted by radioactive substances are generally very high energy electrons/positrons. There are three nuclear processes that are closely related and are grouped under beta decay.
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