Alpha radiation which impacts the human organism externally is relatively harmless since the weak alpha particles will permeate only the upper, dead layers of the skin. Embedded alpha rays that have been inhaled or ingested with food, however, can be very harmful since living cells are being exposed (radiation cancer), not just the upper layers of skin. When alpha radiation is ingested –for instance through radioactive foods– these substances can accumulate within the body, and they can harm the genetic material and cause cancers. The alpha rays’ permeability in air extends to only a few inches.
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay. They are designated by the Greek letter beta (β). There are two forms of beta decay, β− and β+, which respectively give rise to the electron and the positron.
Their penetration power is in air several feet, through plastic, aluminum, or human tissue only a few millimeters.
Gamma radiation, on the other hand, permeates deeply into the tissue which absorbs its energy. These lead, for instance, to ionization processes which can generate secondary radiations such as electron- or X-ray radiation. These, in turn, break down chemical bonds and thereby harm genetic materials. The cellular function, however, is generally maintained even at high radiation doses. Mutations caused by cell division, nevertheless, may cause problems. Their permeability in air extends to a few miles, and it can only be diminished by dense steel- or lead barriers.
Radioactive radiation is variably harmful to humans depending on the degree, the duration, and the type of radiation. The relative biological efficiency of alpha radiation is established at 20. In comparison, the relative biological efficiencies of beta- and gamma radiation is established at 1. This means that, at the same energy input levels, alpha radiation is 20-times more harmful. Thus, alpha radiation is particularly dangerous if it permeates into the body through radioactive foods or something similar.