The human body is constantly exposed to natural radiation (e.g. from space, the soil and buildings), also known as background radiation. All ionising radiation, whether electro- magnetic (gamma-γ) or corpuscular (particles in the form of alpha-α or beta-β), and neu- trons, are harmful to the human body. The unit “absorbed dose” (D) defines the effect of radiation on various substances. D is the absorbed dose in J/kg or Gray (Gy). The biological damage done by the various types of ionising radiation, α, β, γ or fast neu- trons, differs and depends on the quality factor (Q). The unit to which the damage quality factor is applied is the equivalent dose H. The equivalent dose is the product of absorbed dose (D) and quality factor (Q), so the equi- valent dose is calculated as H = D x Q [Sv], (Sv = Sievert). The Q factors for various types of radiation are indicated in table.