Natural background

Gamma spectrum of natural background radiation refers to the range of gamma-ray energies emitted by naturally occurring radioactive materials and cosmic sources present in the environment. This spectrum typically includes characteristic gamma-ray peaks from isotopes such as potassium-40 (K-40), uranium-238 (U-238) decay series, thorium-232 (Th-232) decay series, and contributions from cosmic rays. Prominent gamma peaks include 1460 keV from K-40, 2614 keV from Tl-208 (in the Th-232 decay series), and multiple peaks from Bi-214 and Pb-214 (in the U-238 decay series).

The natural background spectrum is also characterized by the cumulative contributions of gamma rays from all daughter isotopes within these decay chains. This creates a continuous "hump" or continuum at lower energies, caused by the overlapping of numerous weak gamma lines. This feature is highly variable and depends on the local environment but is typically not analyzed in detail due to its complexity and lack of distinct energy peaks.

Natural background radiation is found everywhere in the environment, as it originates from natural sources such as soil, rocks, building materials, water, air, and cosmic rays. Specific areas with high concentrations of uranium, thorium, or potassium-containing minerals have elevated levels of gamma radiation. Cosmic contributions are more significant at higher altitudes. Natural background gamma radiation is also encountered in indoor environments, often influenced by building materials.