These differ from X-rays and gamma rays only in wave frequency and energy. Gamma rays are much more penetrating than alpha or beta particles. Neutrons are elementary particles which are emitted during certain types of nuclear reactions. Neutrons have no charge and are also highly penetrating. The primary quantity of interest in radiation protection is dose equivalent.
Dose equivalent is the product of the absorbed dose and the QF for that type of radiation.
It expresses the risk of harm resulting from exposure to different types of radiation on a common scale. The basic unit of dose equivalent is the rem. Natural Sources of Radiation Radiation is emitted by radioactive elements naturally present in the soil, water, and air. By virtue of their presence in the environment, radionuclides are found all the way up the food chain to humans. Building materials, like granite, contain radioactive thorium-232.