A branch of the environmental and occupational safety health sciences and professions concerned with the protection of people and the environment from possibly harmful effects of radiation, while providing for the utilization of radiation for the benefit of society. Health physicists are interdisciplinary radiation protection and safety specialists whose expertise draws from environmental science, mathematics, medicine, radiological health, radiation biology, chemistry, and physics. The subject requires understanding of the generation, measurement, and characteristics of radiation; environmental transport of radionuclides; dosimetry; effects of radiation in biological systems; and the regulations and recommendations governing the use of radiation. The field has expanded to include nonionizing as well as ionizing sources of radiation.