Background radiation refers to the amount of radiation to which a person is exposed from natural sources. Natural sources of background radiation include radioactive substances in the soil, cosmic radiation originating in outer space, and naturally occurring radionuclides deposited in the human body. On average, a person in the United States gets a dose to the thyroid of approximately 100 millirad per yer from background radiation.
Radiation that comes from natural sources and is always present in the environment. This includes solar and cosmic radiation as well as radioactive elements in the ground, building materials, and the human body. Average annual dose of background radiation for an American is about 360 millirems.
the radiation that has always been present in the environment and is produced by natural sources such as cosmic rays and radioactive elements in the ground, building materials and the human body.
Keywords:  breakthrough, time
Breakthrough time
Keywords:  resorts, barrel, last, over
Last Resorts Over A Barrel