The source of radiation is the environment in which humans live. It is divided into naturally occurring radiation and artificially produced radiation.
1, naturally occurring radiation. This refers to the radiation that exists naturally in the human living environment. Including cosmic rays, radiation from the surface of the earth, the radiation in the human body. Some of this radiation comes from the sun and other planets, and our bodies themselves radiate radiation lines, natural radiation is harmless to health.
2. Artificially produced radiation. This is the radiation produced by the environment in which human beings live, such as computer radiation, cell phone radiation, home appliance radiation, as well as medical radiation, and medical radiation. Human beings are enjoying the convenience brought by electromagnetic radiation, but at the same time, they are also constantly with its negative effects. In our country, the dose of natural radiation accounts for 81.2% of the radiation dose in the middle of life, while the dose of artificial radiation grades 18.8%. Therefore, unless it is with the personal living environment and dietary habits, or through certain industrial environment or medical needs of the long exposure, and the accumulation of radiation damage, general life in the electromagnetic radiation can be without much worry.
Expanded
Based on the relationship with the field source, electromagnetic waves can be divided into two kinds of bound electromagnetic waves and free electromagnetic waves. Bound electromagnetic waves are mainly concentrated in the vicinity of the field source and exist in the form of an induction field. Its energy is not only converted between the two forms of electrical and magnetic energy, but also converted between the field source and the surrounding space, but there is no power to propagate to the distance. The energy of a free electromagnetic wave is able to travel away from the field source and propagate to a distance in the form of an electromagnetic wave whose electromagnetic field is called a radiation field. In the vicinity of the source, the energy of the bound electromagnetic wave is much greater than that of the free electromagnetic wave, while away from the source, the latter is much greater than the former.
Electromagnetic radiation is related to the frequency of the wave source, and when the frequency of the oscillating source that produces the electromagnetic waves is increased so that its wavelength can be compared to the size of the antenna (radiator), the radiated energy grows significantly. The strength of the radiation is also related to the shape and distribution of the wave source. The extent of the induced field is related to the wavelength λ. In the region where the distance to the source is less than λ/2π, the induced field is basically dominant, and is therefore also called the near region. And the radiation field is correspondingly called the far zone.
Baidu Encyclopedia - Radiation