Have you heard of the words "radiation", "radioactivity", "radioactive substance" in the news? While we do not know the clear meaning, we think that we have some image of "danger", but is it really "dangerous"?
Radiation can not be seen by the eyes, can not be touched, doesn't have smell. It means humans can not perceive with five senses. However, we live in the presence of radiation even now and we can not reduce the amount of radiation we receive. Radiation comes from outer space, from the earth, air, food and so on. Radiation such as X-rays is als used to visualize inside of a human body or materials.
Atoms are in an unstable state with high energy. Gradually, the nucleus at the center releases high-speed particles and electromagnetic waves, and it becomes a stable state. At this time, the high energy released and the particles that fly at high speed and the electromagnetic waves of short wavelength are called "radiation." Among the radiation, there are alpha ray (α ray), beta ray (β ray), gamma ray (γ ray), X ray, neutron ray. Alpha rays, beta rays, neutron rays are particles, gamma rays and X rays are electromagnetic waves. Radiation has the ability to penetrate materials, but we can also stop it. Its characteristics depends on the type of radiation.
Source:http://www.fepc.or.jp/nuclear/houshasen/houshanou/shurui/index.html
The ability of a radioactive substance to emit radiation is called "radioactivity", an atom having radioactivity is called "radioactive element", and a substance containing it is called "radioactive substance." Even if a person receives radiation, radiation does not stay in the body and a person does not emit radiation due to receiving radiation. In the unlikely event that a radioactive substance is attached to clothes or body, you can wash it by taking a shower or washing clothes. Nuclear power plants are conducting radiation management so as to minimize the amount of radiation received as much as possible in accordance with the nature of these radiations.
Radioactive substances decrease in quantity over time and radiation level is lowered. There is physical rule how the amount of radioactive substances prereduced, and the time to reduce the amount of radioactivity by half is called "half-life." According to the type of radioactive material, the half-life is the same.
Source:http://www.fepc.or.jp/nuclear/houshasen/houshanou/index.html