The atomic bomb has been used since World War 2. The First type was called The Little Boy, and it had a gun type structure and with an uranium core. The Little boy was dropped on Hiroshima. The second type of the atomic bomb we had was called Fat Man. This bomb had a plutonium core, and it was an implosion-type device.
Radiation is energy going through the universe. The most common thing that gives out radiation is the Sun. Which gives us heat, suntans, and most importantly light. The radiation from the sun comes from ultraviolet wave lengths, and those ultraviolet rays are the things that give us the heat and lighting. So, if you were exposed to the Sun way to long, then it could become hazardous. The level of radiation when you get a sunburn or sun poisoning, is called ionizing radiation. Radiation could be even be used for medicine. The radiation they get for the medicines, come from rocks, the Earth itself, and even the air surrounding us. In a way, radiation can help us too. Doctors and dentists use radiation in X-rays for a patient. and people who have certain types of sicknesses use radiation for cures. Source 2: http://www.world-nuclear.org/info/Safety-and-Security/Radiation-and-Health/Radiation-and-Life/