The Discovery Of Radiation
In the mid 1880s, James Maxwell published a mathematical description of the wave motion of heat and light, the only forms of radiation known at the time. As scientists discovered other forms of radiation (such as x rays, radio waves, microwaves, and gamma rays) they found that their physical behavior could also be described by Maxwell's equations, and that they were all part of the same, continuous, electromagnetic spectrum.
In 1895, the French physicist Henri Becquerel began experimenting with the rare metal, uranium. He eventually discovered that uranium emitted a previously unknown form of radiation. Soon after, Pierre and Marie Curie discovered radium and polonium, which are also radioactive. These discoveries led to better understanding of the structure of the atom, and it became clear that there was another kind of radiation: ionizing radiation produced by radioactive substances. This type of radiation consists of extremely high-energy particles, which are released from the nuclei of radioactive atoms as they spontaneously undergo fission (i.e., break into smaller nuclei, forming different atomic elements). (Gamma rays, a form of electromagnetic radiation, are also released by some radioactive elements.) Because there are many kinds of radiation, it is subject to different classifications. Radiation can be described as electromagnetic or particulate (i.e., radioactive). These are further classified as being either ionizing or non-ionizing, depending on their energy level.
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