Radiation

What is radiation? Sunlight is radiation. Sunlight shines in the visible light range, in the ultraviolet (UV), in the infrared (IR), in the radio frequency, x-rays, etc. This is all radiation. Your reading lamp radiates light. Your red-hot stove top radiates light. Fire radiates light. A fire hydrant radiates water. A shower head, for that matter, radiates water. Radiation does not necessarily mean the emission of light. In fact, radiation was first considered as a physical phenomenon when a lump of radium was placed in a desk drawer with some photographic film. The film became exposed without sunlight! Radium decays by alpha decay, the emission of an alpha particle. In fact, there are a variety of forms of radiation, historically named alpha, beta, and gamma because they didn't know what caused the different forms. Each form causes damage in a slightly different way. In the next few sections, we will consider the forms of radiation and the result of each radiation on the radiative material. Then, we can consider how much radiation occurs and how long it takes for radioactive material to not be radioactive anymore as well as what it means to not be radioactive. Finally, the units and biological effects of radiation will be presented. Before we begin, recall that a nucleus is comprised of protons and neutrons. Our notation for the number of protons and neutrons is as follows. Every element reacts differently to chemical processes. The number of protons is what controls how it reacts. Therefore an element is defined by the number of protons. Gold always has 79 protons. Silver always has 47 protons. Oxygen always has 8 protons. Nitrogen, 7; carbon, 6; hydrogen, 1; helium, 2; radium, 88; and radon, 86. So, the number of protons is called the ``atomic number'' and is redundant with the atomic symbol: <sub>79</sub>Au, <sub>47</sub>Ag, <sub>8</sub>O, <sub>7</sub>N, <sub>6</sub>C. Atoms with different numbers of protons are different elements. However, the chemistry does not depend on the number of neutrons. Carbon with 6 neutrons is chemically equivalent to carbon with 8 neutrons. Elements (atoms with the same number of protons) with different numbers of neutrons are called isotopes. We could denote elements according to their number of protons and neutrons, <sub>6</sub>C<sub>6</sub> versus <sub>6</sub>C<sub>8</sub>, but we usually don't. Rather than the number of neutrons, we usually denote the number of nucleons: the sum of protons and neutrons. Since all nucleons (protons and neutrons) have essentially the same mass and that mass is 2000 times larger than the mass of the electrons, the nucleon number is related to the mass of the element. So, the ``mass number'' is used rather than the neutron number: ₆C ¹² (12-6=6) versus ₆C ¹⁴ (14-6=8). Since the proton number is redundant with the symbol, denoting an isotope of an element is usually shortened to C ¹² versus C ¹⁴.