Decay Series One very useful way to display all the known isotopes is to create a graph with the number of protons ( Z ) along the horizontal axis and the number of neutrons, which we will give the symbol N , along the vertical axis. The stable elements form a thin, stair-stepping curve surrounded by a band of unstable elements. On this isotope graph , it can be seen that β – decay transmutes the isotope down and to the right ( ) while β + decay moves it up and to the left ( ). The vast majority of the isotope graph thus looks like the section shown at right. Notice that the radioactive isotopes generally head along a diagonal line directly toward a stable isotope (shown in black). The approximate half-life of each isotope is color-coded by the background of each cell: red is less than one second; orange is less than one day; yellow is less than one year ( 1a ); green is less than 1000a; blue is less than 10 6 a; and violet is over a million years. Technetium (element 43) may not have any stable isotopes, but
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