Nuclear Stability
Making the heavier elements requires conditions that strike a precarious balance between stability and instability.
Let’s explain those concepts before going on with the story. Systems tend to move from instability toward greater stability. As a system becomes more stable it releases energy. A ball on the top of a hill rolls to the bottom. As the ball does so its gravitational potential energy becomes the energy of motion. When it reaches the bottom the ball comes to a stop because of friction. Friction makes heat energy. The energy of the ball’s motion disperses itself as slightly faster motion of the molecules in the ball and in the earth at the bottom of the hill. The ball and the earth are slightly warmer than they were before the ball rolled down the hill. The extra heat quickly dissipates. The ball and earth return to their normal temperature.
The ball at the top of the hill is unstable. A slight push is enough to get it rolling. At the bottom the ball is stable. After a kick it comes to rest again. The potential energy it had at the top of the hill quickly becomes unavailable for any useful purpose soon after the ball comes to rest at the bottom of the hill.
Instability Releases Energy
Free neutrons break up into protons, electrons, and neutrinos. Neutrons are stable when they combine with protons to form nuclei. A particularly stable nucleus is a pair of protons with a pair of neutrons. That is a helium nucleus. Some of the most stable of the lighter nuclei are those that may be built up from several helium nuclei. The most abundant forms of carbon, oxygen, neon, magnesium, silicon, and sulfur have the same number of protons and neutrons as three, four, five, six, seven, or eight helium nuclei respectively.
Let’s explain those concepts before going on with the story. Systems tend to move from instability toward greater stability. As a system becomes more stable it releases energy. A ball on the top of a hill rolls to the bottom. As the ball does so its gravitational potential energy becomes the energy of motion. When it reaches the bottom the ball comes to a stop because of friction. Friction makes heat energy. The energy of the ball’s motion disperses itself as slightly faster motion of the molecules in the ball and in the earth at the bottom of the hill. The ball and the earth are slightly warmer than they were before the ball rolled down the hill. The extra heat quickly dissipates. The ball and earth return to their normal temperature.
The ball at the top of the hill is unstable. A slight push is enough to get it rolling. At the bottom the ball is stable. After a kick it comes to rest again. The potential energy it had at the top of the hill quickly becomes unavailable for any useful purpose soon after the ball comes to rest at the bottom of the hill.
Instability Releases Energy
Free neutrons break up into protons, electrons, and neutrinos. Neutrons are stable when they combine with protons to form nuclei. A particularly stable nucleus is a pair of protons with a pair of neutrons. That is a helium nucleus. Some of the most stable of the lighter nuclei are those that may be built up from several helium nuclei. The most abundant forms of carbon, oxygen, neon, magnesium, silicon, and sulfur have the same number of protons and neutrons as three, four, five, six, seven, or eight helium nuclei respectively.