Different Kinds of Fission
When a few protons and neutrons come together they release some of the energy of the strong nuclear force. On the other hand, when a nucleus becomes too big it also becomes unstable. Uranium, the heaviest naturally occurring element, may emit a helium nucleus. That reduces the number of protons in the uranium nucleus to 90, which is an unstable form of thorium. The thorium also breaks up into lighter elements.
Big nuclei have a number of ways of breaking up. We have discussed the emission or breaking away of an electron, which turns a neutron into a proton. Above we just mentioned the emission of a helium nucleus. Another way of breaking up a nucleus is called electron capture. Normally a cloud of electrons surrounds a nucleus. The electrons form layers or shells. A uranium nucleus may capture one of the electrons from the innermost electron shell. The captured electron combines with a proton to make a neutron. That turns uranium into protactinium, an unstable element having a nucleus with 91 protons.
Eventually, through any of several series of unstable nuclei and various kinds of emissions or captures, uranium disintegrates into lead. Lead has 82 protons and 126 neutrons in its most abundant form. This form of lead is stable. Many alchemists have wished it were not stable. If lead lost three more protons and eight more neutrons it would become gold.
Making the Rest of the Elements
Our Sun is a star, but it is not the earliest type of star. The three elements of the lowest weight, namely, hydrogen, helium, and lithium, were the only elements available to make up the first stars. Three elements were more than enough to serve as fuel for the first stars. Stellar combustion can start with pure hydrogen. The first stars burned bluish-white. They were very hot, and produced more ultraviolet light than visible light. This is because they had to reach a very high temperature through gravitational collapse before they could ignite the hydrogen. Deep in their interiors the three elements were under high pressure, bathed in light and heat.
At the beginning of the universe sufficient heat and pressure for nuclear reactions lasted about three minutes, but in stellar interiors the heat and pressure lasted for millions or thousands of millions of years. During all this time the nuclei were colliding. Occasionally they stuck to one another. The remaining 88 elements had time to form as clumps of the lighter ones.
Carbon nuclei formed, with six protons and six neutrons in each. Complex molecules of carbon and hydrogen are the raw material of all life on Earth. Without oxygen (8 protons and 8 neutrons) we could not breathe. Iron (26 protons and 30 neutrons) is indispensable to the red blood cells for transporting oxygen to all parts of our bodies. All 92 natural elements are needed to make our life possible. The heaviest element, uranium, is necessary to produce an uneven distribution of heat in the center of the Earth. Heat raises the mountains and continents and leaves other, lower places to be the ocean basins.
All the elements “simmered” slowly, at temperatures of millions of degrees, in the centers of massive stars, while the stars burned their fuel, hydrogen. When the nuclei were fully cooked they remained at the bottom of the cauldrons at high temperature and pressure. How could the elements get out and form a habitable planet? The outer layers of the stars acted like pot lids, covering the nuclear soup. Something had to ladle the soup out into individual servings that could nourish and sustain life.
Big nuclei have a number of ways of breaking up. We have discussed the emission or breaking away of an electron, which turns a neutron into a proton. Above we just mentioned the emission of a helium nucleus. Another way of breaking up a nucleus is called electron capture. Normally a cloud of electrons surrounds a nucleus. The electrons form layers or shells. A uranium nucleus may capture one of the electrons from the innermost electron shell. The captured electron combines with a proton to make a neutron. That turns uranium into protactinium, an unstable element having a nucleus with 91 protons.
Eventually, through any of several series of unstable nuclei and various kinds of emissions or captures, uranium disintegrates into lead. Lead has 82 protons and 126 neutrons in its most abundant form. This form of lead is stable. Many alchemists have wished it were not stable. If lead lost three more protons and eight more neutrons it would become gold.
Making the Rest of the Elements
Our Sun is a star, but it is not the earliest type of star. The three elements of the lowest weight, namely, hydrogen, helium, and lithium, were the only elements available to make up the first stars. Three elements were more than enough to serve as fuel for the first stars. Stellar combustion can start with pure hydrogen. The first stars burned bluish-white. They were very hot, and produced more ultraviolet light than visible light. This is because they had to reach a very high temperature through gravitational collapse before they could ignite the hydrogen. Deep in their interiors the three elements were under high pressure, bathed in light and heat.
At the beginning of the universe sufficient heat and pressure for nuclear reactions lasted about three minutes, but in stellar interiors the heat and pressure lasted for millions or thousands of millions of years. During all this time the nuclei were colliding. Occasionally they stuck to one another. The remaining 88 elements had time to form as clumps of the lighter ones.
Carbon nuclei formed, with six protons and six neutrons in each. Complex molecules of carbon and hydrogen are the raw material of all life on Earth. Without oxygen (8 protons and 8 neutrons) we could not breathe. Iron (26 protons and 30 neutrons) is indispensable to the red blood cells for transporting oxygen to all parts of our bodies. All 92 natural elements are needed to make our life possible. The heaviest element, uranium, is necessary to produce an uneven distribution of heat in the center of the Earth. Heat raises the mountains and continents and leaves other, lower places to be the ocean basins.
All the elements “simmered” slowly, at temperatures of millions of degrees, in the centers of massive stars, while the stars burned their fuel, hydrogen. When the nuclei were fully cooked they remained at the bottom of the cauldrons at high temperature and pressure. How could the elements get out and form a habitable planet? The outer layers of the stars acted like pot lids, covering the nuclear soup. Something had to ladle the soup out into individual servings that could nourish and sustain life.