Robert Bent, age 12, of Milton, Mass., for his question.
What is an isotope?
An isotope is an atom , a very special kind of atom. There may be an isotope among the trillions of atoms that make up a lump of sugar. There may be a few isotopes in the uncountable number of particles that make up a glass of water. The atomic bomb exploded from a vast concentration of isotopes.
Our world, and everything in it, is made up of about a hundred different kinds of normal atoms. When a material is all made of atoms of one kind we call it an element iron, gold and oxygen are elements. When a material is made of different kinds of atoms we call it a substance or a compound ice cream, wood and water are compounds.
A1l atoms have a central nucleus of one or more protons. An atom of hydrogen has one proton, an atom of oxygen has eight. In addition, most atoms carry a number of neutrons along with the protons in the nucleus. The normal hydrogen atom does not do this, the normal oxygen atom carries eight neutrons along with its eight protons.
Each element has been listed in a table and given a number. The number refers to the protons in the atom s nucleus. Hydrogen is number one on the atomic table, oxygen is number eight. The number of protons in each atom is exactly balanced by the number of electrons which whirl about it. An atom of hydrogen has one electron. An atom of oxygen has eight.
Atoms have also been arranged in a table of weights. The number 18 was chosen for the weight of oxygen. Hydrogen is the lightest, as number one, normal uranium is a heavy atom with a weight of 92.
Once in a while, an atom weighs more, or loss, than it should,
These atoms carry more, or fewer, than their normal number of neutrons. A few of the hydrogen atoms in your lump of sugar or glass of water may be carrying one neutron, when the normal hydrogen atom carries none. A Few oxygen atoms in a breath of air may be carrying nine, or even ten neutrons, instead of the normal eight.
These special atoms are the isotopes. These extra heavy atoms are still elements of hydrogen or oxygen for they still carry only the normal number of protons. Every uranium atom carries 92 protons. The normal uranium atom carries 116 neutrons in the nucleus. Its atomic number is 92, its atomic weight is 238, One isotope of uranium, however, carries only 143 neutrons. Though its number is still 92, its atomic weight goes down to 235. It is the highly explosive material Uranium 235 or U 235 for short.
The lack of neutrons in the large atom tends to make it unstable. When a stray neutron flies into the nucleus, this big atom tends to fly apart. It breaks into two other atoms, elements of barium and kripton. And the energy which bound the particles of the atom together flies off in a terrific explosion. One pound of this exploding isotope can give off as much heat and energy as almost 3 million pounds of burning coal.