The hell bomb

by William L. Laurence

Since each loss of mass manifests itself by the release of energy, it can be seen that to obtain energy from the atom’s nucleus requires either the fusion of two elements in the first half of the periodic table or the fission of an element in the second half. From a practical point of view, however, fusion is possible only with two isotopes (twins) of hydrogen, at the beginning of the periodic table, while fission is possible only with twins of uranium, U-233 and U-235, and with plutonium, at the lower end of the table.

The diameter of the atom is 100,000 times greater than the diameter of the nucleus. This means that the atom is mostly empty space, the volume of the atom being 500,000 billion times the volume of the nucleus. It can thus be seen that most of the matter in the universe is concentrated in the nuclei of the atoms. The density of matter in the nucleus is such that a dime would weigh 600 million tons if its atoms were as tightly packed as are the protons and neutrons in the nucleus.

The atoms of the elements (of which there are ninety-two in nature, and six more man-made elements) have twins, triplets, quadruplets, etc., known as isotopes. The nuclei of these twins all contain the same number of protons and hence all have the same chemical properties. They differ, however, in the number of neutrons in their nuclei and hence have different atomic weights. For example, an ordinary hydrogen atom has a nucleus of one proton. The isotope of hydrogen, deuterium, has one proton plus one neutron in its nucleus. It is thus twice as heavy as ordinary hydrogen. The second hydrogen isotope, tritium, has one proton and two neutrons in its nucleus and hence an atomic mass of three. On the other hand, a nucleus containing two protons and one neutron is no longer hydrogen but helium, also of atomic mass three.

There are hundreds of isotopes, some occurring in nature, others produced artificially by shooting atomic bullets, such as neutrons, into the nuclei of the atoms of various elements. A natural isotope of uranium, the ninety-second and last of the natural elements, contains 92 protons and 143 neutrons in its nucleus, hence its name U-235, one of the two atomic-bomb elements. The most common isotope of uranium has 92 protons and 146 neutrons in its nucleus and hence is known as U-238. It is 140 times more plentiful than U-235, but cannot be used for the release of atomic energy.

Atomic, or rather nuclear, energy is the cosmic force that binds together the protons and the neutrons in the nucleus. It is a force millions of times greater than the electrical repulsion force existing in the nucleus because of the fact that the protons all have like charges. This force, known as the coulomb force, is tremendous, varying inversely as the square of the distance separating the positively charged particles. Professor Frederick Soddy, the noted English physicist, has figured out that two grams (less than the weight of a dime) of protons placed at the opposite poles of the earth would repel each other with a force of twenty-six tons. Yet the nuclear force is millions of times greater than the coulomb force. This force acts as the cosmic cement that holds the material universe together and is responsible for the great density of matter in the nucleus.

We as yet know very little about the basic nature of this force, but we can measure its magnitude by a famous mathematical equation originally presented by Dr. Einstein in his special theory of relativity in 1905. This formula, one of the great intellectual achievements of man, together with the discovery of the radioactive elements by Henri Becquerel and Pierre and Marie Curie, provided the original clues as well as the key to the discovery and the harnessing of nuclear energy.

Einstein’s formula, E = mc², revealed that matter and energy are two different manifestations of one and the same cosmic entity, instead of being two different entities, as had been generally believed. It led to the revolutionary concept that matter, instead of being immutable, was energy in a frozen state, while, conversely, energy was matter in a fluid state. The equation revealed that any one gram of matter was the equivalent in ergs (small units of energy) to the square of the velocity of light in centimeters per second—namely, 900 billion billion ergs. In more familiar terms, this means that one gram of matter represents 25,000,000 kilowatt-hours of energy in the frozen state. This equals the energy liberated in the burning of three billion grams (three thousand tons) of coal.

The liberation of energy in any form, chemical, electrical, or nuclear, involves the loss of an equivalent amount of mass, in accordance with the Einstein formula. When 3,000 metric tons of coal are burned to ashes, the residual ashes and the gaseous products weigh one gram less than 3,000 tons; that is, one three-billionth part of the original mass will have been converted into energy. The same is true with the liberation of nuclear energy by the splitting or fusing (as will be explained later) of the nuclei of certain elements. The difference is merely that of magnitude. In the liberation of chemical energy by the burning of coal, the energy comes from a very small loss of mass resulting from the rearrangement of electrons on the surface of the atoms. The nucleus of the coal atoms is not involved in any way, remaining exactly the same as before. The amount of mass lost by the surface electrons is one thirtieth of one millionth of one per cent.

On the other hand, nuclear energy involves vital changes in the atomic nucleus itself, with a consequent loss of as high as one tenth to nearly eight tenths of one per cent in the original mass of the nuclei. This means that from one to nearly eight grams per thousand grams are liberated in the form of energy, as compared with only one gram in three billion grams liberated in the burning of coal. In other words, the amount of nuclear energy liberated in the transmutation of atomic nuclei is from 3,000,000 to 24,000,000 times as great as the chemical energy released by the burning of an equal amount of coal. In terms of TNT the figure is seven times greater than for coal, as the energy from TNT, while liberated at an explosive rate, is about one seventh the total energy content for an equivalent amount of coal. This means that the nuclear energy from one kilogram of uranium 235, or plutonium, when released at an explosive rate, is equal to the explosion of twenty thousand tons of TNT.

Nuclear energy can be utilized by two diametrically opposed methods. One is fission—the splitting of the nuclei of the heaviest chemical elements into two uneven fragments consisting of nuclei of two lighter elements. The other is fusion—combining, or fusing, two nuclei of the lightest elements into one nucleus of a heavier element. In both methods the resulting elements are lighter than the original nuclei. The loss of mass in each case manifests itself in the release of enormous amounts of nuclear energy.