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Any alteration of the contents of an atomic nucleus is a nuclear reaction. The nucleus of a hydrogen atom is a proton. The structure of a proton is that of a core surrounded by a cloud of bit pairs. The core is an aggregate of particles, each of which has a positive electrical charge. Whereas like charges repel each other when they are about a centimeter apart, when the positive subparticles, (pos bits), are forced to get much closer to each other, the repulsive force disappears, and there is an attractive force. In other words, there is a boundary. Any pos bit that is inside the boundary is attracted. Any pos bit that is outside the boundary is repelled. Energy is an abstraction. The real thing that it describes is a bit (pos bit or neg bit). A bit that is in the core of the proton has the potential of being forced out of the core and being repelled. When that happens, the bit is accelerated, and flies away at great speed. The single bit moving at that speed has a natural kinetic energy of 1. Before this bit left its home in the core, it had a potential energy of 1. That potential energy is converted into kinetic energy when triggered. The way to trigger the dismantling of the structure of the core of a proton is to force two protons to collide. Because the force of repulsion between proton cores, the cores never acheive contact with each other. Instead, the core of the proton under attack is put into motion and it is torn away from the cloud that surrounds it. The so-called cloud consists of pairs of bits, one positive, one negative. The number of bits in the cloud is much greater than the number of bits in the core. Being neutral, the pairs are not repelled, and they remain unmoved while the core is driven off. The separated core of a proton is called a positron. The core moves away from its source and is attracted to the first electron that it encounters. When the positron interacts with the electron, the attraction between pos bits of the positron and the neg bits of the electron dismantles both cores, and the neg-pos pairs rearrange themselves and emit neg-pos pairs, one pair behind the other in a formation that constitutes a photon in the range of gamma rays. Notice that no change in the number of bits has taken place. That means that the mass of the system has not changed. Mass is the measure of the number of bits in a particle of matter, or in a body of matter. Energy is another measure of the same number of the same bits. The energy of one bit is 1. The mass of one bit is 1. In the entire proton-proton reaction, there is no change in the numbers. The only change is in the fraction of bits that are moving. The rest are standing still. When one particle pushes another particle, it transfers neg-pos pairs to the particle that is gaining motion. When pos bits are concentrated into one core, the bits are not moving, but they have potential energy. When the core is dismantled, its potential energy becomes kinetic energy, but the count of bits remains unchanged. The energy of the system is unchanged. Mass is conserved and energy is conserved. So what is nuclear energy? It is the measure of the change of potential energy into kinetic energy. Confusion arises when we convert the count of bits into conventional units: grams for mass, and ergs for energy. 1.852 x 10-39 gram = mass of 1 bit = 1.667 x 10-18 erg = energy of 1 bit A more serious source of confusion is the equation, E = mC2. It does not mean that mass turns into energy. It means that if you multiply the number of grams in a bit by C2 , you get the number of ergs in a bit. You can convert, mathematically, grams into ergs because they are measures of the same physical object. However you cannot convert matter, which is physical, into energy, which is abstract. Matter is the stuff we observe. Energy is a description of what the stuff is doing or capable of doing. Don't add cherries and apples. The hydrogen bomb converts the potential energy that is in the core of the protons and electrons of hydrogen atoms, into kinetic energy of the motion of the products of the reaction. In order to trigger the reaction, one must accelerate the hydrogen atoms sufficiently. Therefore the bomb is built in two layers, one of which is a uranium bomb, which acts as a trigger. The actual fuel is heavy hydrogen, deuterium. The fact that the bomb works is proof that the reaction has converted potential energy into kinetic energy. Deuterium exists in nature, and can be found in water as a very small fraction. It can be produced with great difficulty in a particle accelerator, in which protons meet head-on. If we ignore the triggering mechanism, we can calculate, in the fashion of chemists, the mass of the reactants and the mass of the products. Subtract the charge of the products from the charge of the reactants: 3.344876 x 10-24 gm minus 3.344034 x 10-24 gm equals 7.532 x 10-28 gm There is a shortage of 7.532 x 10-28 gm of mass. I can account for the missing mass. When a positron is not in motion, it has a mass of 9.1083 x 10-28 grams. A moving positron has additional mass which it had absorbed during its acceleration. This reaction is very mild compared with other nuclear reactions which are often 50 times as energetic than the proton conversion to deuteron. The nucleus of the atom of heavy hydrogen , or deuterium, is called a deuteron. There is a reaction between a deuteron and a proton, which produces a light helium nucleus, which has only one neutron and two protons. The missing mass is carried off by a gamma ray. The mass that is transferred in the reaction is 9.7625 x 10-27 grams. Light helium is called helium 3 because it contains 3 particles in its nucleus, or 3 nucleons. The proton plus deuteron to helium 3 reaction is 13 times as energetic as the proton to deuterium reaction. Thirteen times as much mass is transferred. In another reaction, two helium 3 nuclei react and form a helium 4 nucleus and two free protons. The missing mass departs with the protons. The total mass that is transferred is more than twice the mass transferred in the reaction that produces helium 3. All three of the reactions which I have just described presumably take place in the sun and the stars. Attempts are being made to build a reactor for that kind of reaction in order to produce electricity. The biggest problem is to invent a container that can hold matter at temperatures in the millions of degrees. Reactions of this kind occur during the explosion of a hydrogen bomb. The last word has not yet been said about the possibility of producing these reactions under milder conditions. By analogy with chemical reactions, a proton and a neutron bind to each other and yield the binding energy to the environment. Two protons and two neutrons bind more strongly and yield more energy together than two sets of separate proton-neutron systems. The elements listed from hydrogen to calcium progress from one proton in the nucleus to twenty protons in the nucleus. Most of these nuclei contain the same number of neutrons as protons. In general, the higher the number of protons, the stronger the binding energy between one proton and one neutron. The climax of this progression is reached at iron, with 26 protons. Nuclei with more than 26 protons progress toward weaker binding energy per nucleon as the number of protons increases. Furthermore, the number of neutrons grows faster than the number of protons. Uranium, with 92 protons, has 146 neutrons. It has a total of 238 nucleons. That makes it uranium 238 . The binding energy per nucleon is as low for uranium 238 as for carbon 12. Uranium is unstable although carbon 12 , and all of the other light elements, are quite stable. Besides having a low binding energy per nucleon, uranium has many nucleons. It has a large deficit of total binding energy. 238 nucleons with a binding energy deficit are much less stable than 12 nucleons with a similar binding energy deficit per nucleon. From another point of view, nuclei with lower binding energy per nucleon have higher mass per nucleon. Associated with higher mass is higher potential energy. A large nucleus, like the nucleus of uranium 238, has a lot of potential energy. There is some mutual transfer of potential energy between the nucleons within the uranium nucleus. Occasionally, one neutron or proton is burdened with more potential energy than the others. That nucleon can emit a photon or leave the nucleus itself. This makes radioactivity possible. Uranium238 does not lose a lone proton or neutron. It loses a helium nucleus. The loss of four nucleons reduces the number of nucleons to 234. The number of protons is reduced from 92 to 90. The product nucleus is thorium 234. Thorium 234 decays by losing an electron from the nucleus. The nucleus does not contain any electrons to begin with. One of the neutrons breaks apart and radiates 9.108 x 10-28 gm of neg along with some neg-pos. That constitutes an electron with a lot of kinetic energy. The odd thing about this disintegration is that the nucleon count remains the same, but the proton count goes up one unit. The product is protactinium 234. It has 91 protons because one neutron gives up an electron and becomes a proton. A neutron is equally neg and pos in the form of neg-pos. A proton, which is neg-pos except for 9.108 x 10-28 gm of pos, can lose the 9.108 x 10-28 gm of pos as a positron, and become a neutron with only neg-pos. Nucleons have varying quantities of neg-pos corresponding to their potential energies. A proton in a lead nucleus has more neg-pos than a proton in an iron nucleus. The only fixed value of mass for a proton is for a free proton , far from all forces, and not in motion. Step by step, uranium changes its number of nucleons and its identity as an atomic nucleus. After 18 transformations, uranium changes into lead 206, which is stable. At every step, the remaining nucleons have less neg-pos charge, and less potential energy than at the preceding step. Since mass departs with each of these nuclear processes, the mass of the remaining nucleus is always less than that of the previous nucleus. If one sees the mass departing, and doesn't see where it arrives, one gets the notion that the mass ceases to exist. Mass never goes out of existence. Matter is always conseved. When gamma rays were first discovered, it was thought that a gamma ray had no mass. Energy departing on a massless gamma ray made it appear that mass is converted into energy. But the gamma ray does have mass. Matter cannot possibly change into energy. There is a nuclear reaction between lithium 7 and a proton. It produces two helium 4 nuclei. Textbooks give this accounting: |
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Find the sum of the reactants and the sum of the products. Subtract one sum from the other. |
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The difference of 3 x 10-26 grams looks like a loss of mass. The error is in the use of the mass of resting helium, instead of helium in motion. The energy of the reaction resides in the moving helium atoms. Therefore the mass of the helium atoms must be their mass when moving. In that way it is discovered that there is no loss of mass. When the helium atoms arrive at the end of their journey, they yield mass to whatever they collide with, along with energy. With all of the nuclear reactions yielding energy to the environment, it would appear that eventually the only element left in the universe would be iron, and all activity would cease. It happens that there are wrong-way reactions in nuclear physics, just as there are wrong-way reactions in chemistry. One way to get a reverse reaction is by linking a right-way reaction with a wrong-way reaction. Another way is to let a very energetic particle collide with a stable nucleus. One example of a wrong-way nuclear reaction is the high-speed collision between a helium nucleus and a nitrogen nucleus: helium 4 + nitrogen 14 -----> oxygen 17 + proton The total mass of the products is greater than the total mass of the reactants at rest. The extra mass arrives on the fast-moving helium nucleus. Even allowing for wrong-way reactions, there is no assurance that the universe is not heading toward a standstill. The best assurance that the universe has no doom awaitng it, is the limited extent of our knowledge. We don't know enough about the universe to make any rules or offer prophesies. Neutrons have a special place in nuclear reactions because they are not repelled like protons by a positively charged nucleus. Neutrons are often admitted into nuclei, when the excess mass is radiated as gamma rays. In cases in which nothing is radiated, the neutron rebounds. The rebound is due to a very close-range force that prevents neutrons from merging with other nuclear particles into one big blob of bits. Some nuclei absorb more low energy neutrons. The absorption of neutrons is responsible for some nuclear fission. Fission is the breaking of a nucleus into pieces that are larger than helium nuclei. Some nuclei divide spontaneously. Some nuclei undergo fission when they receive high energy protons, helium nuclei, gamma rays, or deuterons. In addition to the product nuclei, fission usually produces small particles with high energies, including neutrons. There are three materials which are highly fissionable, uranium 235, uranium 233, and plutonium 239. Many other nuclei are fissionable, but are not reliable reactor fuels. They do not always split. They sometimes get rid of excess mass by emitting photons or other simple products. Even the three highly fissionable nuclei sometimes radiate small particles instead of splitting. Fission can be started by the absorption of low energy or high energy neutrons. Some nuclei respond better to a particular level of neutron energy. The fission producers are nuclei of intermediate size. They all have too many neutrons. Ordinarily, the nuclei of the largest elements have a high ratio of neutrons to protons. When all of those neutrons are divided between two intermediate nuclei, they are excessive. As a result, a neutron emits an electron and becomes a proton. That reduces the ratio of neutrons to protons. For example, one fission product is xenon 140, with 54 protons. The xenon 140 nucleus emits an electron and becomes cesium 140, with 55 protons. Next, the cesium 140 ejects an electron and turns into barium 140 , with 56 protons. By dropping an electron, barium 140 becomes lanthanum 140, with 57 protons. Finally, losing an electron, lanthanum 140 becomes cerium 140 , with 58 protons, and the nucleus is stable. Immediately upon breaking apart, the fission products eject some of their excess meutrons. In the example of xenon 140, the nucleus probably starts out as xenon 145. Immediately 5 neutrons depart. The xenon 140 then starts to lose one electron at a time and become a succession of different elements. The five, or so, neutrons can either escape to the environment, becoming part of another nucleus by emitting a photon, or initiate fission in another uranium nucleus. If enough neutrons contribute to additional fission reactions, there is a chain reaction. If the amount of starting material is small, neutrons escape more easily into the environment. If the amount of starting material is large, neutrons are captured by uranium nuclei before they can escape. When the amount of starting material exceeds the critical size, there is a nuclear explosion. A nuclear reactor which produces steam to run an electric generator, has a system for controlling the density of the starting material and the speed of the neutrons. In that way, the chain reaction is made to proceed at a safe slow rate if nothing goes wrong. The textbook version of nuclear energy depicts a repulsive force between two protons, which increases as the protons approach each other. When the force is at a maximum, it suddenly falls to zero. The force is cancelled by an equally strong attractive force, which increases as the protons get still closer together. The repulsive force between protons is called the weak force, and the attractive force at short range is called the strong force. It would be nice if they would explain the existence of two different forces. Consider this: everything is made of neg bits and pos bits. The behavior of anything larger than a single bit is due entirely to the way bits behave. Bits do not change their character when they combine. The core of a proton is an aggregate of 4.94 x 1020 pos bits. There are 1800 times as many bits in the rest of the proton. The neg-pos pairs surround the positive core, and they orient themselves with the neg bit facing the core and the pos bit facing away from the core. It presents a skin of pos bits to the outside world. When two protons are pushed toward each other, The neg-pos pairs on one proton get turned around because of the attraction between opposite charges. At that instant, the cores of both protons move to the far side of their proton. If the protons are forced a trifle closer than that, one core escapes. The core is then a positron, and the residue is a neutron. A positron carries, along with the core, a cortege of neg-pos bits whose number is consistent with the speed of the positron as it flies away. Those neg-pos bits account for what is called the missing mass. When the mass of a positron is measured, it is not moving with the speed it had when it left the proton. The point that I am making is that there is no strong force. The force that binds the nucleons is the same force that binds a neg bit to a pos bit in neg-pos. It has strength because it involves many zillions of bits. Incidentally, neutrons come in two sizes. The free neutron contains a pos core plus a neg core. That is a heavy neutron. When it loses a neg core, it becomes a proton. When the proton loses a pos core, it becomes a light neutron, which has no core at all. |
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