Nuclear fission
Nuclear fission is a process where the nucleus of an atom, typically uranium-235 (U-235), is split into smaller nuclei upon absorbing a neutron, resulting in a release of a significant amount of energy. This reaction is harnessed for two primary purposes: electricity generation and the development of nuclear weapons. The concept of nuclear fission was first realized in 1938 by scientists Otto Hahn, Lise Meitner, and others, leading to groundbreaking applications that have shaped modern energy production and military technology.
The energy released in fission reactions, approximately 200 mega-electron volts per event, is vastly greater than that from typical chemical reactions, making nuclear power a potent energy source. For instance, one kilogram of U-235 can yield energy equivalent to about 3,000 tons of coal. Key developments, such as the first self-sustaining nuclear chain reaction achieved by Enrico Fermi in 1942 and the atomic bombings of Hiroshima and Nagasaki in 1945, underscore the dual-use nature of this technology.
As the world grapples with the implications of nuclear fission, concerns about its use for weapons proliferation, particularly in nations pursuing enrichment processes, remain a significant issue in international relations. Enrichment involves increasing the concentration of U-235, a process that is challenging and technically complex, with various methods, including gas centrifugation and newer techniques like SILEX. As technology advances, new applications for nuclear fission continue to emerge, such as nuclear batteries that could provide long-term power without maintenance.
Nuclear fission
Summary: Nuclear fission is used in electricity production and weaponry. This makes it a disputable technology that many countries, including some rogue nations, would like to master.
In 1938, Otto Hahn, Lise Meitner, Fritz Strassmann, and Otto Frisch produced smaller nuclei by bombarding uranium (U-235) with neutrons. This process is called nuclear fission because it resembles biological fission, wherein cells divide to produce new cells. Hahn, a German scientist, received the 1944 Nobel Prize in Chemistry for this work.
Neutrons have no charge and are more effective in breaking nuclei than are protons. The following is a typical nuclear fission reaction:
1n + 235U g 236U g 142Ba + 91Kr + 3 1n.
Nuclei consist of neutrons and protons, commonly called nucleons. The total mass of all individual nucleons in a nucleus is more than the mass of the nucleus. This difference is the result of a loss of mass due to binding energy, which is released during the formation of the nucleus. This energy conversion of mass follows Albert Einstein’s equation, E = mc2, where E is the energy equivalent of mass, m, and c is the speed of light. This binding energy, if supplied to the nucleus, can break it into protons and neutrons.
In a fission process, there is an increase in the binding energy/nucleon in going from parent nuclei to daughter nuclei. This increase in binding energy is released in the form of energy and is about 200 mega-electron volts for U-235. This energy is about a million times higher than the energy from chemical reactions, such as the burning of gasoline or TNT. Currently, this enormous energy is mostly used for two purposes: in electricity generation and in weaponry.
One kilogram of U-235 has about 2.6 × 1024 nuclei. In the case of complete fission, it provides 8 × 1010 British thermal units (Btu) of energy. To supply an amount of energy comparable to 1 kilogram of U-235 using conventional energy resources would, for example, require 3,000 tons of coal or 14,000 barrels of oil to produce energy. Also, while a nuclear power plant requires the shipment of fuel once every year, a comparable coal-fired plant may require one trainload of coal every day.
Polonium and lithium are combined to produce a burst of neutrons that are employed in fission. Polonium-210 is a radioactive substance, with a half-life of 138.376 days, and serves as a source of alpha particles. Lithium reacts with alpha particles to produce neutrons.
Albert Einstein sent a letter to President Franklin D. Roosevelt on August 2, 1939, asking him to sanction a project to make a nuclear-fission bomb. He wrote: “… it may become possible to set up a nuclear chain reaction in a large mass of uranium, by which vast amounts of power and large quantities of new radium-like elements would be generated. … This new phenomenon would also lead to the construction of bombs, and it is conceivable—though much less certain—that extremely powerful bombs of a new type may thus be constructed. A single bomb of this type, carried by boat and exploded in a port, might very well destroy the whole port together with some of the surrounding territory.”
The and the Atom Bomb
Einstein’s letter convinced President Roosevelt, eventually leading to the Manhattan Project, which resulted in the construction of the first nuclear fission (atom) bombs, detonated over Japan in the summer of 1945 and effectively ending World War II in the Pacific.
The first self-sustaining nuclear fission chain reaction was achieved in 1942 under the direction of Enrico Fermi, an immigrant Italian scientist at the University of Chicago. Fermi received the Nobel Prize in 1938 and went to Stockholm to participate in the ceremonies.
Nuclear Fission of Uranium 235
Because his wife was a Jew and anti-Semitic atrocities had already been promulgated in the lead-up to World War II, he was concerned about her safety in Italy. He therefore opted to immigrate to America after the festivities. As a result, he would contribute his expertise to those of American scientists in expediting their quest for a chain reaction. After the successful test, a secret message was sent to Washington: “The Italian navigator has landed in the New World and found the natives very friendly.”
The growth of neutrons in successive fission is geometric if there is no loss of neutrons to the environment. This geometric growth of the reaction rate leads to an explosive release of energy. The first atom bomb was dropped on Hiroshima, Japan, in August 1945. This bomb used almost pure uranium, while the bomb that was dropped a few days later on Nagasaki used plutonium. Both bombs were based on the principle of nuclear fission.
The energy produced by nuclear fission would soon find multiple other uses. In 1951, electricity was first generated from a nuclear reactor, called the Experimental Breeder Reactor (EBR), in Idaho. In 1953, the nuclear-powered submarine Nautilus was built, launching the following January. In 1957, in Shippingport, Pennsylvania, the first commercial reactor for electricity production became operational.
The uranium ores available in nature contain only about 0.7 percent uranium-235. Most of it is in the form of U-238. To increase the probability of fission in a nuclear reactor, natural uranium must be “enriched” to increase the concentration of U-235 to a level of 2 to 4 percent, using diffusion or centrifugation. However, a concentration of about 95 percent or more of U-235 is needed for making a deadly nuclear bomb. Enrichment of uranium is not an easy task, and only a handful of countries have achieved it.
It is much easier to produce plutonium, as one can separate it using chemical techniques. However, the design for nuclear fission is fairly complicated for plutonium; it requires an implosion to increase the density of plutonium before it explodes. This, too, is not an easy task. Most nuclear power plants produce plutonium because the U-238 in the fuel rods fissions into plutonium. However, most countries do not reprocess the nuclear waste to extract the plutonium. It is done to improve accountability of the radioactive materials for safety reasons.
Using neutron reflectors, one can construct a plutonium-239 bomb with only 11 pounds (5 kilograms) of material. Similarly, with only 33 pounds (15 kilograms), one can achieve a self-sustained chain reaction with uranium-235. The minimum amount of mass needed for a self-sustained reaction is called the critical mass.
The Enrichment Process
The most difficult component in achieving self-sustained fission is the acquirement of enriched uranium. While plutonium can be separated chemically, it is not possible to isolate uranium-235 from uranium-238 chemically, since both isotopes have the same chemical properties. The most common process to enrich uranium uses a gas centrifuge, which works much like a centrifuge used in a chemistry laboratory. However, a centrifuge to separate uranium isotopes spins with ultrahigh speed, comparable to the speed of sound and much faster than a classic centrifuge. Uranium hexafluoride gas is injected into the centrifuge, which spins and separates different isotopes based on weight.
Separation of isotopes using a centrifuge was accomplished for elements with small atomic numbers in 1934 by Jesse Beams of the University of Virginia. The ultrahigh speed to separate uranium isotopes was achieved with the help of Gernot Zippe, an Austrian scientist, at the University of Virginia using a magnetic field. This separation process uses a large number of centrifuges in succession. A common problem is the condensation of uranium hexafluoride (UF6) on the rotor, which upsets the balance and causes the assembly to crash.
Achieving Purity
Enriching uranium is a slow and cumbersome process. However, as the concentration of U-235 increases, it becomes easier to purify it further. In other words, it is a lot more difficult to achieve 20 percent purity of U-235 from 0.7 percent purity found in uranium ore than to achieve 40 percent enrichment from a 20 percent enriched uranium sample. This fact is currently causing great concern to the world community, particularly as it attempts to monitor the enrichment process occurring in Iran. Iran claims to be enriching uranium for energy production (use in their nuclear power plants). However, some countries are concerned that further enrichment could make it possible for Iran to acquire bomb-level uranium, and some nations are concerned that Iran is deliberately seeking to achieve that goal.
A new, highly classified laser excitation technique, known as SILEX, is being used to enrich uranium. SILEX (an acronym for the separation of isotopes by laser excitation) uses a tuned laser of a particular frequency to bombard uranium ore. Lasers at this particular frequency can ionize U-235 selectively, with high precision. The ionized uranium is collected using conventional charged plates. This process is easier to achieve and consumes much less energy than the conventional gas centrifuge.
New Applications
In January 2024, a Chinese company announced it had created a nuclear battery that could provide power for fifty years without requiring maintenance or recharging. Betavolt relied on nickel-63 isotopes in a module smaller than a coin. The company cited cellphones and drones as potential uses for the nuclear batteries, which were being tested.
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