Chain reaction
A chain reaction is a process where one change triggers subsequent changes, leading to a series of events. While the concept can apply to various fields, it is most notably associated with chemistry and physics, particularly in the context of atomic interactions. In chemistry, a chain reaction begins with initiation, where reactive molecules are formed; follows with propagation, where these active particles create more reactants; and concludes with termination, where inactive particles are produced, halting the reaction. Nuclear chain reactions, characterized by their high energy output, involve processes like nuclear fission, where heavy atoms such as uranium are split to release energy. The first successful nuclear chain reaction was achieved in 1942, marking a significant milestone with profound implications for energy production and military capabilities during World War II. Beyond weaponry, chain reactions play a vital role in modern science, exemplified by techniques like polymerase chain reaction (PCR) used in DNA manipulation. This method has revolutionized fields such as forensics and genetic research, showcasing the broader impact of chain reactions across disciplines.
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Chain reaction
A chain reaction describes the event when one change directly causes additional changes. The term is used to describe anything from a series of decisions to economic events to weather patterns, but it is primarily associated with chemistry and physics. These chain reactions depend on the activity of atoms. Different atoms can bond together, forming molecules. Outside stimuli can both forge and break bonds, creating chemical reactions. Many chemical reactions create conditions among molecules that incite further reactions, producing exponentially more energy with only the first requiring outside influence.
Most chain reactions consist of three steps: initiation, propagation, and termination. Initiation involves the creation of molecules with the potential to undergo reaction. In propagation, the active particles create more active particles. In termination, a reaction creates inactive particles, bringing the chain reaction to an end.
One of the most prominent types of chain reaction is the nuclear chain reaction. Nuclear reactions have an extremely high energy yield because they involve atoms that are energized with radiation. The discovery of the nuclear chain reaction was essential to the creation of nuclear plants and weapons.
Brief History
In 1913, German chemist Max Bodenstein proposed the concept of chemical chain reactions. He theorized that the reactions of certain molecules would produce more molecules that had the potential to undergo further reactions. Chemist Walther Nernst made another breakthrough in 1918 when he identified light as the stimulus for reactions involving hydrogen and chlorine atoms.
Scientists Christian Christiansen and Hendrik Kramers, collaborating in 1923, discovered that there were other ways to initiate chain reactions. They found that molecules could naturally collide, both creating and breaking bonds, and forming unstable molecules ready to undergo subsequent reactions. They also realized that this process was chaotic enough that it would not only produce a single, linear chain reaction. With enough unstable molecules produced, one reaction could lead to several, separate chain reactions.
The concept of chain reactions was first applied to radioactive matter in the early 1930s. It had been known since the late nineteenth century that certain atoms were radioactive, which meant they could ionize, or energize, atoms by emitting particles. Knowledge of the atom increased drastically in 1932, when James Chadwick discovered the neutron, which, along with protons and electrons, make up an atom.
In 1933, Hungarian scientist Leo Szilard realized that neutrons offered many new possibilities for chain reaction. Scientists had discovered that they could induce reactions by smashing accelerated protons into atoms, but Szilard envisioned using neutrons in a similar way. However, he was not able to identify an element that could produce the results for which he was looking.
Several different laboratories were continuing to study radioactive elements and the possibility of producing nuclear reactions. A Berlin laboratory with scientists Otto Hahn, Fritz Strassmann, Lise Meitner, and Otto Frisch made a breakthrough in late 1938. The scientists discovered a process that would be known as nuclear fission. They could split atoms of the element uranium. As one of the heaviest elements accessible on Earth, uranium's atoms typically contained more neutrons than most others did. Once Szilard learned of the experiments, he realized that uranium was a strong candidate for a fission chain reaction and teamed with scientist Enrico Fermi to attempt to create one.
Impact
Once scientists accepted the theory of a nuclear chain reaction, global interest saw a dramatic increase. The discovery was made during World War II (1939–1945), and the global powers dedicated significant resources to studying the potential of nuclear chain reactions.
On December 2, 1942, the Fermi-led US team produced the first successful nuclear chain reaction. This experiment demonstrated nuclear power's great potential as both an energy resource and a weapon, and it immediately changed how wars were fought. There was a global arms race to develop the first nuclear weapons. In the summer of 1945, the United States successfully tested the first atomic bomb. It made use of the chain reaction's property of releasing exponentially increasing amounts of energy, building up into a blast that contained far more explosive yield than non-nuclear weapons. By this time, war in the European theater had ended, and Japan was the last major Axis power still fighting. The United States dropped two atomic bombs on the Japanese cities of Hiroshima and Nagasaki that August.
Those bombings mark the only times that nuclear weapons have been used in an attack. Once the world could see the massive power of a fission bomb, the race for nuclear power escalated, defining global relations for decades. Following World War II, the United States and the Soviet Union were the most heavily armed, combat-ready nations in the world, and in conflict with each other. Since both possessed the weaponry to cause irreparable damage to the other, they never directly confronted each other in warfare, instead attempting to gain allies and influence among the rest of the world. This notion of refraining from using nuclear weapons because the result would be devastating to all involved was known as mutually assured destruction, and it was a policy that influenced the entire world for the second half of the twentieth century.
Much of that tension decreased when the Soviet Union collapsed in 1991. Even after that time, however, nuclear weapons remain a critical part of global relations in the twenty-first century. Their use becomes a key factor in diplomacy whenever hostilities arise that involve a nation with a nuclear arsenal.
Beyond weaponry, nuclear chain reactions were used to produce power plants. Nuclear power as an energy resource has been controversial since its discovery. Proponents argue that it can provide reliable electricity with relatively little fuel or waste. Detractors point to the risks of reactors leaking or plants exploding.
Chain reactions are critical to chemistry, biology, and physics. They are used to replicate substances at a molecular level. Biologist Kary Mullis pioneered a technique known as polymerase chain reaction (PCR). This is used to manipulate DNA, or deoxyribonucleic acid, the genetic material that determines the traits of living beings. PCR uses DNA's natural function of replicating to target specific segments, causing a chain reaction that increases the copies of that segment. It replicates exponentially, creating a very large amount of DNA from only a trace sample. This has had a major impact on not only science's opportunity to study and manipulate DNA, but also to society in general. The ability to identify an individual even with only small samples has helped with forensics, determining parentage and ancestry, and testing suspects of crimes.
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