File Name: fission and fusion reactions .zip
Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles neutrons or protons. The difference in mass between the reactants and products is manifested as either the release or the absorption of energy. This difference in mass arises due to the difference in atomic binding energy between the nuclei before and after the reaction.
Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles neutrons or protons.
The difference in mass between the reactants and products is manifested as either the release or the absorption of energy. This difference in mass arises due to the difference in atomic binding energy between the nuclei before and after the reaction. Fusion is the process that powers active or main sequence stars and other high-magnitude stars, where large amounts of energy are released.
A fusion process that produces nuclei lighter than iron or nickel will generally release energy. These elements have relatively small mass per nucleon and large binding energy per nucleon.
Fusion of nuclei lighter than these releases energy an exothermic process , while fusion of heavier nuclei results in energy retained by the product nucleons, and the resulting reaction is endothermic. The opposite is true for the reverse process, nuclear fission. This means that the lighter elements, such as hydrogen and helium , are in general more fusible; while the heavier elements, such as uranium , thorium and plutonium , are more fissionable.
The extreme astrophysical event of a supernova can produce enough energy to fuse nuclei into elements heavier than iron. In , Arthur Eddington suggested hydrogen-helium fusion could be the primary source of stellar energy. Quantum tunneling was discovered by Friedrich Hund in , and shortly afterwards Robert Atkinson and Fritz Houtermans used the measured masses of light elements to show that large amounts of energy could be released by fusing small nuclei.
Building on the early experiments in nuclear transmutation by Ernest Rutherford , laboratory fusion of hydrogen isotopes was accomplished by Mark Oliphant in In the remainder of that decade, the theory of the main cycle of nuclear fusion in stars was worked out by Hans Bethe.
Research into fusion for military purposes began in the early s as part of the Manhattan Project. Self-sustaining nuclear fusion was first carried out on 1 November , in the Ivy Mike hydrogen thermonuclear bomb test. Research into developing controlled fusion inside fusion reactors has been ongoing since the s, but the technology is still in its development phase.
The release of energy with the fusion of light elements is due to the interplay of two opposing forces: the nuclear force , which combines together protons and neutrons, and the Coulomb force , which causes protons to repel each other. Protons are positively charged and repel each other by the Coulomb force, but they can nonetheless stick together, demonstrating the existence of another, short-range, force referred to as nuclear attraction.
This is because the nucleus is sufficiently small that all nucleons feel the short-range attractive force at least as strongly as they feel the infinite-range Coulomb repulsion.
Building up nuclei from lighter nuclei by fusion releases the extra energy from the net attraction of particles. For larger nuclei , however, no energy is released, since the nuclear force is short-range and cannot continue to act across longer nuclear length scales.
Thus, energy is not released with the fusion of such nuclei; instead, energy is required as input for such processes. Fusion powers stars and produces virtually all elements in a process called nucleosynthesis. The Sun is a main-sequence star, and, as such, generates its energy by nuclear fusion of hydrogen nuclei into helium.
The fusion of lighter elements in stars releases energy and the mass that always accompanies it. For example, in the fusion of two hydrogen nuclei to form helium, 0. It takes considerable energy to force nuclei to fuse, even those of the lightest element, hydrogen. When accelerated to high enough speeds, nuclei can overcome this electrostatic repulsion and be brought close enough such that the attractive nuclear force is greater than the repulsive Coulomb force.
The strong force grows rapidly once the nuclei are close enough, and the fusing nucleons can essentially "fall" into each other and the result is fusion and net energy produced. The fusion of lighter nuclei, which creates a heavier nucleus and often a free neutron or proton, generally releases more energy than it takes to force the nuclei together; this is an exothermic process that can produce self-sustaining reactions.
Energy released in most nuclear reactions is much larger than in chemical reactions , because the binding energy that holds a nucleus together is greater than the energy that holds electrons to a nucleus.
For example, the ionization energy gained by adding an electron to a hydrogen nucleus is Fusion reactions have an energy density many times greater than nuclear fission ; the reactions produce far greater energy per unit of mass even though individual fission reactions are generally much more energetic than individual fusion ones, which are themselves millions of times more energetic than chemical reactions.
Only direct conversion of mass into energy , such as that caused by the annihilatory collision of matter and antimatter , is more energetic per unit of mass than nuclear fusion. Research into using fusion for the production of electricity has been pursued for over 60 years. Although controlled fusion is generally manageable with current technology e. At present, controlled fusion reactions have been unable to produce break-even self-sustaining controlled fusion.
Workable designs for a toroidal reactor that theoretically will deliver ten times more fusion energy than the amount needed to heat plasma to the required temperatures are in development see ITER. The ITER facility is expected to finish its construction phase in It will start commissioning the reactor that same year and initiate plasma experiments in , but is not expected to begin full deuterium-tritium fusion until Similarly, Canadian-based General Fusion , which is developing a magnetized target fusion nuclear energy system, aims to build its demonstration plant by The US National Ignition Facility , which uses laser-driven inertial confinement fusion , was designed with a goal of break-even fusion; the first large-scale laser target experiments were performed in June and ignition experiments began in early An important fusion process is the stellar nucleosynthesis that powers stars , including the Sun.
In the 20th century, it was recognized that the energy released from nuclear fusion reactions accounts for the longevity of stellar heat and light.
The fusion of nuclei in a star, starting from its initial hydrogen and helium abundance, provides that energy and synthesizes new nuclei. Different reaction chains are involved, depending on the mass of the star and therefore the pressure and temperature in its core.
Around , Arthur Eddington anticipated the discovery and mechanism of nuclear fusion processes in stars, in his paper The Internal Constitution of the Stars. This was a particularly remarkable development since at that time fusion and thermonuclear energy had not yet been discovered, nor even that stars are largely composed of hydrogen see metallicity.
Eddington's paper reasoned that:. The net result is the fusion of four protons into one alpha particle , with the release of two positrons and two neutrinos which changes two of the protons into neutrons , and energy. In heavier stars, the CNO cycle and other processes are more important.
As a star uses up a substantial fraction of its hydrogen, it begins to synthesize heavier elements. The heaviest elements are synthesized by fusion that occurs when a more massive star undergoes a violent supernova at the end of its life, a process known as supernova nucleosynthesis. A substantial energy barrier of electrostatic forces must be overcome before fusion can occur. At large distances, two naked nuclei repel one another because of the repulsive electrostatic force between their positively charged protons.
If two nuclei can be brought close enough together, however, the electrostatic repulsion can be overcome by the quantum effect in which nuclei can tunnel through coulomb forces. When a nucleon such as a proton or neutron is added to a nucleus, the nuclear force attracts it to all the other nucleons of the nucleus if the atom is small enough , but primarily to its immediate neighbours due to the short range of the force. The nucleons in the interior of a nucleus have more neighboring nucleons than those on the surface.
Since smaller nuclei have a larger surface area-to-volume ratio, the binding energy per nucleon due to the nuclear force generally increases with the size of the nucleus but approaches a limiting value corresponding to that of a nucleus with a diameter of about four nucleons.
It is important to keep in mind that nucleons are quantum objects. So, for example, since two neutrons in a nucleus are identical to each other, the goal of distinguishing one from the other, such as which one is in the interior and which is on the surface, is in fact meaningless, and the inclusion of quantum mechanics is therefore necessary for proper calculations.
The electrostatic force, on the other hand, is an inverse-square force , so a proton added to a nucleus will feel an electrostatic repulsion from all the other protons in the nucleus. The electrostatic energy per nucleon due to the electrostatic force thus increases without limit as nuclei atomic number grows.
The net result of the opposing electrostatic and strong nuclear forces is that the binding energy per nucleon generally increases with increasing size, up to the elements iron and nickel , and then decreases for heavier nuclei. Eventually, the binding energy becomes negative and very heavy nuclei all with more than nucleons, corresponding to a diameter of about 6 nucleons are not stable.
The four most tightly bound nuclei, in decreasing order of binding energy per nucleon, are 62 Ni , 58 Fe , 56 Fe , and 60 Ni. This is due to the fact that there is no easy way for stars to create 62 Ni through the alpha process. An exception to this general trend is the helium-4 nucleus, whose binding energy is higher than that of lithium , the next heaviest element. This is because protons and neutrons are fermions , which according to the Pauli exclusion principle cannot exist in the same nucleus in exactly the same state.
Each proton or neutron's energy state in a nucleus can accommodate both a spin up particle and a spin down particle.
Helium-4 has an anomalously large binding energy because its nucleus consists of two protons and two neutrons it is a doubly magic nucleus , so all four of its nucleons can be in the ground state.
Any additional nucleons would have to go into higher energy states. Indeed, the helium-4 nucleus is so tightly bound that it is commonly treated as a single quantum mechanical particle in nuclear physics, namely, the alpha particle.
The situation is similar if two nuclei are brought together. As they approach each other, all the protons in one nucleus repel all the protons in the other. Not until the two nuclei actually come close enough for long enough so the strong nuclear force can take over by way of tunneling is the repulsive electrostatic force overcome. Consequently, even when the final energy state is lower, there is a large energy barrier that must first be overcome. It is called the Coulomb barrier.
The Coulomb barrier is smallest for isotopes of hydrogen, as their nuclei contain only a single positive charge. A diproton is not stable, so neutrons must also be involved, ideally in such a way that a helium nucleus, with its extremely tight binding, is one of the products. Using deuterium—tritium fuel, the resulting energy barrier is about 0. In comparison, the energy needed to remove an electron from hydrogen is The intermediate result of the fusion is an unstable 5 He nucleus, which immediately ejects a neutron with The recoil energy of the remaining 4 He nucleus is 3.
This is many times more than what was needed to overcome the energy barrier. If the reactants have a distribution of velocities, e. At these temperatures, well above typical ionization energies This is an extremely challenging barrier to overcome on Earth, which explains why fusion research has taken many years to reach the current advanced technical state. If matter is sufficiently heated hence being plasma and confined, fusion reactions may occur due to collisions with extreme thermal kinetic energies of the particles.
Thermonuclear weapons produce what amounts to an uncontrolled release of fusion energy. Controlled thermonuclear fusion concepts use magnetic fields to confine the plasma. Inertial confinement fusion ICF is a method aimed at releasing fusion energy by heating and compressing a fuel target, typically a pellet containing deuterium and tritium.
Inertial electrostatic confinement is a set of devices that use an electric field to heat ions to fusion conditions. The most well known is the fusor. Starting in , a number of amateurs have been able to do amateur fusion using these homemade devices. If the energy to initiate the reaction comes from accelerating one of the nuclei, the process is called beam-target fusion; if both nuclei are accelerated, it is beam-beam fusion. Accelerator-based light-ion fusion is a technique using particle accelerators to achieve particle kinetic energies sufficient to induce light-ion fusion reactions.
Accelerating light ions is relatively easy, and can be done in an efficient manner—requiring only a vacuum tube, a pair of electrodes, and a high-voltage transformer; fusion can be observed with as little as 10 kV between the electrodes.
Fission and Fusion
The energy harnessed in nuclei is released in nuclear reactions. Fission is the splitting of a heavy nucleus into lighter nuclei and fusion is the combining of nuclei to form a bigger and heavier nucleus. The consequence of fission or fusion is the absorption or release of energy. Protons and neutrons make up a nucleus, which is the foundation of nuclear science. Fission and fusion involves the dispersal and combination of elemental nucleus and isotopes, and part of nuclear science is to understand the process behind this phenomenon. Adding up the individual masses of each of these subatomic particles of any given element will always give you a greater mass than the mass of the nucleus as a whole.
It seems that you're in Germany. We have a dedicated site for Germany. Authors: Krappe , Hans J. This book brings together various aspects of the nuclear fission phenomenon discovered by Hahn, Strassmann and Meitner almost 70 years ago. Beginning with an historical introduction the authors present various models to describe the fission process of hot nuclei as well as the spontaneous fission of cold nuclei and their isomers.
Fission occurs when a neutron slams into a larger atom, forcing it to excite and spilt into two smaller atoms—also known as fission products. Additional neutrons are also released that can initiate a chain reaction. Uranium and plutonium are most commonly used for fission reactions in nuclear power reactors because they are easy to initiate and control. The energy released by fission in these reactors heats water into steam. The steam is used to spin a turbine to produce carbon-free electricity. Fusion occurs when two atoms slam together to form a heavier atom, like when two hydrogen atoms fuse to form one helium atom. This is the same process that powers the sun and creates huge amounts of energy—several times greater than fission.
If these neutrons are absorbed by other nuclei, this causes a chain reaction. • For the chain reaction to occur, there has to be a critical mass. o For uranium, this is.
Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. The nuclear fusion program of the United States should seek to develop this technology sufficiently for comparison with fast breeder reactors, solar power, and other long-term sources of energy. The technology must still be tested for engineering achievability, environmental characteristics, and reasonable cost.
Nuclear fusion and nuclear fission are different types of reactions that release energy due to the presence of high-powered atomic bonds between particles found within a nucleus. In fission, an atom is split into two or more smaller, lighter atoms. Fusion, in contrast, occurs when two or more smaller atoms fuse together, creating a larger, heavier atom. Nuclear fusion is the reaction in which two or more nuclei combine, forming a new element with a higher atomic number more protons in the nucleus.
Uranium U is one of the isotopes that fissions easily. The process may be controlled nuclear power or uncontrolled nuclear weapons.
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A nuclear reactor , formerly known as an atomic pile , is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nuclear fission is passed to a working fluid water or gas , which in turn runs through steam turbines. These either drive a ship's propellers or turn electrical generators ' shafts. Nuclear generated steam in principle can be used for industrial process heat or for district heating.
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A nuclear reaction takes place when a nucleus is struck by another nucleus or particle. Compare with chemical reactions! If the original nucleus is transformed.