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    what particle collides with a fissionable nucleus in order to begin the fission process?

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    Nuclear Fission

    Nuclear Fission

    Nuclear Fission Nuclear Fission

    Nuclear fission occurs when an atom splits into two or more smaller atoms, most often the as the result of neutron bombardment.

    LEARNING OBJECTIVES

    Describe the process of nuclear fission

    KEY TAKEAWAYS

    Key Points

    Nuclear fission is a process where the nucleus of an atom is split into two or more smaller nuclei, known as fission products.

    The fission of heavy elements is an exothermic reaction, and huge amounts of energy are released in the process.

    Nuclear fission occurs with heavier elements, where the electromagnetic force pushing the nucleus apart dominates the strong nuclear force holding it together.

    In order to initiate most fission reactions, an atom is bombarded by a neutron to produce an unstable isotope, which undergoes fission.

    When neutrons are released during the fission process, they can initiate a chain reaction of continuous fission which sustains itself.

    Key Terms

    fissile: Capable of undergoing nuclear fission.nucleon: One of the subatomic particles of the atomic nucleus, i.e. a proton or a neutron.nuclear fission: Radioactive decay process in which the nucleus of an atom splits into lighter nuclei.

    Nuclear fission is a process by which the nucleus of an atom is split into two or more smaller nuclei, known as fission products. The fission of heavy elements is an exothermic reaction, and huge amounts of energy are released in the process. The nuclei produced are most often of comparable but slightly different sizes, typically with a mass ratio of products of about 3:2 for common fissile isotopes. Most fissions are binary fissions that produce two charged fragments. Occasionally, about 2 to 4 times per 1000 events, three positively charged fragments are produced, which indicates a ternary fission. The smallest of these fragments in ternary processes ranges from the size of a proton to the size of an argon nucleus.

    Nuclear fission: In nuclear fission, an unstable atom splits into two or more smaller pieces that are more stable, and releases energy in the process. The fission process also releases extra neutrons, which can then split additional atoms, resulting in a chain reaction that releases a lot of energy. There are also ways to modulate the chain reaction by soaking up the neutrons.Nuclear fission of U-235: If U-235 is bombarded with a neutron (light blue small circe), the resulting U-236 produced is unstable and undergoes fission. The resulting elements (shown here as Kr-92 and Ba-141) do not contain as many nucleons as U-236, with the remaining three neutrons being released as high-energy particles, able to bombard another U-235 atom and maintain a chain reaction.

    Origin of Nuclear Instability

    Within the nucleus, there are different forces that act between the particles. The strong nuclear force is the force between two or more nucleons. This force binds protons and neutrons together inside the nucleus, and it is most powerful when the nucleus is small and the nucleons are close together. The electromagnetic force causes the repulsion between like-charged protons. These two forces produce opposite effects in the nucleus. The strong nuclear force acts to hold all the protons and neutrons close together, while the electromagnetic force acts to push protons further apart.

    In atoms with small nuclei, the strong nuclear force overpowers the electromagnetic force. As the nucleus gets bigger, the electromagnetic force becomes greater than the strong nuclear force. In these nuclei, it’s possible for particles and energy to be ejected from the nucleus. These nuclei are called unstable, and this instability can result in radiation and fission.

    Neutron Bombardment

    In order to initiate fission, a high-energy neutron is directed towards a nucleus, such as 235U. The combination of these two produces 236U, which is an unstable element that undergoes fission. The resulting fission process often releases additional neutrons, which can go on to initiate other 235U atoms, forming a chain reaction. While nuclear fission can occur without this neutron bombardment, in what would be termed spontaneous fission, this is a rare occurrence; most fission reactions, especially those utilized for energy and weaponry, occur via neutron bombardment. If an element can be induced to undergo fission via neutron bombardment, it is said to be fissile.

    The Atomic Bomb

    Atomic bombs are nuclear weapons that use the energetic output of nuclear fission to produce massive explosions.

    LEARNING OBJECTIVES

    Describe the chemical reaction which fuels an atomic bomb

    KEY TAKEAWAYS

    Key Points

    Atomic bombs are nuclear weapons that use the energetic output of nuclear fission to produce massive explosions.

    Only two nuclear weapons have been used in the course of warfare, both by the U.S. near the end of World War II.

    In fission weapons, a mass of fissile material is assembled into a supercritical mass either by shooting one piece of sub-critical material into another (the “gun” method) or by compressing a sub-critical sphere of material using chemical explosives (the “implosion” method).

    Key Terms

    nuclear weapon: A weapon that derives its energy from the nuclear reactions of either fission or fusion.fusion: A nuclear reaction in which nuclei combine to form more massive nuclei with the concomitant release of energy and often neutrons.

    Source : courses.lumenlearning.com

    Nuclear fission

    Nuclear fission

    From Wikipedia, the free encyclopedia

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    Induced fission reaction. A neutron is absorbed by a uranium-235 nucleus, turning it briefly into an excited uranium-236 nucleus, with the excitation energy provided by the kinetic energy of the neutron plus the forces that bind the neutron. The uranium-236, in turn, splits into fast-moving lighter elements (fission products) and releases several free neutrons, one or more "prompt gamma rays" (not shown) and a (proportionally) large amount of energy.

    Nuclear physics

    Nucleus · Nucleons (p, n) · Nuclear matter · Nuclear force · Nuclear structure · Nuclear reaction

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    Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei. The fission process often produces gamma photons, and releases a very large amount of energy even by the energetic standards of radioactive decay.

    Nuclear fission of heavy elements was discovered on Monday 19 December 1938, by German chemist Otto Hahn and his assistant Fritz Strassmann in cooperation with Austrian-Swedish physicist Lise Meitner. Hahn understood that a "burst" of the atomic nuclei had occurred.[1][2] Meitner explained it theoretically in January 1939 along with her nephew Otto Robert Frisch. Frisch named the process by analogy with biological fission of living cells. For heavy nuclides, it is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments (heating the bulk material where fission takes place). Like nuclear fusion, for fission to produce energy, the total binding energy of the resulting elements must be greater than that of the starting element.

    Fission is a form of nuclear transmutation because the resulting fragments (or daughter atoms) are not the same element as the original parent atom. The two (or more) nuclei produced are most often of comparable but slightly different sizes, typically with a mass ratio of products of about 3 to 2, for common fissile isotopes.[3][4] Most fissions are binary fissions (producing two charged fragments), but occasionally (2 to 4 times per 1000 events), positively charged fragments are produced, in a ternary fission. The smallest of these fragments in ternary processes ranges in size from a proton to an argon nucleus.

    Apart from fission induced by a neutron, harnessed and exploited by humans, a natural form of spontaneous radioactive decay (not requiring a neutron) is also referred to as fission, and occurs especially in very high-mass-number isotopes. Spontaneous fission was discovered in 1940 by Flyorov, Petrzhak, and Kurchatov[5] in Moscow, in an experiment intended to confirm that, without bombardment by neutrons, the fission rate of uranium was negligible, as predicted by Niels Bohr; it was not negligible.[5]

    The unpredictable composition of the products (which vary in a broad probabilistic and somewhat chaotic manner) distinguishes fission from purely quantum tunneling processes such as proton emission, alpha decay, and cluster decay, which give the same products each time. Nuclear fission produces energy for nuclear power and drives the explosion of nuclear weapons. Both uses are possible because certain substances called nuclear fuels undergo fission when struck by fission neutrons, and in turn emit neutrons when they break apart. This makes a self-sustaining nuclear chain reaction possible, releasing energy at a controlled rate in a nuclear reactor or at a very rapid, uncontrolled rate in a nuclear weapon. In their second publication on nuclear fission in February of 1939, Hahn and Strassmann predicted the existence and liberation of additional neutrons during the fission process, opening up the possibility of a nuclear chain reaction.

    The amount of free energy contained in nuclear fuel is millions of times the amount of free energy contained in a similar mass of chemical fuel such as gasoline, making nuclear fission a very dense source of energy. The products of nuclear fission, however, are on average far more radioactive than the heavy elements which are normally fissioned as fuel, and remain so for significant amounts of time, giving rise to a nuclear waste problem. Concerns over nuclear waste accumulation and the destructive potential of nuclear weapons are a counterbalance to the peaceful desire to use fission as an energy source.

    Contents

    1 Physical overview 1.1 Mechanism

    1.1.1 Radioactive decay

    1.1.2 Nuclear reaction

    1.2 Energetics 1.2.1 Input 1.2.2 Output

    1.3 Product nuclei and binding energy

    1.4 Origin of the active energy and the curve of binding energy

    1.5 Chain reactions

    1.6 Fission reactors

    1.7 Fission bombs 2 History

    2.1 Discovery of nuclear fission

    2.2 Fission chain reaction realized

    2.3 Manhattan Project and beyond

    2.4 Natural fission chain-reactors on Earth

    Source : en.wikipedia.org

    Fission and Fusion

    CK-12 Chemistry - Basic is a NEW high school FlexBook® textbook covering Scientific Method, Matter, Atomic Structure, Elements, Chemical Reactions, Stoichiometry, Chemical Kinetics, Physical States of Matter, Thermodynamics, Nuclear & Organic Chemistry.

    24.3 Fission and Fusion

    Difficulty Level: Basic | Created by: CK-12

    Last Modified: Oct 02, 2015

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