Concepts of Nuclear Fission and Nuclear Fusion

7/29/2019 Concepts of Nuclear Fission and Nuclear Fusion

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A B S T R A C T

Nuclear fission is induced by bombarding sub atomic particles with the atomic nucleus of

radioactive substance; this process induces a chain reaction wherein neutrons are released along

with humungous heat energy; the neutrons emitted which increases exponentially until the

substance is decayed completely. Further these neutrons can trigger yet more fission events.

Energy released in fission is in form of kinetic energy of fission fragments and Electromagnetic

radiations (gamma rays); in nuclear reactor this energy is converted to heat by collision of

particles and gamma rays with reactor walls and working fluid. Typical fission event releases

about 200MeV of energy (eV is kinetic energy gained by an unbound electron when acceleratedto a potential difference of 1 volt)

Nuclear fusion is the process of joining of 2 atomic nucleuses to form a single heavy nucleus; it

involves absorption of large quantities of energy. The ratio of atomic mass to mass number is

lower the heavier the nucleus is this is known as mass defect. So fusion of lighter nuclei into

heavier nuclei leads to loss of mass but not nucleons this loss of mass is released as energy in

accordance with E=mc2; the difference in mass which we find is the binding energy; for a

molecule to be broken to its atoms we require such an energy that accounts for the difference in

mass which we earlier called it as mass defect.

InAtom bomb, the Explosive energy is got by fission reaction alone. This is triggered by 2 types

Gun-type wherein subatomic particles are shot to fissile material (supercritical mass); other one

is by compressing fissile material core so that due to instability the reaction is triggered.

In Hydrogen bomb, the Explosive energy is got by fusion process alone. This is triggered by

using fission reaction to compress and heat the fusion fuel. This bomb consists of 2 sections, 1 is

fission section wherein reaction triggers to give enough energy for the fusion process to take

place and the other one is fusion section wherein fusion fuel is concentrated.


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NUCLEAR FISSION

PHYSICAL OVERVIEW:

Mechanics:

Nuclear fission can occur without neutronbombardment, as a type ofradioactive decay. This

type of fission (called spontaneous fission) is rare except in a few heavy isotopes. In engineered

nuclear devices, essentially all nuclear fission occurs as a "nuclear reaction"a bombardment-

driven process that results from the collision of two subatomic particles. In nuclear reactions, a

subatomic particle collides with an atomic nucleus and causes changes to it. Nuclear reactions

are thus driven by the mechanics of bombardment, not by the relatively constant exponential

decay and half-life characteristic of spontaneous radioactive processes.

Many types ofnuclear reactions are currently known. Nuclear fission differs importantly from

other types of nuclear reactions, in that it can be amplified and sometimes controlled via a

nuclearchain reaction. In such a reaction, free neutrons released by each fission event can trigger

yet more events, which in turn release more neutrons and cause more fission.

The chemical element isotopes that can sustain a fission chain reaction are called nuclear fuels,

and are said to befissile. The most common nuclear fuels are235

U (the isotope ofuranium with

an atomic mass of 235 and of use in nuclear reactors) and239

Pu (the isotope ofplutonium with

an atomic mass of 239). These fuels break apart into a bimodal range of chemical elements with

atomic masses centering near 95 and 135 u(fission products). Most nuclear fuels

undergo spontaneous fission only very slowly, decaying instead mainly via an alpha/beta decay

chain over periods ofmillennia to eons. In a nuclear reactoror nuclear weapon, the

overwhelming majority of fission events are induced by bombardment with another particle, a

neutron, which is itself produced by prior fission events.

Nuclear fission is normally the result of the nuclear excitation energy produced when a

fissionable nucleus captures a neutron. This energy, resulting from the neutron capture, is a result

of breaking of the attractive nuclear force acting between the neutron and nucleus. It is enough to

deform the nucleus into a double-lobed "drop," to the point that nuclear fragments exceed the

distances at which the nuclear force can hold two groups of charged nucleons together, and when

this happens, the two fragments complete their separation and then are driven further apart by

their mutually repulsive charges, in a process which becomes irreversible with greater and

greater distance.
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Concepts of nuclear fission and nuclear fusion

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The liquid drop model of the atomic nucleuspredicts equal-sized fission products as a

mechanical outcome of nuclear deformation. The more sophisticated nuclear shell model is

needed to mechanistically explain the route to the more energetically-favorable outcome, in

which one fission product is slightly smaller than the other.

ENERGETICS:

Input:

The fission of a heavy nucleus requires a total input energy of about 7 to 8 MeV to initiallyovercome the strong force which holds the nucleus into a spherical or nearly spherical shape, and

from there, deform it into a two-lobed ("peanut") shape in which the lobes are able to continue to

separate from each other, pushed by their mutual positive charge, in the most common process of

binary fission (two positively-charged fission products + neutrons). Once the nuclear lobes have

been pushed to a critical distance, beyond which the short range strong force can no longer hold

them together, the process of their separation proceeds from the energy of the (longer

range) electromagnetic repulsion between the fragments. The result is two fission fragments

moving away from each other, at high energy.

About 6 MeV of the fission-input energy is supplied by the simple binding of the neutron to the

nucleus via the strong force, however in many fissionable isotopes this amount of energy is notenough for fission. If no additional energy is supplied by any other mechanism, the nucleus will

not fission, but will merely absorb the neutron, as happens when U-238 absorbs slow neutrons to

become U-239. The remaining energy to initiate fission can be supplied by two other

mechanisms: one of these is the kinetic energy of the incoming neutron, which is increasingly

able to fission a fissionable heavy nucleus as it exceeds a kinetic energy of one MeV or more

(so-called fast neutrons). Such high energy neutrons are able to fission U-238 directly. However,
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this process cannot happen to a great extent in a nuclear reactor, as too small a fraction of the

fission neutrons produced by any type of fission have enough energy to directly fission U-238.

Output:

Typical fission events release about two hundred million eV (200 MeV; eV is kinetic energy

gained by an unbound electron when accelerated to a potential difference of 1 volt) of energy for

each fission event. By contrast, most chemical oxidation reactions (such as burning coal orTNT)

release at most a few eVper event, so nuclear fuel contains at least ten million times more usable

energy per unit mass than does chemical fuel. The energy of nuclear fission is released as kinetic

energy of the fission products and fragments, and as electromagnetic radiation in the form

ofgamma rays; in a nuclear reactor, the energy is converted to heat as the particles and gamma

rays collide with the atoms that make up the reactor and its working fluid, usually water.

When a uranium nucleus fissions into two daughter nuclei fragments, energy of ~200 MeV is

released. For uranium-235, typically ~169 MeV appears as the kinetic energy of the daughter

nuclei, which fly apart at about 3% of the speed of light, due to Coulomb repulsion. Also, an

average of 2.5 neutrons is emitted with a kinetic energy of ~2 MeV each. The fission reaction

also releases ~7 MeV in prompt gamma ray photons. The total prompted fission energy amounts

to about 181 MeV or ~ 89% of the total energy which is eventually released by fission over time.

The remaining ~ 11% is released in beta decays which have various half-lives.

A kilogram ofuranium-235 (U-235) converted via nuclear processes releases approximately

three million times more energy than a kilogram of coal burned conventionally

(7.2 1013

joulesper kilogram of uranium-235 versus 2.4 107

joules per kilogram of coal).

Product nuclei and binding energy:

In nuclear fission events the nuclei may break into any combination of lighter nuclei, but the

most common event is not fission to equal mass nuclei of about mass 120; the most common

event (depending on isotope and process) is a slightly unequal fission in which one daughter

nucleus has a mass of about 90 to 100 u and the other the remaining 130 to 140 u. Unequal

fissions are energetically more favorable because this allows one product to be closer to the

energetic minimum near mass 60 u (quarter of average fissionable mass), while the other nucleus

with mass 135 u is still not far out of the range of the most tightly bound nuclei.

Chain Reaction:
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5

Several heavy elements, such as uranium, thorium, and plutonium, undergo both spontaneous

fission, a form ofradioactive decay and induced fission, a form ofnuclear reaction. Elemental

isotopes that undergo induced fission when struck by a free neutron are called fissionable;

isotopes that undergo fission when struck by a thermal, slow moving neutron are alsocalled fissile.All fissionable and fissile isotopes undergo a small amount of spontaneous fissionwhich releases a few free neutrons. These neutrons which escape has a mean lifetime of about 15

minutes before decaying to protons and beta particles. However, neutrons almost invariably

impact and are absorbed by other nuclei in the vicinity long before this happens. If enough

nuclear fuel is assembled in one place, or if the escaping neutrons are sufficiently contained, then

these freshly emitted neutrons outnumber the neutrons that escape from the assembly, and

a sustained nuclear chain reaction will take place.

Nuclear Reactor:

Critical fission reactors are the most common type of nuclear reactor, in critical reactors neutrons

produced are used to induce further fission events. Reactors that produce engineered but not self-

sustaining fission reactions are known as sub critical fission reactors. Critical fission reactors are

intended for 3 primary purposes, they are
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Power reactorsare intended to produce heat for nuclear power, either as part of

a generating station or a local power system such as a nuclear submarine.

Research reactorsare intended to produce neutrons and/or activate radioactive sources for

scientific, medical, engineering, or other research purposes.

Breeder reactorsare intended to produce nuclear fuels in bulk from more abundant isotopes.

The better known fast breeder reactormakes239

Pu (a nuclear fuel) from the naturally very

abundant238

U (not a nuclear fuel).

Radioactivity control in a reactor:

The power output of the reactor is adjusted by controlling how many neutrons are able to create

more fission. Control rods are the neutron absorbers that help in absorbing neutrons released in

the process and ensuring lesser number of neutrons is available for further fission process; so

pushing the control rods deeper into the reactor will reduce its power output, and extracting the

rods will increase it.

In some reactors, the coolant also acts as a neutron moderator. A moderator increases the power

of the reactor by causing the fast neutrons that are released from fission to lose energy and

become thermal neutrons. Thermal neutrons are more likely than fast neutrons to cause fission,

so more neutron moderation means more power output from the reactors. If the coolant is a

moderator, then temperature changes can affect the density of the coolant/moderator and

therefore change power output. A higher temperature coolant would be less dense, and therefore

a less effective moderator.

In other reactors the coolant acts as a poison by absorbing neutrons in the same way that the

control rods do. In these reactors power output can be increased by heating the coolant, which

makes it a less dense poison. Nuclear reactors generally have automatic and manual systems

to scram the reactor in an emergency shutdown. These systems insert large amounts of poison

(often boron in the form of boric acid) into the reactor to shut the fission reaction down if unsafe

conditions are detected or anticipated.

The normal fission process also produces iodine-135, which in turn decays with a half-life of

under seven hours to new xenon-135 (xenon-135 is a good neutron absorber). Thus, if the reactor

is shut down, iodine-135 in the reactor continues to decay to xenon-135 to the point that makes

re-starting the reactor more difficult, for a day or two, than when first shut down (this temporary

state is the "iodine pit."), the extra xenon-135 is "burned off" by transmuting it to xenon-136 (not

a neutron poison), within a few hours the reactor may become unstable as a result of such a
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"xenon burn off (power) transient," and then rapidly become overheated, unless control rods are

reinserted in order to replace the neutron absorption of the lost xenon-135. Failure to properly

follow such a procedure was a key step in the Chernobyl disaster.

Components of a nuclear reactor:

Nuclear fuelis the material that can be consumed by fission or fusion to harness nuclear energy.

The most common fissile nuclear fuels are Uranium 235 (235U) and Plutonium

239 (239

Pu). Plutonium-238 and some other elements are used to produce small amounts ofnuclear power by radioactive decay in radioisotope thermoelectric generators and other atomic

batteries. Light nuclides such as3H (tritium) are used as fuel for nuclear fusion.

Nuclear reactor core of a typical pressurized water reactororboiling water reactorare pencil-

thin nuclear fuel rods, each about 12 feet (3.7 m) long, which are grouped by the hundreds in

bundles called "fuel assemblies". Inside each fuel rod, pellets of uranium, or more commonly
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uranium oxide, are stacked end to end. Also inside the core are control rods, filled with pellets of

substances like boron orhafnium orcadmium that readily capture neutrons,this is a typical water

moderated reactor. There are also graphite moderated reactors in use which uses solid graphite

for neutron moderator and water as coolant; this was the type of reactor involved in Chernobyl

disaster.

Neutron moderator is a medium that reduces the speed offast neutrons, thereby turning them

into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235.

Commonly used moderators are, light water (75% of Worlds rectors), solid graphite (20%) and

heavy water (5%). The first couple of collisions with the moderator may be of sufficiently high

energy to excite the nucleus of the moderator. Such a collision is inelastic. As the energy of the

neutron is lowered, the collisions become predominantly elastic, i.e., the total kinetic energy and

momentum of the system is conserved. It is not impossible for fast neutrons to cause fission, just

much less likely. The newly-released fast neutrons, moving at roughly 10% of the speed of light,must be slowed down or "moderated," typically to speeds of a few kilometers per second, if they

are to be likely to cause further fission in neighboring235

U nuclei and hence continue the chain

reaction.

Neutron poison is a substance with a large neutron absorption cross-section in applications, such

as nuclear reactors. Some of these poisons deplete as they absorb neutrons during reactor

operation, while others remain relatively constant. Some of the fission products may also act as

nuclear poison (xenon-135); with such products the chain reactions may come to standstill, this

may lead to decrease in efficiency and cause instability in the reactor.

During operation of a reactor the amount of fuel contained in the core decreases monotonically.

If the reactor is to operate for a long period of time, fuel in excess of that needed for

exact criticality must be added when the reactor is fueled. The positive reactivity due to the

excess fuel must be balanced with negative reactivity from neutron-absorbing material (control

rods).

Coolant is a fluid which flows through a device to prevent its overheating, transferring the heat

produced by the device to other devices that use or dissipate it. An ideal coolant has high thermal

capacity, low viscosity, is low-cost, non-toxic, and chemically inert, neither causing nor

promoting corrosion of the cooling system. Coolant can either keep its phase or can undergo a

phase change.

Gases: Air is the common form of coolant in this phase. Hydrogen is used as a high-

performance gaseous coolant. Its thermal conductivity is higher than of all gases, it has
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high specific heat capacity, and low density and therefore low viscosity, which is an

advantage for rotary machines susceptible to wind age losses. Inert gases are frequently

used as coolants in gas-cooled nuclear reactors. Helium is the most favored coolant due

to its low tendency to absorb neutrons and become radioactive.

Liquids: The most common coolant is water. Its high heat capacity and low cost makes it

a suitable heat-transfer medium. It is usually used with additives, like corrosion

inhibitors and antifreeze. Sodium or sodium-potassium alloy are frequently used; in

special cases lithium can be employed. Another liquid metal used as a coolant is lead, in

e.g. lead cooled fast reactors, or a lead-bismuth alloy. Some early fast neutron

reactors used mercury. There are coolants in liquid gases, Nano fluids, and solids which

are extensively used for various other purposes.

Control rod is a rod made ofchemical elements capable of absorbing many neutrons withoutundergoing fission by themselves. Control rods are usually combined into control rod assemblies

typically 20 rods for a commercial Pressurized Water Reactor (PWR) assembly and

inserted into guide tubes within a fuel element. The number of control rods inserted and the

distance by which they are inserted can be varied to control the reactivity of the reactor.

Silver-indium-cadmium alloys, generally 80% Ag, 15% in, and 5% Cd, are common control

rod material forpressurized water reactors. It has to be encased in stainless steel to prevent

corrosion in hot water.

Boron is another common neutron absorber. The wide absorption spectrum makes it suitable as a

neutron shield. Boron carbide is used as a control rod material in both pressurized water

reactors and boiling water reactors.

Hafnium, Dysprosium titanate, Hafnium diboride are some of the control rod material which

are also used.

Steam turbineis a mechanical device that extracts thermal energy from pressurized steam, andconverts it into rotary motion. To maximize turbine efficiency the steam is expanded, generating

work, in a number of stages. These stages are characterized by how the energy is extracted from

them and are known as either impulse or reaction turbines.

Impulse turbine has fixed nozzles that orient the steam flow into high speed jets which is

directed to bucket shaped blades mounted along the circumference of the rotor.

In Reaction turbine, the rotor blades themselves are arranged to form convergent nozzles.

Steam is directed onto rotor by the fixed vanes of stator; the nozzle effect (increase in velocity) is

got by the set of fixed vanes. The steam then changes direction and increases its speed relative to

the speed of the blades.
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NUCLEAR FUSION

INTRODUCTION:

Nuclear fusion is the process by which two or more atomic nucleijoin together, or "fuse", toform a single heavier nucleus.This is usually accompanied by the release or absorption of large

quantities ofenergy. Large-scale thermonuclear fusion processes, involving many nuclei fusing

at once, must occur in matter at very high densities and temperatures. The fusion of two nuclei

with lower masses than iron generally release energy while the fusion of nuclei heavier than iron

absorb energy.

Nuclear fusion occurs naturally in all active stars. Synthetic fusion as a result of human actions

has also been achieved, although this has not yet been completely controlled as a source

ofnuclear power. In the laboratory, successful nuclear physics experiments have been carried outthat involves the fusion of many different varieties of nuclei, but the energy output has been

negligible in these studies. In fact, the amount of energy put into the process has always

exceeded the energy output. Uncontrolled nuclear fusion which is been carried out as resulted in

deliberate explosion. These explosions have always used the heavy isotopes ofhydrogen,

deuterium (H-2) and tritium (H-3), and never the much more common isotope of hydrogen (H-

1), sometimes called "protium".

Overview:

Fusion ofdeuterium with tritium creatinghelium-4, freeing a neutron, and releasing 17.59 MeVof energy
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Generally, when dealing with elements lighter than iron, the lower the ratio ofatomic mass (total

mass of protons and neutrons) to mass number (total number of protons and neutrons) is the

heavier the nucleus is. This is known as mass defect. So fusion of lighter nuclei into heavier

nuclei leads to loss of mass even though no nucleons are lost. This lost mass is released asenergy in accordance withE=mc

2.

Research into controlled fusion, with the aim of producing fusion power for the production of

electricity, has been conducted for over 50 years. It has been accompanied by extreme scientific

and technological difficulties, but has resulted in progress.

It takes considerable energy to force nuclei to fuse, even those of the lightest element, hydrogen.

This is because all nuclei have a positive charge (due to their protons), and as like charges repel,

nuclei strongly resist being put too close together. Accelerated to high speeds (that is, heated tothermonuclear temperatures), they can overcome this electrostatic repulsion and get close enough

for the attractive nuclear force to be sufficiently strong to achieve fusion. 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 during fusion process is large compared to

chemical reaction, because the binding energy that holds the nucleus together is large compared

to energy that holds electrons to the nucleus.

The hierarchy of energy levels given out in different processes is,

Nuclear fission


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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

forcebetween theirpositively chargedprotons. If two nuclei can be brought close enough

together, however, the electrostatic repulsion can be overcome by the attractive nuclear force,

which is stronger at close distances. The electrostatic force, on the other hand, is an inverse-

square force (the electrostatic force between the 2 nuclei is inversely proportional to the square

of the distance between them), 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 get larger.

The net result of these opposing 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. 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 in contact can the

strong nuclear force take over. 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.

Using deuterium-tritium fuel, the resulting energy barrier is about 0.01 MeV. The (intermediate)

result of the fusion is an unstable5He nucleus, which immediately ejects a neutron with

14.1 MeV. The recoil energy of the remaining4He nucleus is 3.5 MeV, so the total energy

liberated is 17.6 MeV. This is many times more than what was needed to overcome the energy

barrier.

If the energy to initiate the reaction comes from accelerating one of the nuclei, the process is

called beam-targetfusion; if both nuclei are accelerated, it is beam-beam fusion. If the nuclei are

part ofplasma near thermal equilibrium, the process is called thermonuclearfusion.

The other effect is quantum tunneling (quantum mechanicalphenomenon where a particle

tunnels through a barrierthat it classically could not surmount because its total kinetic energy is

lower than the potential energy). The nuclei do not actually have to have enough energy to

overcome the Coulomb barrier completely. If they have nearly enough energy, they can tunnel

through the remaining barrier. For this reason fuel at lower temperatures will still undergo fusion

events, at a lower rate.

Possibilities of confinement:

Gravitational confinement: One force capable of confining the fuel well enough is gravity. The

mass needed, however, is so great that gravitational confinement is only found in starsthe least

massive stars capable of sustained fusion are red dwarfs, while brown dwarfs are able to

fuse deuterium and lithium if they are of sufficient mass.

Magnetic confinement: Electrically charged particles (such as fuel ions) will follow magnetic

field lines. The fusion fuel can therefore be trapped using a strong magnetic field.
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Inertial confinement: A third confinement principle is to apply a rapid pulse of energy to a large

part of the surface of a pellet of fusion fuel, causing it to simultaneously "implode" and heat to

very high pressure and temperature. If the fuel is dense enough and hot enough, the fusion

reaction rate will be high enough to burn a significant fraction of the fuel before it has dissipated.

To achieve these extreme conditions, the initially cold fuel must be explosively compressed.

Inertial confinement is used in the hydrogen bomb, where the driver is X-rays created by a

fission bomb. Inertial confinement is also attempted in controlled nuclear fusion, where the

driver is a laser, ion, orelectronbeam, or a Z-pinch.

Production methods:

Muon-catalyzed fusion: Muon-catalyzed fusion is a well-established and reproducible fusion

process that occurs at ordinary temperatures. It was studied in detail by Steven Jones in the early

1980s. It has not been reported to produce net energy. Net energy production from this reactioncannot occur because of the energy required to create muons, their 2.2 s half-life, and the

chance that a muon will bind to the new alpha particle and thus stop catalyzing fusion.

Hot fusion: In hot fusion, the fuel reaches tremendous temperature and pressure inside a fusion

reactorornuclear weapon (or star).The methods in the second group are examples of non-

equilibrium systems, in which very high temperatures and pressures are produced in a relatively

small region adjacent to material of much lower temperature. Todd Rider demonstrated that all

such systems will leak energy at a rapid rate due to bremsstrahlungproduced when electrons in

the plasma hit other electrons orions at a cooler temperature and suddenly decelerate.

Astrophysical chain reactions:

The most important fusion process in nature is the one that powers stars. The net result is the

fusion of fourprotons into one alpha particle, with the release of two positrons,

two neutrinos (which changes two of the protons into neutrons), and energy, but several

individual reactions are involved, depending on the mass of the star. For stars the size of the sun

or smaller, the proton-proton chain dominates. In heavier stars, the CNO cycle is more important.

Both types of processes are responsible for the creation of new elements as part of stellar

nucleosynthesis.
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The proton-proton chain dominates in stars the size of the Sun or smaller.

NUCLEAR WEAPON

Introduction:

The first nuclear weapons were gravity bombs, such as this "Fat Man"weapon dropped on Nagasaki, Japan.
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A nuclear weapon is an explosive device that derives its destructive force from nuclear

reactions, eitherfission or a combination of fission and fusion. The first fission (atomic) bomb

test released the same amount of energy as approximately 20,000 tons of TNT. The first

thermonuclear (hydrogen) bomb test released the same amount of energy as approximately10,000,000 tons of TNT.

Types of nuclear weapons:

Atomic bombs: The explosive energy is got through the nuclear fission reactions alone. Such

fission weapons are commonly referred to as atomic bombs or A-bombs.

The two basic fission weapon designs

In fission weapons, a mass offissile material (enriched uranium orplutonium) is assembled into

a supercritical massthe amount of material needed to start an exponentially growing nuclear

chain reactioneither 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 to many

times its original density (the implosion method). The latter approach is considered more

sophisticated than the former and only the latter approach can be used if the fissile material is

plutonium.
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A major challenge in all nuclear weapon designs is to ensure that a significant fraction of the fuel

is consumed before the weapon destroys itself. The amount of energy released by fission bombs

can range from the equivalent of less than a ton ofTNT upwards of 500,000 tons (500 kilotons)

of TNT.

Hydrogen bombs: The explosive energy is got through the nuclear fusion reaction alone. Suchfusion weapons are generally referred to as thermonuclear weapons or more colloquially

as H- bombs, as they rely on fusion reactions between isotopes of

hydrogen (deuterium and tritium). However, all such weapons derive a significant portion, and

sometimes a majority, of their energy from fission (including fission induced by neutrons).

Unlike fission weapons, there are no inherent limits on the energy released by thermonuclear

weapons. Only six countriesUnited States, Russia, United Kingdom, People's Republic of

China, France and Indiahave conducted thermonuclear weapon tests.

Working principle:

The basics of the TellerUlam designfor a hydrogen bomb: a fission bomb uses radiation to compress and heat a

separate section of fusion fuel.

Thermonuclear bombs work by using the energy of a fission bomb to compress and heat fusion

fuel. In the Teller-Ulam design, which accounts for all multi-megaton yield hydrogen bombs,

this is accomplished by placing a fission bomb and fusion fuel (tritium, deuterium, or lithium

deuteride) in proximity within a special, radiation-reflecting container. When the fission bomb is

detonated, gamma and X-rays emitted first compress the fusion fuel, then heat it to

thermonuclear temperatures. The ensuing fusion reaction creates enormous numbers of high-
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speed neutrons, which can then induce fission in materials not normally prone to it, such

as depleted uranium. Each of these components is known as a "stage", with the fission bomb as

the "primary" and the fusion capsule as the "secondary". In large hydrogen bombs, about half of

the yield, and much of the resulting nuclear fallout, comes from the final fission of depleted

uranium.
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REFERENCES

en.wikipedia.org.

The Nuclear Physics and Reactor theory Handbook.

electricalandelectronics.org

tutorvista.com

Documents

Concepts of Nuclear Fission and Nuclear Fusion