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A neutron reflector is any material that reflects neutron
Neutron

The neutron is a subatomic particle with no net electric charge and a mass slightly larger than that of a proton.Neutrons are usually found in atomic nucleus....
s. Usually, this term refers to the elastic scattering rather than to a specular reflection
Specular reflection

Specular reflection is the perfect, mirror-like reflection of light from a surface, in which light from a single incoming direction is reflected into a single outgoing direction....
. This reflector (scatterer) may be graphite
Graphite

The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Greek language ??afe?? : "to draw/write", for its use in pencils, where it is commonly called lead, as distinguished from the actual metallic element lead....
, beryllium
Beryllium

Beryllium is a chemical element with the symbol Be and atomic number 4.A Bivalent element, beryllium is found naturally only combined with other elements in minerals....
, or other materials. A neutron reflector can make an otherwise subcritical mass of fissile material critical, or increase the amount of nuclear fission that a critical or supercritical mass
Critical Mass

Critical Mass is a bicycling event typically held on the last Friday of every month in over 300 city around the world. While the ride was originally founded in 1992 with the idea of drawing attention to how unfriendly the city was to bicyclists, the leaderless structure of Critical Mass makes it impossible to assign it any one specific goal...
 will undergo.

In a uranium
Uranium

Uranium is a silvery-gray metallic chemical element in the actinide series of the periodic table that has the chemical symbol U and atomic number 92....
 graphite chain reacting pile the critical size
Critical Mass

Critical Mass is a bicycling event typically held on the last Friday of every month in over 300 city around the world. While the ride was originally founded in 1992 with the idea of drawing attention to how unfriendly the city was to bicyclists, the leaderless structure of Critical Mass makes it impossible to assign it any one specific goal...
 may be considerably reduced by surrounding the pile with a layer of graphite, since such an envelope reflects many neutrons back into the pile.






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A neutron reflector is any material that reflects neutron
Neutron

The neutron is a subatomic particle with no net electric charge and a mass slightly larger than that of a proton.Neutrons are usually found in atomic nucleus....
s. Usually, this term refers to the elastic scattering rather than to a specular reflection
Specular reflection

Specular reflection is the perfect, mirror-like reflection of light from a surface, in which light from a single incoming direction is reflected into a single outgoing direction....
. This reflector (scatterer) may be graphite
Graphite

The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Greek language ??afe?? : "to draw/write", for its use in pencils, where it is commonly called lead, as distinguished from the actual metallic element lead....
, beryllium
Beryllium

Beryllium is a chemical element with the symbol Be and atomic number 4.A Bivalent element, beryllium is found naturally only combined with other elements in minerals....
, or other materials. A neutron reflector can make an otherwise subcritical mass of fissile material critical, or increase the amount of nuclear fission that a critical or supercritical mass
Critical Mass

Critical Mass is a bicycling event typically held on the last Friday of every month in over 300 city around the world. While the ride was originally founded in 1992 with the idea of drawing attention to how unfriendly the city was to bicyclists, the leaderless structure of Critical Mass makes it impossible to assign it any one specific goal...
 will undergo.

In a uranium
Uranium

Uranium is a silvery-gray metallic chemical element in the actinide series of the periodic table that has the chemical symbol U and atomic number 92....
 graphite chain reacting pile the critical size
Critical Mass

Critical Mass is a bicycling event typically held on the last Friday of every month in over 300 city around the world. While the ride was originally founded in 1992 with the idea of drawing attention to how unfriendly the city was to bicyclists, the leaderless structure of Critical Mass makes it impossible to assign it any one specific goal...
 may be considerably reduced by surrounding the pile with a layer of graphite, since such an envelope reflects many neutrons back into the pile. A similar envelope can be used to reduce the critical size of a nuclear weapon
Nuclear weapon

A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either nuclear fission or a combination of fission and nuclear fusion....
, but here the envelope has an additional role: its very inertia
Inertia

File:192447main 017 law of inertia.oggInertia is the resistance of an object to a change in its state of motion. The principle of inertia is one of the fundamental principles of classical physics which are used to describe the Motion of matter and how it is affected by applied forces....
 delays the expansion of the reacting material. For this reason such an envelope is often called a tamper
Nuclear weapon design

Nuclear weapon designs are physical, chemical, and engineering arrangements that cause the physics package of a Nuclear weapons to detonate. There are three basic design types....
. As has already been remarked, the weapon tends to fly to bits as the reaction proceeds and this tends to stop the reaction, so the use of a tamper makes for a longer lasting, more energetic, and more efficient explosion. The most effective tamper is the one having the highest density; high tensile strength
Tensile strength

Tensile strength , or is the Stress at which a material breaks or permanently deforms. Tensile strength is an Intensive and extensive properties and, consequently, does not depend on the size of the test specimen....
 turns out to be unimportant because no material will hold together under the extreme pressures of a nuclear weapon. Coincidently, high density materials are excellent neutron reflectors. This makes them doubly suitable for nuclear weapons.

While the effect of a tamper is to increase the efficiency, both by reflecting neutrons and by delaying the expansion of the bomb, the effect on the critical mass is not as great as on the efficiency. The reason for this is that the process of reflection is relatively time consuming and may not occur extensively before the chain reaction is terminated.

See also

  • Nuclear weapon design
    Nuclear weapon design

    Nuclear weapon designs are physical, chemical, and engineering arrangements that cause the physics package of a Nuclear weapons to detonate. There are three basic design types....