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#2001 Posted by deactivated-5b84aca03eae8 (6261 posts) - - Show Bio
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#2002 Posted by jagernutt (16340 posts) - - Show Bio
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#2004 Posted by deactivated-5b84aca03eae8 (6261 posts) - - Show Bio
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#2005 Posted by jagernutt (16340 posts) - - Show Bio
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#2006 Posted by deactivated-5b84aca03eae8 (6261 posts) - - Show Bio
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#2007 Posted by jagernutt (16340 posts) - - Show Bio
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#2008 Posted by deactivated-5b84aca03eae8 (6261 posts) - - Show Bio
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#2009 Posted by jagernutt (16340 posts) - - Show Bio
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#2010 Posted by jagernutt (16340 posts) - - Show Bio
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#2011 Posted by TheWatcherKing (18331 posts) - - Show Bio

New feeling: surprise. I lost them in my vastness. Only i foil me.

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#2012 Posted by jagernutt (16340 posts) - - Show Bio

New feeling: surprise. I lost them in my vastness. Only i foil me.

Chaos king. How might the mistress of Death be of service😎

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#2013 Edited by Enemybird (5106 posts) - - Show Bio

..............................................

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#2014 Posted by deactivated-5b84aca03eae8 (6261 posts) - - Show Bio

Trust is weakness.

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#2015 Posted by EmpressOfDread (12367 posts) - - Show Bio

I need to save the planet before I turn into the "Maiden of might" and start performing super feats in public, I will command my Linda Lee robot to take my place here.

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#2016 Posted by Rey_King (2421 posts) - - Show Bio

*Exists*

Humans get mutated

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#2017 Posted by deactivated-5b5405244e89c (8376 posts) - - Show Bio

Can't without getting banned :P

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#2018 Posted by deactivated-5b84aca03eae8 (6261 posts) - - Show Bio

The warriors I am needed for are no more.

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#2019 Posted by TheTruthIII (3309 posts) - - Show Bio

aaaaaaaaaaaaaaaaaaaaaaaaaAAAAAAAAAAA! YOU CAN'T SEE ME! (to the tune of Kamehameha) AAAATT-TIIII-TUDEEEE ADDDD-JUSTMENTTTTTTTT!

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#2020 Posted by jagernutt (16340 posts) - - Show Bio

I need to save the planet before I turn into the "Maiden of might" and start performing super feats in public, I will command my Linda Lee robot to take my place here.

Quick thinking

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#2021 Posted by MrDirector786 (44087 posts) - - Show Bio

The line of Primes has grown weak in my absence! And thus, you shall FALL!

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#2022 Posted by RampageTheFirst (7571 posts) - - Show Bio

I am not IMPRESSED!

Online
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#2023 Posted by EmpressOfDread (12367 posts) - - Show Bio

Mxyzptlk is here this time I will deal with him and finally show Clark that I can reveal myself to the world and get rid of that Linda Lee robot.

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#2024 Posted by jagernutt (16340 posts) - - Show Bio
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No Caption Provided

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#2025 Posted by deactivated-5b84aca03eae8 (6261 posts) - - Show Bio

It's none of my business really.

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#2026 Posted by deactivated-5c07a0327fd39 (4596 posts) - - Show Bio

I just orbit the Earth...

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#2027 Posted by deathstroke512 (2375 posts) - - Show Bio

I m batman.Wanna know my secret identity?Cause I m batman.

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#2028 Edited by Rey_King (2421 posts) - - Show Bio

In this symbolic representing of a nuclear reaction, lithium-6 (6

3Li) and deuterium (2

1H) react to form the highly excited intermediate nucleus 8

4Be which then decays immediately into two alpha particles of helium-4 (4

2He). Protons are symbolically represented by red spheres, and neutrons by blue spheres.

In nuclear physics and nuclear chemistry, a nuclear reaction is semantically considered to be the process in which two nuclei, or else a nucleus of an atom and a subatomic particle(such as a proton, neutron, or high energyelectron) from outside the atom, collide to produce one or more nuclides that are different from the nuclide(s) that began the process. Thus, a nuclear reaction must cause a transformation of at least one nuclide to another. If a nucleus interacts with another nucleus or particle and they then separate without changing the nature of any nuclide, the process is simply referred to as a type of nuclear scattering, rather than a nuclear reaction.

In principle, a reaction can involve more than two particlescolliding, but because the probability of three or more nuclei to meet at the same time at the same place is much less than for two nuclei, such an event is exceptionally rare (see triple alpha process for an example very close to a three-body nuclear reaction). "Nuclear reaction" is a term implying an induced change in a nuclide, and thus it does not apply to any type of radioactive decay(which by definition is a spontaneous process)[citation needed].

Natural nuclear reactions occur in the interaction between cosmic rays and matter, and nuclear reactions can be employed artificially to obtain nuclear energy, at an adjustable rate, on demand. Perhaps the most notable nuclear reactions are the nuclear chain reactions in fissionable materials that produce induced nuclear fission, and the various nuclear fusion reactions of light elements that power the energy production of the Sun and stars.

Nuclear reactions may be shown in a form similar to chemical equations, for which invariant mass must balance for each side of the equation, and in which transformations of particles must follow certain conservation laws, such as conservation of charge and baryon number (total atomic mass number). An example of this notation follows:

6
3Li
+2
1H
4
2He
+?.

To balance the equation above for mass, charge and mass number, the second nucleus to the right must have atomic number 2 and mass number 4; it is therefore also helium-4. The complete equation therefore reads:

6
3Li
+2
1H
4
2He
+4
2He
.

or more simply:

6
3Li
+2
1H
2 4
2He
.

Instead of using the full equations in the style above, in many situations a compact notation is used to describe nuclear reactions. This style of the form A(b,c)D is equivalent to A + b producing c + D. Common light particles are often abbreviated in this shorthand, typically p for proton, n for neutron, d for deuteron, α representing an alpha particle or helium-4, β for beta particle or electron, γ for gamma photon, etc. The reaction above would be written as Li-6(d,α)α.[1][2]

Contents

History

In 1919, Ernest Rutherford was able to accomplish transmutation of nitrogen into oxygen at the University of Manchester, using alpha particles directed at nitrogen 14N + α → 16O + p. This was the first observation of an induced nuclear reaction, that is, a reaction in which particles from one decay are used to transform another atomic nucleus. Eventually, in 1932 at Cambridge University, a fully artificial nuclear reaction and nuclear transmutation was achieved by Rutherford's colleagues John Cockcroft and Ernest Walton, who used artificially accelerated protons against lithium-7, to split the nucleus into two alpha particles. The feat was popularly known as "splitting the atom", although it was not the modern nuclear fission reaction later discovered in heavy elements, in 1938 by the German scientists Otto Hahn and Fritz Strassmann.[3]

Energy conservation

Kinetic energy may be released during the course of a reaction (exothermic reaction) or kinetic energy may have to be supplied for the reaction to take place (endothermic reaction). This can be calculated by reference to a table of very accurate particle rest masses,[4] as follows: according to the reference tables, the 6

3Li nucleus has a standard atomic weight of 6.015 atomic mass units (abbreviated u), the deuterium has 2.014 u, and the helium-4 nucleus has 4.0026 u. Thus:

  • the sum of the rest mass of the individual nuclei = 6.015 + 2.014 = 8.029 u;
  • the total rest mass on the two helium-nuclei = 2 × 4.0026 = 8.0052 u;
  • missing rest mass = 8.029 – 8.0052 = 0.0238 atomic mass units.

In a nuclear reaction, the total (relativistic) energy is conserved. The "missing" rest mass must therefore reappear as kinetic energy released in the reaction; its source is the nuclear binding energy. Using Einstein's mass-energy equivalence formula E = mc², the amount of energy released can be determined. We first need the energy equivalent of one atomic mass unit:

1 u = (1.66054 × 10−27 kg) × (2.99792 × 108 m/s)²
= 1.49242 × 10−10 kg (m/s)² = 1.49242 × 10−10 J (joule) × (1 MeV / 1.60218 × 10−13 J)
= 931.49 MeV,
so 1 u = 931.49 MeV.

Hence, the energy released is 0.0238 × 931 MeV = 22.2 MeV.

Expressed differently: the mass is reduced by 0.3%, corresponding to 0.3% of 90 PJ/kg is 270 TJ/kg.

This is a large amount of energy for a nuclear reaction; the amount is so high because the binding energy per nucleon of the helium-4 nucleus is unusually high, because the He-4 nucleus is "doubly magic". (The He-4 nucleus is unusually stable and tightly bound for the same reason that the helium atom is inert: each pair of protons and neutrons in He-4 occupies a filled 1snuclear orbital in the same way that the pair of electrons in the helium atom occupy a filled 1selectron orbital). Consequently, alpha particles appear frequently on the right hand side of nuclear reactions.

The energy released in a nuclear reaction can appear mainly in one of three ways:

  • kinetic energy of the product particles (fraction of the kinetic energy of the charged nuclear reaction products can be directly converted into electrostatic energy);[5]
  • emission of very high energy photons, called gamma rays;
  • some energy may remain in the nucleus, as a metastableenergy level.

When the product nucleus is metastable, this is indicated by placing an asterisk ("*") next to its atomic number. This energy is eventually released through nuclear decay.

A small amount of energy may also emerge in the form of X-rays. Generally, the product nucleus has a different atomic number, and thus the configuration of its electron shells is wrong. As the electrons rearrange themselves and drop to lower energy levels, internal transition X-rays (X-rays with precisely defined emission lines) may be emitted.

Q-value and energy balanc

In writing down the reaction equation, in a way analogous to a chemical equation, one may in addition give the reaction energy on the right side:

Target nucleus + projectile → Final nucleus + ejectile + Q.

For the particular case discussed above, the reaction energy has already been calculated as Q = 22.2 MeV. Hence:

6
3Li
+2
1H
2 4
2He
+22.2 MeV.

The reaction energy (the "Q-value") is positive for exothermal reactions and negative for endothermal reactions. On the one hand, it is the difference between the sums of kinetic energies on the final side and on the initial side. But on the other hand, it is also the difference between the nuclear rest masses on the initial side and on the final side (in this way, we have calculated the Q-value above).

Reaction rates

If the reaction equation is balanced, that does not mean that the reaction really occurs. The rate at which reactions occur depends on the particle energy, the particle flux and the reaction cross section. An example of a large repository of reaction rates is the REACLIB database, as maintained by the Joint Institute for Nuclear Astrophysics.

Neutrons vs. ions

In the initial collision which begins the reaction, the particles must approach closely enough so that the short range strong force can affect them. As most common nuclear particles are positively charged, this means they must overcome considerable electrostatic repulsionbefore the reaction can begin. Even if the target nucleus is part of a neutral atom, the other particle must penetrate well beyond the electron cloud and closely approach the nucleus, which is positively charged. Thus, such particles must be first accelerated to high energy, for example by:

Also, since the force of repulsion is proportional to the product of the two charges, reactions between heavy nuclei are rarer, and require higher initiating energy, than those between a heavy and light nucleus; while reactions between two light nuclei are the most common ones.

Neutrons, on the other hand, have no electric charge to cause repulsion, and are able to initiate a nuclear reaction at very low energies. In fact, at extremely low particle energies (corresponding, say, to thermal equilibrium at room temperature), the neutron's de Broglie wavelength is greatly increased, possibly greatly increasing its capture cross section, at energies close to resonances of the nuclei involved. Thus low-energy neutrons may be even more reactive than high energy neutrons.

Notable types

While the number of possible nuclear reactions is immense, there are several types which are more common, or otherwise notable. Some examples include:

  • Fusion reactions — two light nuclei join to form a heavier one, with additional particles (usually protons or neutrons) emitted subsequently.
  • Spallation — a nucleus is hit by a particle with sufficient energy and momentum to knock out several small fragments or smash it into many fragments.
  • Induced gamma emission belongs to a class in which only photons were involved in creating and destroying states of nuclear excitation.
  • Alpha decay — Though driven by the same underlying forces as spontaneous fission, α decay is usually considered to be separate from the latter. The often-quoted idea that "nuclear reactions" are confined to induced processes is incorrect. "Radioactive decays" are a subgroup of "nuclear reactions" that are spontaneous rather than induced. For example, so-called "hot alpha particles" with unusually high energies may actually be produced in induced ternary fission, which is an induced nuclear reaction (contrasting with spontaneous fission). Such alphas occur from spontaneous ternary fission as well.
  • Fission reactions — a very heavy nucleus, after absorbing additional light particles (usually neutrons), splits into two or sometimes three pieces. This is an induced nuclear reaction. Spontaneous fission, which occurs without assistance of a neutron, is usually not considered a nuclear reaction. At most, it is not an induced nuclear reaction.

Direct reactions

An intermediate energy projectile transfers energy or picks up or loses nucleons to the nucleus in a single quick (10−21 second) event. Energy and momentum transfer are relatively small. These are particularly useful in experimental nuclear physics, because the reaction mechanisms are often simple enough to calculate with sufficient accuracy to probe the structure of the target nucleus.

Inelastic scatteringEdit

Main article: Inelastic scattering

Only energy and momentum are transferred.

  • (p,p') tests differences between nuclear states.
  • (α,α') measures nuclear surface shapes and sizes. Since α particles that hit the nucleus react more violently, elastic and shallow inelastic α scattering are sensitive to the shapes and sizes of the targets, like light scattered from a small black object.
  • (e,e') is useful for probing the interior structure. Since electrons interact less strongly than do protons and neutrons, they reach to the centers of the targets and their wave functions are less distorted by passing through the nucleus.

Transfer reactions

Usually at moderately low energy, one or more nucleons are transferred between the projectile and target. These are useful in studying outer shell structure of nuclei.

  • (α,n) and (α,p) reactions. Some of the earliest nuclear reactions studied involved an alpha particle produced by alpha decay, knocking a nucleon from a target nucleus.
  • (d,n) and (d,p) reactions. A deuteronbeam impinges on a target; the target nuclei absorb either the neutron or proton from the deuteron. The deuteron is so loosely bound that this is almost the same as proton or neutron capture. A compound nucleus may be formed, leading to additional neutrons being emitted more slowly. (d,n) reactions are used to generate energetic neutrons.
  • The strangeness exchange reaction (K, π) has been used to study hypernuclei.
  • The reaction 14N(α,p)17O performed by Rutherford in 1917 (reported 1919), is generally regarded as the first nuclear transmutationexperiment.

Reactions with neutrons

T7Li14C
(n,α)6Li + n → T + α10B + n → 7Li + α17O + n → 14C + α21Ne + n → 18O + α37Ar + n → 34S + α
(n,p)3He + n → T + p7Be + n → 7Li + p14N + n → 14C + p22Na + n → 22Ne + p

Reactions with neutrons are important in nuclear reactors and nuclear weapons. While the best-known neutron reactions are neutron scattering, neutron capture, and nuclear fission, for some light nuclei (especially odd-odd nuclei) the most probable reaction with a thermal neutron is a transfer reaction:

Some reactions are only possible with fast neutrons:

Compound nuclear reactions

Either a low-energy projectile is absorbed or a higher energy particle transfers energy to the nucleus, leaving it with too much energy to be fully bound together. On a time scale of about 10−19 seconds, particles, usually neutrons, are "boiled" off. That is, it remains together until enough energy happens to be concentrated in one neutron to escape the mutual attraction. Charged particles rarely boil off because of the coulomb barrier. The excited quasi-bound nucleus is called a compound nucleus.

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#2029 Posted by deactivated-5b84aca03eae8 (6261 posts) - - Show Bio

^What the heck did I just read lol?

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#2030 Posted by deactivated-5b84aca03eae8 (6261 posts) - - Show Bio

I'm a Destroyer deity and I take no sides in battles.

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#2031 Posted by removekebab (3790 posts) - - Show Bio
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#2033 Posted by deactivated-5b84aca03eae8 (6261 posts) - - Show Bio

I'm the one who gripped you tight and raised you from perdition.

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#2034 Posted by deactivated-5b9c488ed7f76 (10909 posts) - - Show Bio

My spider sense is tingling hehe

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#2035 Posted by TheWatcherKing (18331 posts) - - Show Bio

Heroes and villains both thrive on violence, but we're still categorized. "You're good." "You're evil." That's how it is!! Symbol of peace? Hah!! In the end you're just a tool for violence, made to keep us down! And violence only breeds more violence.

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#2036 Posted by deactivated-5b84aca03eae8 (6261 posts) - - Show Bio

I'm an Angel of the Lord.

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#2038 Posted by Gripper (2603 posts) - - Show Bio

Bring me the head of Spider-Man!

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#2039 Edited by TheWatcherKing (18331 posts) - - Show Bio

Proud mother Gaea....still dreaming of creation?Return to my night.

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#2040 Posted by SaintWildcard (21794 posts) - - Show Bio

Looks like somebody wants a knife fight... Someone I'm looking at

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#2041 Posted by deactivated-5b9c488ed7f76 (10909 posts) - - Show Bio
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#2042 Posted by deactivated-5b60e98a8eb99 (11593 posts) - - Show Bio

Supaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaah

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#2043 Posted by LEGACY6364 (7441 posts) - - Show Bio

I am the whisper in the winds of chaos! I kindle the flames of terror!

I am the shroud that strides in the shadows!

I am Leviathan, beast of all beast! And I shall deliver true terrors upon this thread!

Said is my power!

Such is my will!

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#2044 Posted by deactivated-5b2121a0a9a00 (10000 posts) - - Show Bio

BOI

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#2045 Posted by Gripper (2603 posts) - - Show Bio

Must Kill Spider-Man

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#2046 Posted by deactivated-5bf470b432518 (5801 posts) - - Show Bio

You're intellectually inferior half wits.

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#2047 Posted by JakeFuryV2 (3106 posts) - - Show Bio

Thwip thwip.

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#2048 Posted by Lucid_Dream (96 posts) - - Show Bio

it's just a prank bro

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#2049 Posted by Mutant1230 (6487 posts) - - Show Bio

Hey, cool Comic Vine kids. Listen, if any of are feeling angry about superheroes or puberty, anything like that, just come talk to me in my office. I'm your friend, and I'm here to help.

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#2050 Posted by Spinach (263 posts) - - Show Bio

nom nom nom