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## Some heavy elements have unstable atomic nuclei that occasionally change their chemical identity by releasing particles or energy.

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Atomic Bomb

### Atomic Bomb

Credit: Charles Levy
Source: http://en.wikipedia.org/wiki/File:Nagasakibomb.jpg

A result of atomic fission, nuclear weapons have been and continue to be a source concern for everyone around the world. The mushroom cloud seen above at Nagasaki, Japan is the second of two atomic bombs dropped during WWII.

#### News You Can Use

• Fission is the process in which the nucleus of a particle splits into smaller lighter nuclei. This process results in the release of gamma rays and extraordinarily large amounts of energy. The large amounts of energy released in an atomic bomb blast are a result of a chain reaction that happens between several uranium-235 atoms and several neutrons.
• Credit: Federal Government of the United States
Source: http://en.wikipedia.org/wiki/File:Uk-grable2.jpg

Nuclear weapons test conducted by the United States (1953) [Figure2]

• When energetic free neutrons are absorbed by uranium-235 atoms the nucleus fissions into two atoms releasing neutrons as well as some energy that is equal to the binding energy. Some of the neutrons are lost while others will collide with other uranium-235 atoms. As a result, each time a uranium-235 atoms splits, free neutrons are released to split other uranium-235 atoms as well as large amounts of energy. This reaction can be seen in the following balanced equation:

\begin{align*}n + ^{235}U \rightarrow ^{141}BA + ^{92}Kr + 3n + energy\end{align*}

• While fission can be extremely dangerous, it also holds the potential for large amounts of usable energy. Many fission nuclear reactors use neutrons to produce fission to create an environment where there is a controlled amount of energy released. The amount of energy that can be harvested from nuclear fuel is a million times the amount of energy available in a similar mass of gasoline.

#### Explore More

Using the information provided above, answer the following questions.

1. Why is the mass before nuclear fission heavier than the mass after?
2. Why must the rate of the fission reaction in a nuclear reactor be controlled?
3. Is the energy produced from fission more or less dangerous than the energy produced from fusion?

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