In nuclear fission, when a
stable nucleus is bombarded by particles, it breaks into two unequal lighter nuclei. Energy
is released in the process (exothermic process) and there is an
emission of neutrons.
Neutrons are good projectiles in this
reaction, as because they have no charge they are less repelled by the
nucleus. Neutrons emitted by fission are fast neutrons and with high
energy levels of around 1 MeV. They can become slow neutrons or thermal
neutrons, with an energy level of 1 eV, if they lose part of
their energy by colliding with the particles of a moderator.
The energy of a slow neutron is enough to split U-235 into two unequal
parts.
The massive nuclei when split produce two new elements.
These nuclei tend to have mass numbers of between 50 and 82.
You can see an animated diagram of a nuclear fission reaction here.
The process can be described in two stages:
| Capturing the neutron |
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| The process of fission |
 |
The nuclear fission reaction
is extremely useful because:
1.- A great deal of energy is released
2.- The process is self-perpetuating. The release of neutrons, two or
three per split nucleus (about 2.5 on average), means that these can
provoke more fission when they collide with other nuclei giving rise to
a chain reaction.
The problems associated with the use of fission are also considerable.
