Types of nuclear reactions
Three types of nuclear reactions Any change in the nucleus of an element is done via a nuclear reaction. The change may be due to radioactivity when a nucleus changes spontaneously or it may be the result of an interaction between two nuclei. In either case, we use a nuclear equation to represent the process. In general, there are three categories of nuclear reactions:
  1. spontaneous reactions,
  2. fission reactions, and
  3. fusion reactions.
The rules for writing and balancing the equations for these reactions are the same. Read the text aloud
Decay and spontaneous reactions The decay of a nucleus happens spontaneously. It is characterized by the half-life of the process and it is described by a nuclear equation. An example of a spontaneous reaction is the decay of the isotope americium-235, which decays by emitting an alpha particle according to the equation Read the text aloud
Am 95 240 → N 93 236 p+ H 2 4 e
Americium alpha decay
Alpha decay in a smoke detector This reaction is used as the basis for smoke detector systems. In the presence of smoke, the alpha particle that is emitted by this decay interacts with the smoke particles, which it ionizes. The ionized particles in turn create a current that is detected by electronics, triggering the audible or visual indicators of the alarm. The alpha radiation emitted by the smoke detectors do not present any health hazards under normal operating conditions, but the devices must be disposed of properly. Read the text aloud
Fission reactions break apart a large nucleus In a fission reaction, the nucleus breaks apart not spontaneously but as a result of an interaction with another particle. Although the nucleus of uranium-235 is an alpha-emitter (with a half-life of 704 million years), when it is bombarded by neutrons with enough energy the nucleus can also be broken apart in a fission reaction. The equation that represents this reaction is
n 0 1 + U 92 235 → X 54 140 e+ S 38 94 r+ n 0 1 + n 0 1
Uranium-235 fission reaction
Notice that there is one free neutron on the left-hand side but two neutrons on the right-hand side. This observation is the basis for nuclear energy generation and we will discuss it later in this chapter. Read the text aloud
Fusion reactions combine two nuclei The nuclear reaction by which two light nuclei combine to create a heavier nucleus is called a fusion reaction. An example of this process occurs in the core of the Sun, which produces energy by combining nuclei with low atomic numbers. A typical fusion reaction that combines two isotopes of hydrogen, deuterium ( H 1 2 ) and tritium ( H 1 3 ), is Read the text aloud
H 1 2 + H 1 3 → H 2 4 e+ n 0 1
Deuterium–tritium fusion reaction
This fusion reaction releases a large amount of energy, as can be seen from the plot of binding energy per nucleon. In general, the energy released from fusion reactions is much larger than the energy released from fission reactions. For this reason (and because of some other advantages of fusion over fission), fusion is considered a promising energy source for the future. Read the text aloud
Test your knowledge In a nuclear fusion reaction, hydrogen-2 and hydrogen-3 combine. This produces a different atom and a neutron. What is the atom produced?
  1. hydrogen-4
  2. hydrogen-5
  3. helium-4
  4. lithium-6
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