Isotopes

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Figure 1
Figure 1
Figure 2 There are three isotopes of hydrogen that differ only in the number of neutrons they possess. The hydrogen isotope has only one proton, the deuterium isotope has one proton and one neutron, and the tritium isotope has one proton and two neutrons.
Figure 2 There are three isotopes of hydrogen that differ only in the number of neutrons they possess. The hydrogen isotope has only one proton, the deuterium isotope has one proton and one neutron, and the tritium isotope has one proton and two neutrons.
Figure 3 Decay chain of isotope of uranium-238.
Figure 3 Decay chain of isotope of uranium-238.

To make atoms electrically neutral, all that is required is that the number of protons and electrons be equal. The number of neutrons, however, can change, so it is possible for two atoms to have a different number of neutrons for the same number of protons (different A, but same P). These different atoms of the same element are known as isotopes. Uranium and hydrogen, the heaviest and lightest of all the naturally-occurring elements and the fuel of choice for nuclear fission and fusion reactions, are both found naturally in three isotopes. Figure 2 shows the three isotopes of hydrogen.

The numbers in parenthesis give the relative abundance of the natural occurrence of each isotope. Since different isotopes are only different in the number of neutral charges they contain, they are chemically identical. As we will see, these isotopes may have significantly different nuclear characteristics. Radioactive materials are those isotopes which have unstable atomic nuclei and may undergo spontaneous decay, forming lighter isotopes (called daughters) and releasing highly energetic ionizing radiation in the process. For example, the isotope of uranium-238 decays into several isotopes before it becomes stable lead (Figure 3).

All elements with atomic masses heavier than bismuth are naturally radioactive. It is, however, possible to artificially produce isotopes of lighter elements. Half-life is an important quantity in measuring the effect of harmful radiation from a radioactive source.

References

(1) Toossi Reza, "Energy and the Environment:Sources, technologies, and impacts", Verve Publishers, 2005

Further Reading

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