How to Determine a High Neutron to Proton Ratio
The protons and neutrons in an atom's nucleus are held together by the strong nuclear force, which overpowers the electromagnetic force that protons exert on each other. Atoms with low atomic numbers tend to only need approximately as many neutrons as protons to remain stable. Atoms with larger atomic numbers need more neutrons to be stable, but if they have too many, they undergo beta decay. A large neutron-to-proton ratio results in the emission of an electron from the nucleus, which transforms one of the neutrons into a proton. Many things impact an atom's stable neutron-to-proton ratio, but it generally increases from 1 in the elements with smaller atomic numbers to approximately 1.5 for the elements with larger atomic numbers.
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Instructions
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Determine the number of protons in the atom. The number of protons is equivalent to the atom's atomic number. For example, carbon-14 has an atomic number of 6, according to the periodic table. Therefore, all atoms of carbon have 6 protons.
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Determine the number of neutrons in the atom. This is found by subtracting the atomic number (which is the number of protons) from the mass number. For example, carbon-14 has a mass number of 14. Therefore, it has 14 - 6 = 8 neutrons in its nucleus.
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Divide the number of neutrons by the number of protons to calculate the neutron-to-proton ratio. For example, carbon-14's neutron-to-proton ratio is 8/6 = 1.33.
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Determine if the neutron-to-proton ratio is too high for the nucleus to be stable. This depends on the element's atomic number and other factors. In general, atoms with low atomic numbers tend to be unstable if this ratio is more than 1. Atoms with middle-sized atomic numbers tend to be unstable if this ratio is more than 1.3. Atoms with large atomic numbers tend to be unstable if this ratio is more than 1.5. Because carbon-14 has a low atomic number and a neutron-to-proton ratio of 1.33, it undergoes beta decay.
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Tips & Warnings
All elements with atomic numbers above 83, or with more than 126 neutrons, are unstable and undergo some form of radioactive decay, often alpha-decay.
Elements with low neutron-to-proton ratios tend to undergo electron capture or positron emission to convert protons to neutrons.
References
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