During the beginning of the twentieth century, many radioactive substances were discovered, the properties of radiation were investigated and quantified, and a solid understanding of radiation and nuclear decay was developed.

The spontaneous change of an unstable nuclide into another is radioactive decay.

The loss of an inner shell electron leaves a vacancy that will be filled by one of the outer electrons.

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Figure 3 summarizes these types of decay, along with their equations and changes in atomic and mass numbers.

Positron emission tomography (PET) scans use radiation to diagnose and track health conditions and monitor medical treatments by revealing how parts of a patient’s body function (Figure 4).

The unstable nuclide is called the parent nuclide; the nuclide that results from the decay is known as the daughter nuclide.

The daughter nuclide may be stable, or it may decay itself.

Beta (β) decay is the emission of an electron from a nucleus.

Iodine-131 is an example of a nuclide that undergoes β decay: Beta decay, which can be thought of as the conversion of a neutron into a proton and a β particle, is observed in nuclides with a large n:p ratio.

We classify different types of radioactive decay by the radiation produced. Alpha particles, which are attracted to the negative plate and deflected by a relatively small amount, must be positively charged and relatively massive.

Beta particles, which are attracted to the positive plate and deflected a relatively large amount, must be negatively charged and relatively light.

Cobalt-60 emits γ radiation and is used in many applications including cancer treatment: Positron emission is observed for nuclides in which the n:p ratio is low. Positron decay is the conversion of a proton into a neutron with the emission of a positron.