Understanding Types of Natural Radioactive Decay

 Certain isotopes are unstable: Their nuclei break apart, undergoing nuclear decay. Sometimes the product of that nuclear decay is unstable itself and undergoes nuclear decay, too. For example, when uranium-238 (U-238) initially decays, it produces thorium-234 (Th-234), which decays to protactinium- 234 (Pa-234). The decay continues until, finally, after a total of 14 steps, lead-206 (Pb-206) is produced. Pb-206 is stable, and the decay sequence, or series, stops.

Before I show you how radioactive isotopes decay, first consider why a particular isotope decays. The nucleus has all those positively charged protons shoved together in an extremely small volume of space. All those protons are repelling each other. The forces that normally hold the nucleus together, the nuclear glue, sometimes can’t do the job, and so the nucleus breaks apart, undergoing nuclear decay.

The neutron/proton ratio for a certain element must fall within a certain range for the element to be stable. All elements with 84 or more protons are unstable; they eventually undergo decay. Other isotopes with fewer protons in their nucleus are also radioactive. The radioactivity corresponds to the neutron/ proton ratio in the atom. If the neutron/proton ratio is too high (there are too many neutrons or too few protons), the isotope is said to be neutron rich and is, therefore, unstable.

Likewise, if the neutron/proton ratio is too low (there are too few neutrons or too many protons), the isotope is unstable. That’s why some isotopes of an element are stable and others are radioactive.

Naturally occurring radioactive isotopes decay in three primary ways:

✓ Alpha particle emission

✓ Beta particle emission

✓ Gamma radiation emission

In addition, there are a couple of less common types of radioactive decay:

✓ Positron emission

✓ Electron capture