Radioactive Decay

Each radioactive isotope will continue to undergo radioactive decay into other isotopes until it is stable (e.g., no longer radioactive). Some isotopes will only need to go through a few decay steps to become stable, while others will go through many radioactive decay steps to become stable. Uranium-238, for example, will undergo 14 radioactive decays to eventually become lead-206 which is stable and no longer radioactive. Some of these radioactive decays will be alpha decays and some of these decays will be beta decays.

As uranium-238 decays into lead-206, it will sometimes decay into a different isotope of its parent uranium isotope and sometimes it will decay into an isotope of a totally different element than its parent. This series of alpha and beta decays is known as the uranium-238 decay series..

Uranium-238 Decay Series
Radioactive Isotope
Half Life
Type of Decay
Uranium-238
4.5 billion years
α
Thorium-234
24 days
β
Protactinium-234
1.2 minutes
β
Uranium-234
245,000 years
α
Thorium-230
75,000 years
α
Radium-226
1,600 years
α
Radon-222
3.8 days
α
Polonium-218
3.1 minutes
α
Lead-214
27 minutes
β
Bismuth-214
20 minutes
β
Polonium-214
0.00016 seconds
α
Lead-210
22 years
β
Bismuth-210
5 days
β
Polonium-210
138 days
α
Lead-206
(stable)

Each radioactive isotope is the parent of the progeny isotope listed below it. Each progeny isotope has a much shorter half-life than uranium-238. This radioactive series will require a little over 6.5 billion years to complete.