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Answer to Question #2994 Submitted to "Ask the Experts"

Category: Radiation Basics — Elements

The following question was answered by an expert in the appropriate field:

Q
What is the very last naturally occurring element on the periodic table?
A

Uranium, with atomic number 92, is the last naturally occurring element on the periodic table. This is because all nuclides above atomic number 83 are radioactive (Turner 1995), and all above uranium that might have been present in Earth's early geological history have relatively short half-lives and have decayed away (Faure 1986). The reason that uranium is found naturally is that, even though radioactive, it has two isotopes (235U and 238U) with half-lives (700 million years and 4.5 billion years, respectively) that are on the order of Earth's age. A third naturally occurring uranium isotope, 234U, is formed as a result of radioactive decay of 238U.

You can get more information about naturally occurring radioactive materials at The TENORM Page and in the "Naturally Occurring Radioactive Material (NORM)" section on this Web site in Ask the Experts Environmental and Background Radiation Category.

James S. Bogard, PhD, CHP

References

Turner JE. Atoms, radiation and radiation protection. Second Edition: John Wiley & Sons, Inc.; 1995: 95-96.

Faure G. Principles of isotope geology. Second Edition: John Wiley & Sons, Inc.; 1986: 14-20.

Answer posted on 30 September 2003. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.
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