Isotope Naming Convention

I read George B. Kauffman’s article “Celebrating the Isotope” with great interest, as I did not know most of this history (C&EN, Dec. 2, 2013, page 30). However, there are some confusing statements in the article. It is conventional when naming isotopes (and not using chemical symbols, an example being ²³⁸U) to fully spell out the name of the element and then put the mass number after the name, such as uranium-238. A name like Kauffman uses, uranium-92, where the atomic number is used, is redundant and does not state which isotope of uranium is being discussed.

Kauffman mentions two radioactive decay series: those “beginning with uranium-92 and thorium-90, with lead-82 being the final product of both series.” True, but not the complete story: The final product of the decay series of uranium-238 is stable lead-206, and the final product of the decay series of thorium-232 is stable lead-208. Since naturally occurring thorium is almost 100% thorium-232, I presume it is the isotope being referred to. A very clear discussion of these decay series can be found at http://bit.ly/1f50tav.

Also, Kauffman says that Frederick Soddy and Ernest Rutherford predicted that helium should be “the decay product of radium-88.” The actual story is this: In the uranium-238 decay series, radium-226 is produced and then decays by giving off an α-particle (He nucleus). However, during the decay series of thorium-232, two isotopes of radium are formed: radium-228, which decays by β-(negative electron) emission, and radium-224, which decays by α-emission.

Harvey F. Carroll
Lake Forest Park, Wash.