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.