actinium series


: a radioactive series beginning with actinouranium, constituting the isotope of uranium of mass number 235, and ending with actinium D, constituting the nonradioactive isotope of lead of mass number 207: actinouranium, atomic number 92 (synonym uranium 235) → uranium Y, atomic number 90 (synonym thorium 231) → protactinium 231, atomic number 91 → actinium 227, atomic number 89 → radioactinium, atomic number 90 (synonym thorium 227) [or actinium K, atomic number 87 (synonym francium 223)] → actinium X, atomic number 88 (synonym radium 223) → actinon, atomic number 86 (synonym radon 219) → actinium A, atomic number 84 (synonym polonium 215) → actinium B, atomic number 82 (synonym lead 211) [or astatine 215, atomic number 85] → actinium C, atomic number 83 (synonym bismuth 211) → actinium C, atomic number 84 (synonym polonium 211) [or actinium C, atomic number 81 (synonym thallium 207)] → actinium D, atomic number 82 (synonym lead 207) compare actinide series

Word History

First Known Use

1906, in the meaning defined above

Time Traveler
The first known use of actinium series was in 1906

Love words?

You must — there are over 200,000 words in our free online dictionary, but you are looking for one that’s only in the Merriam-Webster Unabridged Dictionary.

Start your free trial today and get unlimited access to America's largest dictionary, with:

  • More than 250,000 words that aren't in our free dictionary
  • Expanded definitions, etymologies, and usage notes
  • Advanced search features
  • Ad free!

Dictionary Entries Near actinium series

Cite this Entry

“Actinium series.” Dictionary, Merriam-Webster, Accessed 12 Apr. 2024.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!