ISOTOPES
| Date | Clue |
|---|---|
| 2016-08-14 | Uranium 238 and strontium 90 |
| 2016-05-11 | Deuterium and tritium |
| 2011-11-28 | Springfield's minor-league team on "The Simpsons" |
| 2011-06-03 | Chemist's relatives? |
| 2010-05-05 | Carbon 14 and uranium 235 |
| 2005-03-01 | Deuterium and tritium, to hydrogen |
| 2000-07-10 | Some are radioactive |
| 1996-06-04 | Atoms with the same number of protons |
| 1995-09-25 | Carbon 14 and others |