ISOTOPE
| Date | Clue |
|---|---|
| 2024-12-07 | Part of a nuclear family? |
| 2013-10-24 | Uranium 235, e.g. |
| 2011-05-03 | Member of a fictional Springfield baseball team |
| 2008-04-24 | Elemental form |
| 2005-12-26 | Heavy hydrogen, e.g. |
| 2004-05-14 | Elemental form |
| 2004-03-17 | Chemical relative |
| 2003-08-28 | Chemist's study |
| 2002-06-09 | Carbon-14, e.g. |
| 2001-07-15 | Heavy hydrogen, e.g. |
| 1999-03-28 | Element form |
| 1999-02-16 | U-235 or C-14, e.g. |