Historical clue formulations

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