Jeopardy! category: CHEMICAL ELEMENT PAIRS (10-2-2015)
$800 clue: The first 2 transuranium elements
The gist: Well, “trans-” means “beyond,” and “uranium” shares its name with something big.So the first two transuranium elements are neptunium and plutonium, their celestial namesakes being the two planets (until 2006) whose average distances from the sun are greater than that of Uranus. Uranium is special. It’s the heaviest element that occurs naturally on Earth, with stable isotopes having half-lives ranging from 69 to about 4.5 billion years. That last one, uranium-238, is the most common, and lasts long enough that we can still find it lying around despite the Earth’s 4.6 billion year age. Anything heavier than uranium, however, is too unstable to last as long as the Earth has, meaning that any bits of it that might have been put down when the Earth was born have long since decayed into something lighter. For example, Neptunium-237, that element’s stablest form, has a half-life of 2.14 million years, which sounds impressive to us short-lived humans but is less than 0.05% of the age of the Earth. Consequently, none of the transuranium elements have been discovered in nature – they have all been synthesized in particle accelerators or nuclear reactors (or detected after detonating atomic bombs), an honour that goes only to technetium (symbol Tc, number 43) among the pre-uranium elements. Currently, the transuraniums go up to atomic number 118, provisionally named “ununoctium,” which was synthesized by Russian scientists in 2002. Interestingly, it’s theorized based on extrapolations of nuclear stability that some isotopes of even heavier elements, perhaps somewhere above atomic number 120, may prove to have much longer half-lives, perhaps days or even years, in what’s known as the “island of stability.”
The clue: Although most Jeopardy! contestants probably know that Neptune and Pluto follow Uranus in the solar system, it’s probably pretty tough to make the connection to neptunium and plutonium if you’re not expecting it, and sure enough this one went as a Triple Stumper. Maybe a little tough for an $800 clue, even if it makes perfect sense in hindsight.
In Jeopardy!: Neptunium and plutonium in fact appear in eight clues together in the J!Archive, usually with the clue mentioning neptunium and the correct response being the better-known plutonium. Often the clear implication is for the contestants to think of the order of the planets (and dwarf planet), and in fact one other clue, a Daily Double!, is basically this clue plus an explicit mention of planets. By themselves, plutonium is much more common, appearing in 36 clues to neptunium’s ten.