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50 free Plutonium trivia questions with answers — science & nature quiz, new questions added Aug 2026.
This plutonium trivia quiz covers element 94 from the Berkeley cyclotron in 1940 to the power packs still running the Voyager probes. The easy questions handle the basics: the symbol, the atomic number, the planet it was named for, the bomb it fuelled and the spacecraft it powers. From there it moves through the physics and chemistry: six allotropes, the strange melting behaviour, gallium alloys, plutonium-239 versus plutonium-240, half-lives and what makes a sample weapons-grade. The harder half is for science and history buffs: Fermi's phantom 'hesperium', the name Seaborg almost chose, the X-10 reactor and Hanford's 'Queen Mary' buildings, Thin Man versus Fat Man, the Urchin initiator, the demon core, the human injection experiments, Rocky Flats, PUREX and MOX fuel, and the plutonium pacemakers still ticking in 2007. If you enjoyed our periodic table or Manhattan Project quizzes, this is the deep dive on one element. Every answer was checked against the encyclopaedia entry for plutonium before publishing.
30 of 50 questions with answers and explanations. Play the quiz
Q 01What is plutonium's chemical symbol?
Pu
Glenn Seaborg reportedly chose the letters as a joke on the interjection 'P U' for a bad smell.
Q 02What is plutonium's atomic number?
94
It is the element with the highest atomic number known to occur in nature.
Q 03Plutonium was named after which body, which was considered a planet at the time?
Pluto
Uranium and neptunium had been named after the two preceding planets.
Q 04Where was plutonium first synthesised, in 1940-41?
Berkeley, California
The University of California team bombarded uranium-238 with deuterons in the 60-inch cyclotron.
Q 05Which chemist led the team that first produced and identified plutonium?
Glenn T. Seaborg
McMillan, Segrè, Kennedy and Wahl were the other members.
Q 06Why was publication of the discovery delayed until 1948?
Wartime secrecy
The paper had been sent to Physical Review in March 1941.
Q 07Seaborg originally considered what alternative name for the element?
Plutium
'Ultimium' and 'extremium' were also floated by others, in the mistaken belief it was the last possible element.
Q 08Enrico Fermi's team wrongly claimed to have discovered element 94 in 1934 and gave it what name?
Hesperium
The sample actually contained fission products, mainly barium and krypton, since fission was still unknown.
Q 09How many allotropes does plutonium normally exhibit?
Six
A seventh, zeta, forms at high temperature within a limited pressure range.
Q 10In moist air, plutonium's oxides and hydrides can expand a sample by up to how much?
70%
The flaking powder is pyrophoric, igniting spontaneously in air.
Q 11What is plutonium's melting point?
640 °C
Its boiling point is an unusually high 3,228 °C, giving a huge liquid range.
Q 12Unusually, what happens to plutonium's density when it melts?
It increases by 2.5%
The liquid also has very high viscosity and surface tension for a metal.
Q 13Alloying plutonium with a small amount of which metal stabilises the soft delta phase at room temperature?
Gallium
Aluminium or cerium also work; the delta form is roughly as strong and malleable as aluminium.
Q 14Which isotope of element 94 is the main fissile one used in weapons and reactors?
Q 21How many plutonium-powered pacemakers were reported still implanted in US patients by the end of 2007?
Nine
There had been between 50 and 100 in 2003; lithium cells replaced them.
Q 22One kilogram of plutonium-238 generates roughly how much heat?
570 watts
A sheet of paper is enough to shield against its alpha particles.
Q 23The natural fission reactor at Oklo, where trace plutonium-239 occurs, is in which country?
Gabon
It forms when uranium-238 captures neutrons from other spontaneously fissioning uranium atoms.
Q 24Plutonium-244 has a half-life of about how long, the longest of any transuranic nuclide?
Pu-239
Uranium-233 and uranium-235 are the other two primary fissile isotopes.
Q 15What is the half-life of plutonium-239?
24,100 years
A 5 kg mass produces about 9.68 watts of heat from alpha decay.
Q 16Fission of one kilogram of plutonium-239 can release an explosion equivalent to how much TNT?
21,000 tons
That energy is what makes it useful in both bombs and reactors.
Q 17Which isotope's high spontaneous fission rate limits a sample's usefulness in weapons?
Pu-240
Its percentage determines whether plutonium is weapons-grade, fuel-grade or reactor-grade.
Q 18Weapons-grade plutonium contains less than what percentage of plutonium-240?
7%
Fuel-grade is 7-19% and reactor-grade 19% or more; 'supergrade' below 4% is used in US Navy weapons.
Q 19Plutonium-238 is used as a heat source in what kind of device on spacecraft?
Radioisotope thermoelectric generators
Its 87.7-year half-life and alpha emission make it warm enough to glow red hot without cooling.
Q 20Which pair of 1977 spacecraft carry plutonium-238 power sources that started at 500 watts each?
The Voyagers
Three decades after launch, each RTG still produced about 300 watts, and both probes were operating into the 2020s.
80 million years
Evidence of its former presence in the early Solar System has been found in meteorites.
Q 25Plutonium has been detected in the spectrum of which chemically peculiar celestial object?
Przybylski's Star
Astrophysical detection of the element is otherwise extremely limited.
Q 26Roughly how many atmospheric and underwater nuclear tests left plutonium traces in most humans?
550
Most such testing ended with the 1963 Limited Test Ban Treaty, though France continued until 1974 and China until 1980.
Q 27The first self-sustaining chain reaction, CP-1, was achieved in December 1942 under a football grandstand in which city?
Chicago
Fermi's graphite-and-uranium pile sat on a racket court under Stagg Field's west stands.
Q 28Where was the Manhattan Project's main plutonium production facility?
Hanford, Washington
Oak Ridge did uranium enrichment and Los Alamos designed the weapons.
Q 29What was the first production pile to make plutonium-239, which went online at Oak Ridge in 1943?
X-10 Graphite Reactor
It was built at Oak Ridge; the industrial-scale Hanford B Reactor followed in 1945.
Q 30Workers nicknamed the huge canyon-like plutonium separation buildings at Hanford after what?
The Queen Mary
They were 800 feet long and operators worked behind seven feet of concrete using periscopes and TV monitors.