48 Fun Facts About Uranium

What is uranium's atomic number?

Its symbol is U and it sits in the actinide series; it is the highest-numbered element found naturally in significant amounts.

Which astronomer discovered Uranus, the planet uranium is named after?

Herschel. William Herschel spotted it from his garden in Bath in 1781 and tried to name it George's Star after King George III, but the name did not stick.

Which chemist is credited with discovering uranium in 1789?

Martin Heinrich Klaproth. The Berlin chemist believed the black powder he had made was the new metal itself; it was only an oxide, and pure uranium was not isolated for another half-century.

In which mineral was uranium first discovered?

Pitchblende. The heavy black ore turned out to be more radioactive than the uranium in it could explain, and chasing that puzzle led to the discovery of two more new elements.

Whose signed letter of 1939 warned President Roosevelt that uranium could be turned into extremely powerful bombs?

Albert Einstein. The warning was really Leo Szilard's idea: he drafted it and had himself driven out to Einstein's Long Island holiday cottage for the one signature a president could not ignore.

Who discovered radioactivity in 1896 using a uranium salt left on a photographic plate?

Henri Becquerel. He was testing whether light made uranium salts give off rays, but a plate shut away in a dark drawer fogged all the same, so the rays had to come from the uranium itself.

Who coined the word 'radioactivity' while studying the rays given off by uranium?

Marie Curie. She took uranium's puzzling rays as the subject of her doctorate, found that thorium gave them off too, and needed a name for a property that clearly was not unique to one element.

Which uranium isotope is fissile and used in reactors and weapons?

U-235. Nobody could be sure which isotope did the splitting until 1940, when a Minnesota physicist separated a speck of it in a machine he had built himself and tests proved it was the one.

What is the half-life of uranium-238?

About 4.5 billion years. That is close to the age of the Earth itself, so roughly half the uranium-238 the planet started with is still here, which lets geologists date the very oldest rocks.

Uranium's density is about 70% higher than that of which metal?

Lead. Uranium is nearly as dense as gold, which is why the depleted metal makes a radiation shield that does the job in less space than lead itself.

Which two scientists found barium among the products of bombarding uranium with neutrons in 1938?

Otto Hahn and Fritz Strassmann. As chemists they hesitated to announce something physics said was impossible, since barium is barely half the weight of uranium, and wrote to an exiled colleague for help.

Who published the physical explanation of uranium's splitting in February 1939, naming it 'nuclear fission'?

Lise Meitner and Otto Robert Frisch. Aunt and nephew worked it out in Sweden, where she had fled from Nazi Germany, yet the Nobel Prize for fission went to her old Berlin partner alone.

Which physicist led the team that achieved the first self-sustaining nuclear chain reaction, in Chicago in 1942?

Enrico Fermi. The news was phoned through in code as 'the Italian navigator has just landed in the New World'; he had left Mussolini's Italy only four years before.

Which secret wartime city was built to enrich uranium for the Manhattan Project?

Oak Ridge. The secret city in the Tennessee hills soon outgrew its planners' estimates and held about 75,000 people by 1945.

What kind of vessel became the first to put to sea under nuclear power, in 1955?

A submarine. USS Nautilus signalled 'Underway on nuclear power' as she left harbour, and a reactor that needs no air let her stay submerged at speed for long stretches.

Chicago Pile-1, the first man-made nuclear reactor, was built in 1942 beneath what?

A football stadium's stands. The team stacked their graphite and uranium in a rackets court under the University of Chicago's Stagg Field, with no radiation shielding at all.

Which nuclear weapon, dropped on Hiroshima, relied on uranium fission?

Little Boy. It worked by firing one piece of uranium down a gun barrel into another, a design so wasteful that less than 2% of its uranium actually fissioned.

What term describes the smallest amount of uranium-235 that can sustain a chain reaction?

Critical mass. In any smaller lump too many neutrons escape for the reaction to keep going, which is why the Hiroshima bomb held its uranium in two separate pieces until the last instant.

Which Nobel-winning physicist was the scientific head of Nazi Germany's 'Uranium Club' nuclear project?

Werner Heisenberg. His team never got a chain reaction going, partly because a faulty measurement on impure samples convinced the Germans that graphite would not work in a reactor.

In 1951 the first electricity ever generated by a nuclear reactor was just enough to power what?

Four light bulbs. Idaho's Experimental Breeder Reactor I lit them on 20 December 1951 and was soon powering its whole building; four years later a sister reactor lit the nearby town of Arco.

Which country, beating Britain and America, opened the first nuclear power station to feed a public grid, in 1954?

Soviet Union. Its small Obninsk plant, southwest of Moscow, fed five megawatts to the grid, and its graphite-and-water design became the prototype for the reactors later built at Chernobyl.

What did French scientists discover in 1972 in the uranium ore at Oklo, in Gabon?

Ancient natural reactors. Some two billion years ago the ore was rich enough in uranium-235 for groundwater to set off chain reactions that flickered on and off for a few hundred thousand years.

Commercial nuclear power plants typically use fuel enriched to roughly what level of uranium-235?

About 4%. Natural uranium holds under 1% of the fissile isotope, so most reactors need only a modest boost, a world away from the 90% or so that a bomb requires.

What was the cheapest and leading method of enriching uranium in the 2020s?

Gas centrifuges. Spinning the gas at enormous speed does the job on roughly a fiftieth of the electricity the old diffusion plants swallowed, which is why every enrichment plant now running uses them.

Which uranium compound is turned into a gas so that enrichment plants can work on it?

Uranium hexafluoride. Known in the trade as 'hex', it is shipped as a white solid and turns to gas at only about 56 degrees C, which is what makes handling uranium as a gas practical.

What is 'yellowcake'?

A uranium oxide concentrate from milled ore. Despite the name, what mills ship today is usually khaki, brown or black; only the concentrates of early mining days were truly yellow.

Which country mined 39% of the world's uranium in 2024?

Kazakhstan. It has led the world since overtaking Canada in 2009, yet it has had no working nuclear power plant of its own since 1999 and only voted to build one in 2024.

As of 2025, which country held more than a quarter of the world's known uranium resources, the largest share?

Australia. Much of it lies in one giant orebody, Olympic Dam, where uranium is a by-product of copper mining, yet Australia has no nuclear power plants and exports every tonne.

High-grade ores in which Canadian basin can average up to 23% uranium oxides?

Athabasca. Its ore runs about a hundred times richer than the world average, and the biggest mines there freeze the soft ground solid and cut the ore out by remote control.

In 2024, which mining method produced more than half of the world's uranium?

In-situ leaching. A solution pumped down wells dissolves the uranium where it lies and is pumped back up, so there is no pit, no waste rock and far less to build, which keeps it cheap.

Where is there a store of uranium far bigger than all known ore reserves?

Dissolved in seawater. The oceans hold billions of tonnes, but at only about three parts per billion, so although Japanese scientists showed in the 1980s that it can be filtered out, it has cost several times as much as mining.

Before radioactivity was discovered, uranium's main use was for what?

Colouring glass. Uranium glass glows bright green under ultraviolet light, and potters used the metal too: Fiesta dinnerware's red glaze contained uranium into the early 1970s.

Much of the uranium for the first atomic bombs came from Shinkolobwe, a mine in which present-day country?

DR Congo. The mine's Belgian boss had quietly shipped more than a thousand tonnes of its rich ore to New York in 1940, so the Manhattan Project found a stockpile already waiting on its doorstep.

Joachimsthal, a Bohemian mining town famous for silver and later for uranium, gave its name to which currency?

The dollar. Silver coins struck there from 1519 were called Joachimsthalers, soon clipped to thalers and then, by way of Dutch and Low German, to dollars.

The discovery of which element in uranium ore made uranium itself a mere by-product?

Radium. Miners went after it for luminous watch and aircraft dials, and until the Second World War the uranium that came out of the ground with it was treated as little more than waste.

Which radioactive gas, produced as uranium in rock and soil decays, can seep into the basements of homes?

Radon. It has no colour or smell, and breathing it in at home over many years makes it the second biggest cause of lung cancer after smoking.

What is the main military use of depleted uranium?

Armour-piercing shells. The metal is so dense that a slim dart of it punches through a tank's armour, and it ignites on impact, burning its way in.

What is the main health risk from depleted uranium?

Chemical poisoning. Depleted uranium is only weakly radioactive, so the real worry is its dust acting like any other toxic heavy metal once swallowed or breathed in, and it is hardest on the kidneys.

As of 2025, which country got about 70% of its electricity from uranium-fuelled reactors?

France. With little coal, oil or gas of its own, it bet on reactors after the 1973 oil shock for the sake of energy security, and went on to sell surplus power to its neighbours.

Uranium absorbed by the body lodges longest in which tissue, thanks to its affinity for phosphates?

Bone. About two-thirds of the uranium in a human body sits there, locked into the mineral, though the organ it harms first is the kidney.

Which Native American nation's uranium miners, many later struck by lung cancer, helped prompt a 1990 US compensation law?

Navajo. They dug uranium for Cold War weapons without protective equipment or any warning of the danger, and more than 500 abandoned mines on their land still await cleanup.

Where are uranium atoms forged?

Exploding and merging stars. Only such blasts cram neutrons onto nuclei fast enough to build atoms this heavy, so every gram of Earth's uranium is older than the planet itself.

Radioactive decay of uranium, thorium and potassium-40 deep inside Earth is thought to drive what?

Mantle convection and plate tectonics. That slow decay supplies about half of the planet's internal heat, so in a sense drifting continents, earthquakes and volcanoes run partly on nuclear power.

Uranium can be transmuted in a reactor into which fissile element?

Plutonium. The surprise is which uranium does it: the common isotope, uranium-238, no use as fuel by itself, soaks up a stray neutron in the reactor and ends up as fissile plutonium-239.

Uranium sounds exotic, yet it is about as common in Earth's crust as which everyday metal?

Tin. At a few parts per million uranium is hardly rare, some forty times more plentiful than silver; what is scarce is ore rich enough to be worth digging up.

Canada's CANDU reactors can burn natural, unenriched uranium because they are moderated by what?

Heavy water. It slows neutrons without swallowing as many as ordinary water does, so in effect Canada chose to enrich the water instead of the fuel; the D in CANDU stands for deuterium.

Early Boeing 747s carried hundreds of kilograms of depleted uranium in their wings and tails as what?

Counterweights. Where the most mass has to fit into the least space, little beats one of the densest metals going, so it balanced the control surfaces of early jumbo jets and has ballasted yacht keels too.

Bacteria that encrust themselves in uranium crystals could help do what?

Clean up polluted water. Citrobacter is the microbe that grows the crystal crust, and another, Geobacter, has been put to work stripping uranium from a contaminated aquifer in Colorado.