The Most Dangerous Rock in the World

In 1789, German apothecary Martin Klaproth extracted a metal from pitchblende rocks from the Jáchymov (Joachimsthal) mines in northern Czech Republic, discovering the element uranium.

Pitchblende—the “most dangerous rock in the world”—journeyed from obscure mineral used for coloring ceramics to the material that enabled both peaceful nuclear energy and devastating weapons, fundamentally reshaping human civilization and geopolitics.

In 1852, George Stokes demonstrated that uranium-colored glass fluoresces under ultraviolet light, revealing an intriguing optical property that would later inspire radioactivity research.

In the late 1800s, physicist Henri Becquerel hypothesized that fluorescent uranium metal might generate X-rays when exposed to ultraviolet light, designing an elegant experiment to test this idea.

In one of science’s luckiest moments, cloudy Paris weather caused Henri Becquerel to store his uranium experiment in a drawer for a week, leading to radioactivity’s accidental discovery when he developed the plate “just for fun.”

Becquerel’s discovery posed a profound mystery that attracted the world’s best scientists including Marie Curie, Pierre Curie, and Ernest Rutherford: uranium continuously emits radiation without apparent energy input.

The spontaneous radiation mystery attracted some of the best scientists in the world, including Marie Skłodowska Curie, Pierre Curie, and Ernest Rutherford, who collaborated and competed to understand radioactivity’s nature.

The Curies and Rutherford discovered something remarkable: uranium was transmuting—turning into other elements while releasing huge amounts of energy in the process.

Radioactivity research revealed that atoms—contrary to their etymological meaning “indivisible”—contain complex internal structure with divisible nuclei composed of protons and neutrons surrounded by electron clouds.

The discovery that atoms transmute contradicted decades of science showing atoms were unchanging building blocks of the universe—the word “atom” literally and incorrectly means “indivisible.”

On the night Marie Curie received her PhD in summer 1903, Pierre brought out a party trick for gathered scientists—a test tube coated in zinc sulfide and full of radium gas that glowed eerily in the Paris night.

In summer 1903, when Rutherford visited the Curies in Paris to celebrate Marie receiving her PhD, he noticed Pierre’s hands were covered in radiation burns from months of laboratory work—an early sign of radioactivity’s power and danger.

Early radioactivity researchers unknowingly exposed themselves to dangerous radiation levels, experiencing burns, cancer, and premature death before understanding ionizing radiation’s biological hazards—Marie Curie eventually died from radiation-induced aplastic anemia.

Rutherford’s colleagues showed that instead of waiting for spontaneous nuclear reactions, scientists could induce these reactions by bombarding atoms with high-speed protons—lithium atoms split into two alpha particles, releasing huge energy.

Lord Rutherford, despite pioneering nuclear physics, declared in a public speech that anyone seeking power from atomic transformation was “talking moonshine”—dismissing nuclear energy as fundamentally impractical despite growing excitement.

Szilard realized that neutrons—recently discovered particles with no electrical charge—would make far superior nuclear projectiles than protons, eliminating the massive inefficiency Rutherford identified.

While crossing a London street in 1933, Hungarian refugee physicist Leo Szilard had a revolutionary insight: what if nuclear reactions could be self-sustaining, with neutrons from the reaction itself triggering subsequent reactions?

In Nobel Prize-winning work, Enrico Fermi took up Szilard’s chain reaction question and over several years systematically bombarded every element on the periodic table with neutrons to find candidates for self-sustaining reactions.

When Fermi bombarded uranium—the last element on the periodic table at the time—he encountered completely anomalous results: no chemical evidence uranium was decaying into neighboring elements, combined with a wide range of radioactive decay half-lives.

Unable to find uranium’s decay products among neighboring elements, Fermi made a controversial hypothesis: uranium was transmuting into heavier, yet-to-be-discovered elements beyond the periodic table’s end.

In 1938, German nuclear chemist Otto Hahn observed that his neutron-bombarded uranium samples were turning into barium—an alarming result he ran repeatedly, looking for mistakes but finding none, before alerting collaborator Lise Meitner.

When Hahn’s letter arrived in December 1938, Lise Meitner desperately needed distraction—as an Austrian of Jewish descent, she’d been forced to flee when Hitler annexed Austria, with her sister and brother-in-law sent to concentration camps.

On Christmas Eve morning 1938, Lise Meitner insisted her nephew Otto Frisch “get to work” on Hahn’s barium puzzle, setting out into Swedish snow—Frisch on skis, Meitner walking briskly—to discuss how uranium could possibly split.

Meitner and Frisch discussed the most complete nuclear mathematical model at the time—the liquid drop model—which treated the nucleus as a droplet held together by surface tension while fighting internal electrostatic repulsion.

When physicists compare an atom’s measured mass to its constituent particles’ combined mass, the numbers never match—atoms always have missing mass, explained by Einstein’s mass-energy equivalence E=mc².

When plotting binding energy per nucleon against atomic mass, an interesting curve emerges: elements toward the periodic table’s center (like iron) have the most strongly bound nuclei, while lighter and heavier elements have less tightly bound nuclei.

Sitting on a log in Swedish snow, Lise Meitner calculated from her memorized binding energy curve that uranium splitting into barium would release approximately 200 mega-electron volts per atom—proving fission was energetically possible.

Meitner and Frisch realized the nucleus could oscillate like a water drop—the incoming neutron’s energy doesn’t need to overcome full binding energy, only enough to make the nucleus “wobbly” and deform past a critical point.

Within weeks of the Christmas Eve calculation, Otto Frisch experimentally validated the fission results, confirming that uranium bombardment actually produced the predicted energy release and fragment patterns.

Otto Frisch gave the nuclear splitting phenomenon its name—“fission”—borrowing biological terminology for cell division to describe uranium nuclei splitting in two.

Word of fission discovery spread rapidly across the globe—when news reached Niels Bohr (Frisch’s mentor), he said “what fools we have been”; graduate student Luis Alvarez ran out mid-haircut in California to alert advisor Robert Oppenheimer.

Within months of fission’s discovery, another member of the Curie family experimentally showed that uranium fission releases two or more neutrons per reaction—making Szilard’s vision of nuclear chain reactions a real possibility.

The combination of fission releasing 200 MeV per atom and producing 2+ neutrons meant Szilard’s 1933 chain reaction vision became reality: one fission triggers two, two trigger four, four trigger eight—exponential cascade.

Calculating from 200 MeV per atom, one kilogram of uranium-235 undergoing complete fission releases approximately 81 terajoules of energy—20 million times the energy from one kilogram of TNT.

As World War II loomed, the catastrophic military potential of nuclear chain reactions was not lost on governments—the United States, Germany, and Japan all began research programs aimed at building atomic bombs. The race had begun.