What Becquerel was seeing, of course, was evidence of radioactivity—the tiny particles that uranium is always casting away from itself.
He could not have known it at the time, but this instability that characterizes uranium was due to its heaviness. With ninety-two protons jammed together in its nucleus, uranium is the fattest1 atom that occurs in nature and is therefore in a constant state of disintegration.
A useful metaphor for radioactivity might be found in architecture, and a good place to look is at a curious building on West Jackson Boulevard in downtown Chicago. The Monadnock Building is sixteen stories tall, and when completed in 1891, it was an object of popular marvel because it was the tallest building in the world. Steel was still expensive, and architects had not yet learned how to build with the kind of internal frames that could lift an edifice a hundred stories or more. All the weight of an edifice, therefore, had to rest on its walls, as it had since before the time of the Bible. The Monadnock was stone and mortar, and sixteen stories was the breaking point with those materials. Any higher and the whole thing would fall into a pile of rubble, or require walls so big and windows so small that the rooms would have resembled dungeon cells. Even so, the walls of the Monadnock are grotesquely thick, bulging six feet outward at the ground level. The building is so obese with masonry that it sank nearly two feet into Chicago’s lakefront soil after it opened. It is still the tallest building in the world without a steel frame, and it represents a monument of sorts: the very brink of physical possibility, like the notion of absolute zero, at 459 degrees below Fahrenheit, beyond which molecules stop moving altogether and cold can get no colder.
There is a similar invisible limitation inside atoms, and uranium is the groaning stone skyscraper among them, pushing the limits of what the universe can tolerate and tossing away its bricks in order to forestall a total collapse. This is radioactivity.
Becquerel’s discovery attracted the attention of another Parisian—a thirty-one-year-old graduate student named Marie Sklodowska who had recently emigrated from Poland and married fellow physicist Pierre Curie. While working on her doctoral thesis, she suspected there must be traces of an unknown element, spraying even more radioactivity, hiding deep within uranium. Without having seen it, and acting only on a hunch, she named it radium.
Pierre and Marie Curie wrote to the Austrian Academy of Sciences to ask about the slag heaps at St. Joachimsthal. At the turn of the twentieth century, Martin Klaproth’s “strange new metal” was still regarded as a worthless tagalong of silver, good only for making colorful stains for ceramics. The leftover piles of “bad-luck rock” had simply been dumped in the pine forest.
One ton was released to the Curies free of charge, and the remaining stocks were priced at a deep discount. In the summer of 1898, a horse-drawn wagon delivered several canvas bags full of sandy Bohemian pitchblende. Mingled inside were stray pine needles from the trees. Pierre had secured the use of a shed that had previously been used to dissect human corpses. The only furniture inside was a cooking kiln and a series of pine tables where Marie piled her pitchblende.
When dissolved in solution, boiled, and then cooled, the pitchblende formed crystals in much the same way that cooling saltwater leaves flakes of salt on the edge of a glass. “Sometimes I had to spend a whole day stirring a boiling mass with a heavy iron rod nearly as big as myself,” she recalled later. Marie examined the crystals with an electrometer, setting aside the specks with the most powerful radioactive signatures.
She was eventually able to isolate a tenth of a gram of radium chloride and prove it was a new element that deserved its own spot in the periodic table. Marie and Pierre were jointly awarded the 1903 Nobel Prize in physics, shared with Becquerel, for their discovery of radiation phenomena. The French newspapers fell in love with the Curies and their cadaver shed. Pierre made a show of exposing his arm to radium to create a burn, which healed after two months, to demonstrate what he called radium’s abilities to cure cancer.
Doctors confirmed that he was right. Concentrated doses of radium could indeed shrink and even eliminate tumors. The radiation seemed to kill younger cells—in particular, the cancerous ones—while leaving healthily matured cells untouched. “It was just as miraculous as if we had put our hands over the part and said, ‘Be well,’ ” reported one Johns Hopkins physician after giving radium treatments to a man with a bulbous tumor on his head. The tumor had vanished after radium treatments. Cosmopolitan magazine trumpeted radium’s virtues in an article that called it “life, energy, immortal warmth” and “dust from the master’s workshop.” A San Francisco company added trace amounts to chocolate bars. Glow-in-the-dark crucifixes were coated with radium paint. A potion called Radium Eclipse Sprayer claimed to work as both a bug killer and a furniture polish.
The St. Joachimsthal mine directors, who had been happy to give away their trash for free when the Curies had asked for it, now set to exploiting the “bad-luck rock” as the centerpiece of a spa business. They built a two-mile pipeline to carry hot water to the center of the medieval town, which was close enough to Vienna and Prague to attract some of those cities’ smart sets. Coach tours were commissioned, and a rail spur was added. St. Joachimsthal was soon welcoming twenty-five hundred visitors a year. One of them was a blue-eyed American private school student named J. Robert Oppenheimer, who would later say his interest in science began when his uncle gifted him a collection of colorful stones picked from the St. Joachimsthal mines.
New brick town houses sprang up in place of the cottages where miners had died of the mysterious wasting disease. The Radium Palace Hotel, with a grand marble staircase and fountain garden in the front, was built on a slope overlooking the valley. A local brewery turned out bottles of Radium Beer. Marie Curie herself was invited to make a sentimental pilgrimage to the “birthplace” of the mineral that had made her and her husband famous.
But, in fact, both Marie and Pierre were ill with radiation sickness, unknown at the time. When the physicist Ernest Rutherford paid the couple a visit in Paris in 1903, he noticed that Pierre’s fingers were red and inflamed, shaking so badly he could barely hold a tube of radium salts that he was showing to his guests. Pierre was too sick to present his Nobel lecture and had to postpone it for two years. When he finally stood in Stockholm to receive the award, his tone was hesitant.
“Is it right to probe so deeply into nature’s secrets?” he wondered. “The question must here be raised whether it will benefit mankind, or whether the knowledge will be harmful. Radium could be very dangerous in criminal hands.”
He finished his address on a hopeful note, invoking the name of the Swedish chemist Alfred Nobel, who had become rich from inventing dynamite and was savaged as a “merchant of death” by the newspapers, but who had also become a pacifist and endowed the famous prizes that celebrated advances in science, art, and peace.
“The example of the discoveries of Nobel is characteristic, as powerful explosives have enabled men to do wonderful work,” concluded Pierre Curie. “They are also a terrible means of destruction in the hands of great criminals who are leading the people toward war. I am one of those who believe with Nobel that mankind would derive more harm than good from these new discoveries.” Scientific curiosity was moving forward, a relentless force.
This strange energy inside uranium, this radioactivity, was causing scientists to reexamine some long-standing assumptions about the cosmos. The basic understanding of the atom, for example, was about to take a radical shift.
An atom is approximately one hundred millionth of an inch across, tiny enough to be everywhere and invisible at the same time. The existence of these universal building blocks was first theorized in the fourth century B.C. by a wealthy Greek dilettante named Democritus, who was amplifying an earlier theory from a philosopher named Leucippus. Both men were in rebellion against the concept of monism, which holds that all substance, including empty space, is a single unified object bound together with invisible connections. Democritu
s proposed the concept of a pixilated world made up of tiny basic balls of matter that were impossible to split. He coined the word atom, which literally means “indivisible,” and described atoms as being constantly vibrating and in motion, banging against one another and binding to one another in distinct patterns to form the minerals and vegetables of the world: gold, sand, trees, the ocean, even man himself. One of his followers compared the movement of atoms to the lazy meanderings of dust particles inside a sunbeam.
The exact nature of these atoms was left murky, but Democritus speculated that they had the reduced characteristics of their grander forms: Atoms of water were slippery, atoms of sand were sharp and jagged, atoms of fire were hot and red, and so on. He even believed the human soul was made of atoms, which disperse to the winds upon death, forever obliterating that person. Democritus was not a believer in immortality.
The notion of a miniature world wriggling out of the sight of mankind was disturbing to more classic theorists, including Plato, who preferred to think of the inner firmament of the world as a divination of the gods, and not anything that could be expressed as tiny dots. The atomic proposition also seemed to wreck the famous paradox of Zeno’s arrow, which must travel half the distance to its target, but before that, half of that half, and before that, half of the half of the half, and so on into infinity, meaning that the arrow ought to be in flight forever, but it clearly was not. Space and matter were not, therefore, infinitely divisible. They were hardened on some level, just as Democritus was suggesting. Plato was supposed to have told his friends he wished all sixty books by Democritus could be burned.
The wish might as well have come true, for none of Democritus’s writings survive today in their original form. All we know of him is what his contemporaries said, which was often disparaging. Portions of Democritus’s atomic theory, however, proved remarkably durable and stood without challenge for more than twenty centuries. Galileo and Sir Isaac Newton were believers in a universe made of circular points invisible to the eye, and Newton spent the latter part of his career in a fruitless quest to turn one element into another through alchemy. He never renounced his belief in the indivisibility of atoms, however, writing in his book Opticks: “It seems probable to me that God, in the beginning, form’d matter in solid, massy impenetrable particles . . . even so hard as never to wear or break into pieces, no ordinary power being able to divide what God Himself made one. . . .” The British chemist John Dalton, after conducting a series of experiments with gases in the eighteenth century, concluded not only that Newton was correct about a hard-balled universe but that atoms of a particular element were all exactly the same and that they were neither created nor destroyed.
The rapid discoveries about uranium at the beginning of the twentieth century, as well as the enthusiastic fictions of H. G. Wells, were challenging this ancient scientific orthodoxy. If uranium was tossing off particles that could be measured with an electrometer, then clearly a portion of matter existed that was even smaller than the atom itself. But what was it? And why was the uranium atom so eager to fling these specks?
The man who brought the world to the edge of these questions, and who did more than any one person to vivisect the atom, was Ernest Rutherford. The son of a poor New Zealand flax miller, Rutherford, at age twenty-four, won a scholarship to study physics at Cambridge and quickly amused his colleagues with his bluff antipodean manners. One colleague likened him to the keeper of a small general store in sheep country: “He sputtered a little as he talked, from time to time holding a match to a pipe which produced smoke and ash like a volcano.” But the sodbuster exterior concealed a visionary mind, capable of drawing sublime inferences in the laboratory.
In 1906, Rutherford took a second look at Becquerel’s rays, having previously categorized them into types. There was first the alpha ray, which could be stopped by skin or a piece of paper. There was then the beta ray—a free electron—which was negatively charged and could be blocked with an aluminum plate or a few sheets of paper. In order to understand the way the rays moved, Rutherford asked a graduate student to build a device that scattered particles from some of Marie Curie’s radium through a narrow tube, after which they hit a screen coated with zinc sulfide. There they made a tiny spark that could be observed through a microscope. Further assistance was given by a student named Hans Geiger, who built a simple device out of a gas-filled tube and a thin metal wire that acted as an electrode. When a particle passed through this chamber, it set off an audible click. This became the prototype for the famous Geiger counter, the universal handheld radiation detector.
Rutherford put some gold foil at an angle to the zinc screen, which was out of the direct path of the radium.
What he witnessed was baffling. The alpha rays should have been passing through the foil. But a tiny percentage of them seemed to be bouncing off the gold foil and onto the zinc screen, in much the same way that a basketball will bank off a backboard and into the hoop.
“We found that many radiated particles are deflected at staggering angles—some recoil back along the same path they had come,” said Rutherford. “And considering the enormous energy of the alpha particles, it is like firing a fifteen-inch shell at a piece of tissue paper and having it flung back at you.”
He concluded that the alpha rays must have been bouncing off the hard core of the nucleus itself. Only one or two particles in a million were recoiling this way, suggesting that the nucleus was quite tiny and that only an extremely lucky shot could strike it—the equivalent of a hole-in-one golf shot. This suggested a much roomier atom than anyone had envisioned: a giant chamber of empty space with a positively charged center. If the atom were the size of a rugby field, its nucleus would be about the size of a strawberry seed.
“I was brought up to look at the atom as a nice hard fellow, red or gray in color, according to taste,” Rutherford recalled later. That idea was now dead forever: There were now known to be interior gears that behaved in odd ways.
Rutherford had helped map the inner space of an atom, but he could not shake the idea that a ghost was hiding somewhere inside the structure. Protons and electrons announced their presence with a telltale electrical signal. But what if a fragment was lurking there that had no electrical aspect whatsoever? Invited to give a lecture to the Royal Society in London in 1920, Rutherford served up the scientific equivalent of a dead fish: an unsupported hunch.
There might be, he suggested, such a thing as an atomic particle “which has zero nuclear charge” and could therefore “move freely through matter.” Such unrestricted movement through inner atomic space would have been out of the question for a proton or an electron, which would be bounced away from any surface because of its charge. But this phantom mote, if it existed, “should enter readily the structure of atoms, and may unite with the nucleus.”
He was proposing a radical concept: that a particle released from one atom might slip past the shield of electrons and penetrate the nucleus of another, as a sperm fertilizes an egg. If this were the case, what would happen to the receiving atom in question? Would it change form? Would it explode?
One of Rutherford’s assistants, a bespectacled twenty-nine-year-old named James Chadwick, resolved to find out if this unassuming particle existed. The riddle had been pushed along with some previous work on the part of Irène Curie, Marie and Pierre’s daughter, who had been conducting experiments on the element beryllium alongside her husband, Frédéric Joliot. They had been firing alpha rays from polonium as “bullets” aimed at a sample of beryllium and witnessed the scattering of protons from the target—at three times the energy of the bombardment. The French couple made a key mistake, however, by concluding that this must be a form of gamma radiation, a type of electromagnetic wave.
Chadwick was known for his English reserve and milquetoast personality (he resembled, as one historian noted, a bit of a neutral particle himself), but he was irritated enough to shout, “I don’t believe it!” when he read the results of the French exper
iment. He seemed to find the miscalculation almost offensive. Chadwick set out to replicate the beryllium experiment, except that he bombarded a host of other elements to show that protons were bumped out of them, too, and at a similarly rapid speed.
His conclusion was the reverse of the Joliot-Curies’: The beryllium was not the source of the energy. Something lying near the heart of the alpha ray had to be causing the transfer of all that energy, and logic pointed to the lumpy ghost that Rutherford had predicted twelve years earlier. It was detectable only by the neighboring particles it caused to recoil. Rutherford himself later put it in vivid terms: It was like “an invisible man passing through Piccadilly Circus—his path can be traced only by the people he has pushed aside.” Chadwick named this zero-charged particle the “neutron” and was consequently awarded the 1935 Nobel Prize in physics.
The basic map of the atom was nearly complete. And a few people around the world were beginning to grasp an ominous possibility.
“We have still far to go before we can pretend to understand the atom and the secret of matter,” said the New York Times in a year-end roundup of scientific discoveries in 1932. “But we have gone far enough to think of an engine which will harness the energy released in atom building.”
On September 11 of the following year, Ernest Rutherford gave the Times of London an interview in which he praised the uncloaking of the neutron as a giant leap forward. But he added that anyone who thought that useful power might be derived from neutron collisions was “talking moonshine.”
A physicist named Leo Szilard happened to read this article while he was sitting in the lobby of a shabby London hotel. He became irritated, thinking Rutherford far too glib and blind to the destructive possibilities that the neutron suggested. Adolf Hitler had been appointed chancellor in Germany nine months before, and his ascendancy portended dark changes across the Continent. The next war, if it involved Germany, would likely turn on advances in technology, just as World War I had midwifed the tank, automatic rifles, and mustard gas. Szilard had been hounded out of his native Hungary by a rising tide of anti-Semitism, and he felt the world was becoming too dangerous to risk ignoring the military use of science.
Tom Zoellner Page 4