Orignal Author
Yi-Heng Sung
English Translator
Yi-Heng Sung
Copyright© LIS情境科學教材
Discrimination is everywhere in this world, and gender discrimination is one of the oldest forms. “All men are created equal”—the opening line of the U.S. Declaration of Independence in the 18th century—was meant to symbolize the ideals of freedom and equality. But how about women? Today, we might interpret “men” to mean “people,” but it’s clear that, at the time, women were not even part of the conversation. Their rights were simply not on the table. It wasn’t until the 20th century that the United Nations’ Universal Declaration of Human Rights used the term human, symbolizing a step toward gender equality. Even in the first morden democroic Britain, the 19th-century push for universal suffrage—regardless of class or race—still applied only to men.
This inequality extended to science as well. Scientific research had long been dominated by men, and even today, in the 21st century, we still hear prejudiced claims that women are less capable in logic and mathematics. Yet, at the end of the 19th century—when gender discrimination was the norm—a fearless scientist emerged. Through her brilliance, she proved that people should not be defined or limited by their gender.
At the same time, the focus of physics was shifting—from the macroscopic to the microscopic perspective, from what we could see to what we couldn’t. In 1895, German physicist Wilhelm Röntgen, while experimenting with cathode rays in vacuum tubes, noticed something unusual: when the tube was powered, a screen coated with barium platinocyanide began to glow with phosphorescence. Even more astonishing, when he placed his hand between the screen and the tube, he saw the image of his own bones projected onto the screen. He named this mysterious radiation “X-rays”—a name we still use today.
The following year, French scientist Henri Becquerel noticed that uranium salts also emitted rays that caused phosphorescence and could pass through materials. However, unlike X-rays, which require an external energy source like cathode rays to activate them, the radiation from uranium salts was spontaneous. Other phosphorescent substances—such as zinc sulfide—needed to be exposed to sunlight before glowing, and even Röntgen’s X-rays needed cathode rays. But uranium salts glowed all on their own.
Becquerel also observed two notable properties of this radiation: it could darken photographic plates, and it could make the surrounding air electrically conductive. He discovered that the radiation from uranium salts caused the leaves of a gold-leaf electroscope—an instrument that detects electric charge—to collapse. This meant that the radiation was somehow ionizing the air, allowing electric charge to leak away. In other words, uranium rays increased the conductivity of air.
Image│The world’s first X-ray image. Röntgen discovered that X-rays could pass through soft tissue, revealing bones.
Image│Gold-leaf electroscope
Just like a falling star marks the rise of another, the death of Michael Faraday—the legend of electromagnetism—in London in 1867 coincided with the birth of Marie Skłodowska-Curie (1867–1934), one of the most renowned female scientists in history, born in the eastern city of Warsaw.
Image│Maria Skłodowska-Curie
Marie Curie was born into a well-educated family. Her mother was the principal of the best girls’ school in the area, and her father was a math and physics teacher at a local secondary school. Beyond their strong academic values, her family did not believe in the idea that “女子無財便是德 (a woman’s virtue lies in her lack of talent, means women should not be educated).” On the contrary, they strongly supported their daughters in pursuing academic excellence. After graduating high school with top marks, Maria, like her older sister Bronya, was determined to study abroad. However, their family couldn’t afford the steep tuition and living expenses for both of them, so the sisters made a pact to help each other—taking turns to work and support the other’s dream of studying in Paris.
According to their plan, Marie would work first to earn money for Bronya’s education. After Bronya completed her studies, she would return the favor. So after high school, Marie spent eight years working as a private tutor, attending lectures when she could, and saving every penny to support both her own and her sister’s dreams. During those eight years, she taught children from different households by day and continued studying by night. Through this cycle of learning and working, Marie decided to study physics and mathematics in university. In 1891, after Bronya successfully earned her medical degree in Paris, Marie was finally able to fulfill her long-held dream of studying in the City of Light.
Image│The Skłodowska family; Marie is the first from the left
Image│Marie (left) and her sister Bronya (right)
In just three years, Marie Curie earned degrees in both physics and mathematics. Her outstanding performance caught the attention of Professor Gabriel Lippmann, who helped her obtain a research project funded by Société d'encouragement pour l'industrie nationale. This opportunity marked the beginning of Maria's long but fulfilling research journey in Paris—and the start of her love story.
The research project involved studying magnetic properties of different metal alloys, which required a larger laboratory to house her instruments. While she was struggling to find a suitable lab, a friend introduced her to a local young scientist, Pierre Curie, who might be able to help. Love struck like a tornado—their mutual passion for science drew Marie and Pierre closer, and before long, they developed a deep affection for each other. Pierre, eager not to miss this rare connection, quickly proposed. But Marie’s heart still longed for her homeland Poland. She planned to return and contribute to her country’s scientific development after completing her work in Paris.
Marie thought she could continue her scientific career at a university in Poland, but due to the severe gender inequality of the time, she was rejected solely because she was a woman. In the end, unable to resist the pull of destiny, Marie returned to France and married Pierre Curie in 1895. From then on, she became the Madame Curie we all know today.
Image│Gabriel Lippmann
Image│Pierre Curie
Image│The Curies working together in their lab
Just a year after their marriage, in 1896, Henri Becquerel—another French scientist—discovered that uranium salts emitted mysterious rays similar to X-rays. Yet, at the time, this discovery barely made a splash. Only a few days after observing the phenomenon, Becquerel presented his findings at a scientific meeting, but the audience merely listened quietly, showing little interest. Although he had identified unique features of the radiation (such as its ability to increase air conductivity), the discovery didn't gain traction, and Becquerel soon withdrew from further research in the area.
One year later, as Marie Curie was preparing to pursue her doctoral degree, she began searching for a research topic. That’s when she remembered the mysterious radiation from uranium—a discovery largely forgotten by the scientific community. She believed these rays were fundamentally different from any known type of radiation and thus were worth investigating. With that, Marie chose uranium radiation as the focus of her doctoral research—and the legend began.
Based on Becquerel’s research, Marie Curie already knew that uranium and its compounds emitted a special kind of radiation. However, when she wanted to compare the strength of the radiation emitted by uranium and its compounds, she found that no tools were available to help her. Marie realized that the tools of the time could only detect the presence of radiation, not measure its intensity. Since this type of radiation is invisible to the naked eye, Becquerel had observed its existence using photographic plates and a gold-leaf electroscope—radiation would darken the photographic plates and cause the electroscope’s leaves to collapse. But neither of these methods was precise enough to quantify the radiation's strength. Therefore, Marie needed a more accurate tool to measure the intensity of radiation from uranium salts.
Marie recalled from Becquerel’s research that this type of radiation could not only darken photographic plates but also increase the conductivity of the surrounding air. This meant that the stronger the radiation, the greater the conductivity of air molecules. She thus hypothesized that by measuring the air’s conductivity, she could infer the intensity of the radiation. Marie reasoned that since radiation increased the air’s ability to conduct electricity, the stronger the radiation, the more conductive the air would become—making air conductivity a proxy for radiation intensity.
Marie had figured out that air conductivity could indicate radiation strength, therefore she wanted to design experiments to test her hypothesis. However, she discovered that there were no instruments capable of accurately quantifying small changes in air conductivity. Air is naturally a very poor conductor, and even when radiation increases its conductivity, the amount of current it can carry remains extremely small. At the time, gold-leaf electroscopes could detect the presence of electric charge, but they weren’t precise enough to measure such minuscule electric currents.
There’s a sexist old saying that “behind every successful man, there’s a great woman,” but the reverse is just as true: behind every successful woman, there’s often a great man. Marie thought of her husband, Pierre Curie, who had worked with his brother a decade earlier to develop a piezoelectric device. This instrument could generate a fixed, tiny electric current by compressing or stretching a crystal (such as quartz). That meant she could use it to generate a consistent electrical charge for every experiment.
Marie then had another realization: since radioactive substances made air slightly conductive, it would take a long time for electricity to discharge through the air. By calculating how long it took for electricity to be conducted through the air, she could determine how much the radioactive substance had increased air conductivity, and thus measure the substance's radiation intensity.
So Marie concluded that since Pierre’s piezoelectric device could produce a fixed, weak current for each experiment, and since radioactive materials took a long time to conduct electricity through air, she could calculate the radiation intensity by measuring how long it took the electric charge to discharge. By generating a fixed charge with Pierre’s device and letting different radioactive substances conduct the electricity through air, she could simply measure how long it took for the charge to discharge—and from that, determine the intensity of the radiation.
Image│Pierre Curie and his brother’s invention, the piezoelectric electrometer.
If Marie's hypothesis was correct—namely, that the conductivity of air increases in the presence of radiation—then different radioactive substances would take varying amounts of time to discharge the current produced by a piezoelectric device. From this, the intensity of the radiation could be inferred.
Image│A schematic of the apparatus used by Marie Curie in 1898: The substance to be measured is placed on the metal plate labeled B. The radiation increases the conductivity of the air, generating a faint electric current. Q represents the quartz used in the piezoelectric electrometer invented by Pierre Curie.
First, Marie connected a piezoelectric crystal with a device designed to hold radioactive substances (Sample Ionization), both of which were linked to a quadrant electrometer. She placed a weight on the piezoelectric crystal, which caused it to produce a constant electric charge, leading to a deflection of the electrometer's needle (represented by a light spot via a mirror).
Next, she inserted the radioactive substance between two metal plates inside the ionization chamber. This setup caused the air between the plates to become conductive, allowing the electric charge from the piezoelectric crystal to gradually leak away. As the charge dissipated, the deflection of the electrometer's needle gradually returned to its original position.
Finally, using a stopwatch, Marie recorded the time it took for different radioactive substances to discharge all the electricity—i.e., the time it took for the needle to return to zero. She observed that pure uranium metal discharged the electricity in about one-third the time compared to uranium sulfide. Her calculations confirmed that the mass of uranium in both substances also differed by a factor of three. These findings supported her hypothesis and demonstrated that radiation intensity could be measured using this method and apparatus.
In 1898, Marie Curie was the first to describe the property of emitting special rays as radioactivity, and the rays themselves are now known as radiation. From Becquerel’s discovery of a mysterious X-ray-like emission in 1896 to the Curies’ contributions, a series of major breakthroughs occurred in less than a decade. With the help of her custom-designed instrument, Marie continued her investigation. She discovered that the known element thorium (Th) also exhibited radioactivity. Furthermore, in 1898, she found that natural uranium ore emitted much stronger radiation than the amount of uranium present should have accounted for.
Using qualitative analysis, she separated various compounds from the ore and measured their radiation intensity using her detection device. Any substance still exhibiting radiation was subjected to further analysis. Through this process, Marie discovered two new radioactive elements—polonium (Po) and radium (Ra)—both significantly more radioactive than uranium.
Marie’s discoveries captured the attention of the scientific community. In 1903, the Royal Society of London invited the Curies to present their work on radiation. Unfortunately, due to rampant gender discrimination, only Pierre was allowed to speak, while Marie was barred from the podium because of her gender.
However, her perseverance paid off. Recognizing the profound importance of radiation and radioactive elements in science, the Nobel Committee sought to award the 1903 Nobel Prize in Physics to those who had contributed to its discovery. Initially, only Becquerel and Pierre Curie were selected. Marie was overlooked despite her substantial contributions. Thanks to the efforts of a pro-women scientist who advocated for her, Marie finally received the recognition she deserved. That year, she shared the Nobel Prize in Physics with Becquerel and Pierre Curie, becoming the first woman to win a Nobel Prize—a landmark moment for women in science. Marie did not rest on her laurels. She spent years successfully isolating radium from ore and was awarded the 1911 Nobel Prize in Chemistry, becoming the first person ever to win two Nobel Prizes.
Her research profoundly shaped the scientific world. The discovery of radiation laid the foundation for modern physics. The New Zealand physicist Ernest Rutherford, using a radiation detection device similar to Marie's, found that uranium rays had two different penetration abilities after passing through aluminum foil. He named the weaker rays alpha (α) rays and the stronger ones beta (β) rays.
This discovery of α rays led to the famous Rutherford gold foil experiment in 1909. Under Rutherford’s guidance, his students bombarded gold foil with α particles and found that while most passed straight through, a few were deflected. This suggested that atomic mass was concentrated in a small nucleus, leading to the Rutherford atomic model and a new era in physics.
In 1917, Rutherford bombarded nitrogen atoms with α rays, knocking out a proton and transforming it into an oxygen atom—the first artificial nuclear reaction in history. This experiment paved the way for nuclear energy and the development of the atomic bomb.
While β rays may not have as dramatic a backstory, they are widely used in daily life. For instance, the glow-in-the-dark watches use tritium (T), which emits β rays. In the paper industry, β rays are used to control the thickness of paper: by measuring how much β radiation is absorbed by the paper, manufacturers can determine if the paper is too thick or thin.
Image│Ernest Rutherford, the New Zealand physicist
Marie Curie was a pioneer of gender equality. Despite repeated rejection due to her gender, she persisted with quiet strength. Early in her career, universities in Poland refused to hire her simply because she was a woman. But after receiving her first Nobel Prize, no one could ignore her scientific achievements. In 1906, she became the first female professor at the University of Paris.
Her courage and determination have inspired generations of women for nearly a century. Her daughter, Irène Joliot-Curie, followed in her footsteps and, alongside her husband, won the Nobel Prize in Chemistry in 1935. Marie’s granddaughter, Hélène Langevin-Joliot, is a nuclear physicist who has taught at the University of Paris, her grandmother’s alma mater.
Marie Curie’s story continues to inspire even nearly 90 years after her passing. In a 2009 UK survey, she remained the most inspiring female scientist in the public’s eyes.
Image│Irène Joliot-Curie, daughter of Marie Curie
Image│Hélène Langevin-Joliot, granddaughter of Marie Curie
Though the world remembers her as Madame Curie, Marie Curie was never anyone’s shadow. She carved her path in a male-dominated field, overturned prejudice through talent and grit, and etched her name into the annals of scientific history—Marie Curie.
Image│ Marie Curie among male scientists (1911 Solvay Conference: front row, second from right: Marie Curie; back row, fourth from right: Rutherford; back row, second from right: Einstein)
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