How Marie Curie Discovered Radium

How was radium discovered in an unventilated shed?  Why was radioactivity discovered and called radioactivity?  What is, arguably, the most influential Ph.D. dissertation of all time?  Well, it all has to do with a fascinating woman named Marie Sklodowska Curie.

Table of Contents

Marie Curie’s Early Life

How Radium Was Discovered

The Radioactive Study


Marie Curie’s Early Life

Maria Sklodowska was born in Warsaw, Poland in 1867 and was the fifth child of a science and math schoolteacher and a school principle.  However, Maria’s family suffered because they were fiercely patriotic to Poland while it was under the regime of the Russian empire. 

In fact, Maria’s father lost his job because of his politics.  A series of tragedies followed, her father lost their savings in bad investments requiring them to rent to boarders, then her oldest sister died of typhus from a boarder, and then her mother died of tuberculosis!  

When Maria (who was called Manya in Poland) was 17, she and her sister “Bronya” made a pact: Manya would work as a governess and earn enough money for Bronya to get an education in Paris and then Bronya would support Manya in her education (the only education available to women in Poland at the time was in an illegal night school called “The Flying University” which had limited classes and, as it was illegal, proffered no degrees). 

Manya then took a job as a governess, first for a family in Krakow that was, according to Manya, “sunk in the darkest stupidity”.  As Manya felt that she, “shouldn’t like my worst enemy to live in such a hell,[1]” she transferred to work for a family north of Warsaw who, at first, seemed like a much better fit. 

All that changed when the eldest son came home from school and they fell in love and wanted to marry.  His parents loved Manya as a governess but hated her as a future daughter-in-law and forbade the marriage.  After much dithering with her feelings the son heeded his parents wishes. 

Manya complained to her cousin, “let [him] go to the devil![2]”.  She then tried to devote herself to self-study. In October of 1888 she wrote her brother, “I am learning chemistry from a book.  You can imagine how little I get out that, but what can I do, as I have no place to make experiments or do practical work. [3]”(A continuing problem for her).

However, despite her irritation with her lover, she continued to see him and when the parents found out they fired her.  Despondent, Manya went home.  When Bronya wrote her in March of 1890 to come to Paris she hesitated for months in the hopes that the young man would change his mind writing her sister, “I have been stupid, I am stupid and I shall remain stupid all the days of my life[4]”.

Finally, after receiving a nasty break up letter, Manya moved to Paris in fall of 1891 to study science at the Sorbonne.  In France, she renamed herself “Marie”, and lived a monastic existence on little money subsiding on so little food that she often fainted.  Finally, in 1893, a Polish friend, “moved heaven and earth” to get Marie a scholarship. 

Now she had a little money to eat and study and set out to find a place to do original research.  It was for that reason she met a French physicist named Pierre Curie.  They quickly fell in love and Pierre wanted to get married but Marie felt that she had to go back to Poland, saying, “Poles have no right to abandon their country”. 

Pierre wrote Marie, “It would be a beautiful thing, a thing I dare not hope, if we could spend our life near each other, hypnotized in our dreams: your dream for your country; our dream for humanity; our dream for science [but] we are powerless to change the social order… [with science, however, perhaps] we can … accomplish something.

[5]”  Perhaps it was Pierre’s love letters or her home countries refusal to allow her to work at a university even with degrees in Math and Physics but Marie decided to return to Paris, marry Pierre, and attempt to get a Ph.D.  Note that at this time no women anywhere in the world had a Ph.D. in science! 

First, however, Marie earned money teaching science to young women and working with industry on the magnetism of metals (she wanted to earn money to pay back the scholarship).  To all of this was the joyous news that they were expecting a baby.  Marie gave birth to Irene Curie in September of 1897. 

Marie recalled: “It became a serious problem how to take care of our little Irene and of our home without giving up my scientific work.  Such a renunciation would have been very painful to me, and my husband would not even think of it.”  Luckily, they had just enough money to hire a servant and Pierre’s newly widowed father moved in to help with childcare. 

How Radium Was Discovered

Marie Curie then looked for an idea for her doctorate.  Luckily, in January of the previous year, 1896, a wealthy French physicist named Henri Becquerel had learned that x-rays were created when an invisible “cathode ray” hit glass and made it fluoresce. 

Now Becquerel had gotten his doctorate on fluorescence and phosphorescence (fluorescents glow only when hit with visible or UV light and phosphors glow after the light is removed).  Becquerel wondered fluorescent or phosphorescent materials would produce x-rays.  By February 24th, Becquerel happily reported that phosphorescent uranium salts would produce invisible rays that would go through the paper and could be seen in the film[6]

Just two days later, he created some uranium salt but the day was cloudy so Becquerel left the sample in a dark desk drawer.  The next two days were also cloudy and, frustrated, Becquerel decided to develop the film as a baseline for his experiments, “expecting to find the images very weak.[7]” 

Instead, to his complete surprise, “the silhouettes appeared with great intensity[8].”  He immediately decided that the uranium was making invisible waves in the darkness on its own without any input!  The uranium was naturally decaying and producing radiation.  The very next day, March 2nd, 1896, Becquerel published “On the Invisible Rays Emitted by Phosphorescent Bodies” where he quite rightly said that his discovery,“seems to me quite important and beyond the phenomena which one could expect to observe.

[9]”Becquerel also found that the uranium didn’t even need to be florescent and called these new rays uranium rays.  Becquerel was excited, but most of the world was not.  Radiation from uranium goes through bones just as well as flesh so it was useless for medical x-rays. 

However, Marie Sklodowska Curie was interested.  She also recalled that 17 years earlier her husband and his brother had discovered piezoelectricity: physics property where changing the pressure creates electricity in certain crystals and that applying electricity will cause those crystals to deform. 

The brothers then created a device to detect very low currents by measuring the pressure on these crystals that was almost as sensitive as modern electronic devices!  Now Becquerel had found that uranium “rays” could make gasses conduct electricity so Marie used her husband’s device to make a more accurate and sensitive measure of radioactivity. 

Marie recalled that, “Instead of making these bodies act upon photographic plates, I preferred to determine the intensity of their radiation by measuring the conductivity of the air exposed to the action of the rays[10]”. 

In this manner Currie determined that the amount of radiation produced was dependent on the amount of uranium present and nothing else (like temperature or whether the uranium was pulverized or wet or whatever).  Becquerel came to the same conclusion, but with less formal proof. 

The Radioactive Study

But then Marie Curie took it to another level.  She wondered if maybe the uranium was emitting rays because of something that was happening with the atoms.  She also thought that there must be other materials that make these rays, stating years later that, “it was scarcely probably that radioactivity, considered as an atomic property, should belong to a certain kind of matter to the exclusion of all other.[11]

Marie Curie then collected every known substance that she could and exhaustively studied them in the electroscope.  By April of 1898, Curie had found that Thalium was about as radioactive as Uranium.  As there were two substances that exhibited this phenomenon, it seemed inappropriate to call them uranium rays and Currie decided to name this radiation radio-active (as in radiation active) and the name stuck, although without the dash.

While she was researching every material she could get her hands on, Marie Curie studied many minerals and ores, which are composed of many elements.  She was not surprised to find that ores with uranium and thallium were radioactive.  However, she was astonished to find that some uranium ores were significantly more radioactive then pure uranium! 

Marie Curie: “I then made the hypothesis that the ores… contain in a small quantity a substance much more strongly radioactive than either uranium or thorium.  This substance could not be one of the known elements, because these had already been examined; it must, therefore, be a new chemical element.[12]” 

Pierre was so intrigued by her results that he dropped his research and joined her studies.  For the next several years they worked side by side sometimes even filling in different sides of the same notebook! By July of 1898 the Curies published that there must be a new radioactive material that they named Polonium after Poland. 

Marie and Pierre decided to work with ore pitchblende, which was a uranium ore that was about four times more radioactive than pure uranium because they got a ton of it from the Austrian government who wanted to get rid of unwanted mining waste. At the same time the school where Pierre worked refused to let them use any large research area but did let them use an old abandoned shed that used to be the school of medicine’s dissecting room! 

“Its glass roof did not afford complete shelter against rain; the heat was suffocating in summer… There was no question of obtaining the needed proper apparatus in common use by chemists.  We simply had some old pine wood tables with furnaces and gas burners.[13]”  “Yet,” Marie recalled years later, “it was in this miserable old shed that we passed the best and happiest years of our life.[14]” 

By December they had found another substance hidden in the ore, and this one they called Radium (after radiation).  Now the race was on to try to isolate these new elements (radium and/or polonium) by doing various chemical processes and seeing if the products had higher or lower radioactivity. 

They thought it would be easy, “perhaps a few weeks would suffice to solve the problem,[15]” instead it took almost four years to partially isolate radium.  One of the problems was that it took a lot of ore to produce a tiny amount of radium and polonium decays very quickly.[In fact, Marie didn’t completely isolate Radium until 1910 and she never isolated Polonium.]

In 1902 Marie and Pierre managed to get 1/10th of a gram of radium-chloride salt from several tons of ore.  The salt turned out to be fascinating.  The Curies found that it was a million times more radioactive than uranium[16]!  In addition, radium would naturally glow. 

Marie recalled how she and Pierre enjoyed working at night when, “the feebly luminous silhouettes of the bottles or capsules containing our products… looked like faint, fairy lights.[17]”It’s terrifying isn’t it?  They really had no idea how dangerous radium was!  Well over 100 years later, their notebook is still so radioactive that you are required to wear protective clothing to touch it!  Even her cookbooks and furniture are still tainted.  And Marie and Pierre’s bodies are buried in lead lined boxes so that visitors can honor them unharmed!

They didn’t know that radium was dangerous, but they could immediately tell that it produced heat, a lot of heat.  Marie found that, “radium can melt in an hour its weight in ice[18]”! 

Even though radium was producing this heat continuously, the radium didn’t seem to change in shape or weight.  On June 25, 1903, Marie Sklodowska Curie published her findings in her Ph.D. thesis, where the committee told her she had produced, “the greatest scientific contribution ever made in a doctoral thesis[19]” 

Around that same time Marie started to think that maybe radioactivity, “is due to a transformation… in the atom itself,” although if that was true Marie worried that, “we should be forced to abandon the theory of the invariability of atoms, which is at the foundation of modern chemistry.[20]

One of the problems with understanding radiation is that in the early 1900s, no one had any idea what atoms were made of or how they worked.  Electrons had been discovered in 1897, but no one had any idea about protons or a nucleus, let alone how a nucleus could decay. 

It was actually Marie and Pierre’s discovery of Radium that led a boisterous kiwi to accidentally discover the nucleus while bombarding gold foil with radiation.  How Ernest Rutherford discovered we are almost completely nothing is next time on the lightning tamers.

“But if the nature of the radiation is actually better known, the cause of this spontaneous radiation remains a mystery, and the phenomena always presents itself to us as a profound and wonderful enigma.[21]

Curie: “A great discovery does not issue from a scientist’s brain ready-made, like Minerva springing fully armed from Jupiter’s head; it is the fruit of an accumulation of preliminary work”


[1] Sklodowska, Maria to Henrietta Dec 10, 1885 referenced in Nelson, Craig The Age of Radiance… p. 16

[2] Sklodowska, Maria to Henrietta April 4, 1887 referenced in Nelson, Craig The Age of Radiance… p. 16

[3] Sklodowska, Maria to Sklodowska, Joseph, October 1888 quoted in Curie, Eve Madame Curie p. 15?

[4] Sklodowska, Maria to Sklodowska, Bronya, March 12, 1890 quoted in Curie, Eve Madame Curie p. 17?

[5] Curie, Pierre quoted by Curie, Marie Pierre Curie p 73

[6]Becquerel, Henri “On the Rays Emitted by Phosphorescence” Feb 24, 1896 ComptesRendus122, 420 (1896) p?

[7]Becquerel “On the Invisible Rays Emitted by Phosphorescent Bodies” ComptesRendus122, 501 (1896) p??

[8]Becquerel “On the Invisible Rays Emitted by Phosphorescent Bodies” ComptesRendus122, 501 (1896) p??

[9]Becquerel “On the Invisible Rays Emitted by Phosphorescent Bodies” ComptesRendus122, 501 (1896) p??

[10] Curie, Marie “Radium and Radioactivity” Century Magazine (January 1904) pp. 461-466

[11] Curie, Marie Radio-active Substances 1904 p. 14

[12] Curie, Marie Pierre Currie p. 97

[13] Curie, Marie Pierre Currie p. 186

[14] Curie, Marie Pierre Currie p. 186

[15] Curie, Marie “Radium and Radioactivity” Century Magazine (January 1904) pp. 461-466

[16] Curie, Marie “Radium and Radioactivity” Century Magazine (January 1904) pp. 461-466

[17] Curie, Marie Pierre Currie p. 187

[18] Curie, Marie “Radium and Radioactivity” Century Magazine (January 1904) pp. 461-466

[19]quoted in Borzendowski, Janice Marie Curie: Mother of Modern Physics p. 67

[20] Curie, Marie “Radium and Radioactivity” Century Magazine (January 1904) pp. 461-466

[21] Curie, Marie Radio-active Substances 1904 p. 92

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