by John Carey
Becquerel thus became the first human being to observe the phenomenon later known as radioactivity, and to discover that uranium was a radioactive element.
Source: A Source Book in Physics, ed. W. F. Magie, New York, McGraw Hill, 1935.
The Colour of Radium
In 1897 Becquerel’s paper on radiation (see p. 188) was read by a young scientist looking for a doctoral-thesis subject, Marie Curie. Born in Warsaw in 1867, she was the youngest of five children of two Polish intellectuals. She attended the ‘Floating University’ run by Polish teachers in defiance of their Russian rulers, and espoused forward-looking movements – socialism, positivism, science.
In 1891, after a six-year stint as a governess, she went to Paris and enrolled at the Sorbonne. As a student she led a life of monastic simplicity, surviving mainly on tea and bread-and-butter. She came top in the Master’s degree in Physics in 1893, and‚ two years later, married a shy, unworldly young research chemist, Pierre Curie. They rented a tiny flat up four flights of stairs and devoted themselves to science.
It was at this point that Marie read Becquerel’s paper, and decided to investigate radiation for her doctorate. She worked in a damp, glassed-in lumber room in the Rue Lhomond – the only space the School of Physics could find for her. Her first discovery was that uranium was not the only chemical element capable of radiation. Another element, thorium, also emitted spontaneous ‘rays’. She gave this phenomenon the name ‘radioactivity’. She then found that certain minerals containing uranium and thorium (pitch-blende, chalcolite, uranite) were much more radioactive than the amount of uranium and thorium in them could account for. There must, she concluded, be another highly radioactive substance present, and she formed the hypothesis that this was a previously undiscovered element.
She determined to isolate this, and in May 1898 her husband Pierre joined her in the search. They found that radioactivity was concentrated principally in two different chemical fractions of pitch-blende, indicating the presence of two new elements, not one. By July they were able to announce the discovery of the first, which they called ‘polonium’ (‘from the name’ as they explained, ‘of the original country of one of us’).
In her biography of her mother, assembled from letters, diaries and conversations, Marie’s daughter Eve Curie has left a vivid impression of her parents’ life during this momentous period.
Life was unchanged in the little flat in the Rue de la Glacière. Marie and Pierre worked even more than usual: that was all. When the heat of summer came, the young wife found time to buy some baskets of fruit in the markets and, as usual, she cooked and put away preserves for the winter, according to the recipes used in the Curie family. Then she locked the shutters on her windows, which gave on burnt leaves; she registered their two bicycles at the Orleans station, and, like thousands of other young women in Paris, went off on holiday with her husband and her child.
This year [1898] the couple had rented a peasant’s house at Auroux, in Auvergne. Happy to breathe fresh air after the noxious atmosphere of the Rue Lhomond, the Curies made excursions to Mende, Puy, Clermont, Mont-Dore. They climbed hills, visited grottoes, bathed in rivers. Every day, alone in the country, they spoke of what they called their ‘new metals’, polonium and ‘the other’ – the one that remained to be found. In September they would go back to the damp workroom and the dull minerals; with freshened ardour they would take up their search again….
In spite of their prosaic character – or perhaps because of it – some notes written by Mme Curie in that memorable year 1898 seem to us worth quoting. Some are to be found in the margins of a book called Family Cooking, with respect to a recipe for gooseberry jelly:
I took eight pounds of fruit and the same weight in crystallised sugar. After boiling for ten minutes, I passed the mixture through a rather fine sieve. I obtained fourteen pots of very good jelly, not transparent, which ‘took’ perfectly.
In a school notebook covered with grey linen, in which the young mother had written little Irène’s weight day by day, her diet and the appearance of her first teeth, we read under the date of July 20th, 1898, some days after the publication of the discovery of polonium:
Irène says ‘thanks’ with her hand. She can walk very well now on all fours. She says ‘Gogli, gogli, go.’ She stays in the garden all day at Sceaux on a carpet. She can roll, pick herself up, and sit down.
On August 15th, at Auroux:
Irène has cut her seventh tooth, on the lower left. She can stand for half a minute alone. For the past three days we have bathed her in the river. She cries, but today (fourth day) she stopped crying and played with her hands in the water.
She plays with the cat and chases him with war cries. She is not afraid of strangers any more. She sings a great deal. She gets up on the table when she is in her chair.
Three months later, on October 17th, Marie noted with pride: ‘Irène can walk very well, and no longer goes on all fours.’
On January 5th, 1899: ‘Irène has fifteen teeth!’
Between these two notes – that of October 17th, 1898, in which Irène no longer goes on all fours, and that of January 5th, in which Irène has fifteen teeth – and a few months after the note on the gooseberry preserve, we find another note worthy of remark.
It was drawn up by Marie and Pierre Curie and a collaborator called G. Bémont. Intended for the Academy of Science, and published in the Proceedings of the session of December 26th, 1898, it announced the existence of a second new chemical element in pitch-blende.
Some lines of this communication read as follows:
The various reasons we have just enumerated lead us to believe that the new radioactive substance contains a new element to which we propose to give the name of RADIUM.
The new radioactive substance certainly contains a very strong proportion of barium; in spite of that its radioactivity is considerable. The radioactivity of radium, therefore, must be enormous.
Radium was present in pitch-blende in almost negligible quantities – one part to approximately ten million parts of the ore. To extract it, establish its atomic weight, and convince the many scientists who doubted the existence of the new element, was the huge task the Curies set themselves. Obtaining pitch-blende was an initial obstacle. It was a costly ore, treated at the St Joachimsthal mine in Bohemia for the extraction of uranium salts used in the manufacture of glass. The residue of this process was piled up in a no-man’s-land, planted with pine trees, near the mine. The Curies worked out that polonium and radium would still be present in this slag-heap, and the Austrian government agreed to give the two French ‘lunatics’ a ton of it. Further supplies had to be paid for from their meagre savings. The dull brown ore arrived, still mixed with pine-needles, in sacks on a coal wagon, and the Curies processed it in an abandoned shed at the School of Physics that had replaced Marie’s lumber room. Since the shed had no chimney to carry off noxious fumes, much of the work had to be done in the courtyard outside. ‘I sometimes passed the whole day’, Marie later wrote, ‘stirring a boiling mass, with an iron rod nearly as big as myself. In the evening I was broken with fatigue.’ The Curies worked for four years in these conditions, from 1898 to 1902. Determining the properties of radium was Pierre’s allotted task; Marie’s was extracting salts of pure radium from the ore. As her daughter explains:
In this division of labour Marie had chosen the ‘man’s job’. She accomplished the toil of a day labourer. Inside the shed her husband was absorbed by delicate experiments. In the courtyard, dressed in her old dust-covered and acid-stained smock, her hair blown by the wind, surrounded by smoke which stung her eyes and throat, Marie was a sort of factory all by herself.
I came to treat as many as twenty kilogrammes of matter at a time [she writes], which had the effect of filling the shed with great jars of precipitates and liquids. It was killing work to carry the receivers, to pour off the liquids and to stir, for hours at a stretch, the boiling matter in a smelting basin.
Radiu
m showed no intention of allowing itself to be known by human creatures. Where were the days when Marie naïvely expected the radium content of pitch-blende to be one per cent? The radiation of the new substance was so powerful that a tiny quantity of radium, disseminated through the ore, was the source of striking phenomena which could be easily observed and measured. The difficult, the impossible thing was to isolate this minute quantity, to separate it from the gangue in which it was so intimately mixed.
The days of work became months and years: Pierre and Marie were not discouraged. This material, which resisted them, which defended its secrets, fascinated them. United by their tenderness, united by their intellectual passions, they had, in a wooden shack, the ‘anti-natural’ existence for which they had both been made, she as well as he.
At this period we were entirely absorbed by the new realm that was, thanks to an unhoped-for discovery, opening before us [Marie was to write]. In spite of the difficulties of our working conditions, we felt very happy. Our days were spent at the laboratory. In our humble shed there reigned a great tranquillity: sometimes, as we watched over some operation, we would walk up and down, talking about work in the present and in the future; when we were cold a cup of hot tea taken near the stove comforted us. We lived in our single preoccupation as if in a dream.
Whenever Pierre and Marie, alone in this poor place, left their apparatus for a moment and quietly let their tongues run on, their talk about their beloved radium passed from the transcendent to the childish.
‘I wonder what It will be like, what It will look like,’ Marie said one day with the feverish curiosity of a child who has been promised a toy. ‘Pierre, what form do you imagine It will take?’
‘I don’t know,’ the physicist answered gently. ‘I should like it to have a very beautiful colour …’
For the Congress of Physics of 1900, the Curies drew up a general report on radioactive substances that aroused great interest among European scientists. Other researchers and technicians joined them in their laboratory. The direction and execution of the project remained, however, their own.
Marie continued to treat, kilogramme by kilogramme, the tons of pitch-blende residue which were sent her on several occasions from St Joachimsthal. With her remarkable patience she was able to be, every day for four years, physicist, chemist, specialised worker, engineer and labouring man all at once. Thanks to her brain and muscle, the old tables in the shed held more and more concentrated products – products richer and richer in radium. Mme Curie was approaching the end: she no longer stood in the courtyard, enveloped in bitter smoke, to watch the heavy basins of material in fusion. She was now at the stage of purification and of the ‘fractional crystallisation’ of strongly radioactive solutions. But the poverty of her haphazard equipment hindered her work more than ever. It was now that she needed a spotlessly clean workroom and apparatus perfectly protected against cold, heat and dirt. In this shed, open to every wind, iron- and cold-dust was afloat which, to Marie’s despair, became mixed with the products purified with so much care. Her heart sometimes constricted before these little daily accidents, which absorbed so much of her time and her strength.
Pierre was so tired of the interminable struggle that he would have been quite ready to abandon it. Of course, he did not dream of dropping the study of radium and of radioactivity. But he would willingly have renounced, for the time being, the special operation of preparing pure radium. The obstacles seemed insurmountable. Could they not resume this work later on, under better conditions? More attached to the meaning of natural phenomena than to their material reality, Pierre Curie was exasperated to see the paltry results to which Marie’s exhausting effort had led. He advised an armistice.
He counted without his wife’s character. Marie wanted to isolate radium and she would isolate it. She scorned fatigue and difficulties, and even the gaps in her own knowledge which complicated her task. After all, she was only a very young scientist: she still had not the certainty and great culture Pierre had acquired by twenty years’ work, and sometimes she stumbled across phenomena or methods of calculation of which she knew very little and for which she had to make hasty studies.
So much the worse! With stubborn eyes under her great brow, she clung to her apparatus and her test-tubes.
In 1902, forty-five months after the day on which the Curies announced the probable existence of radium, Marie finally carried off the victory in this war of attrition: she succeeded in preparing a decigramme of pure radium, and made a first determination of the atomic weight of the new substance, which was 225.
The incredulous chemists – of whom there were still a few – could only bow before the facts, before the superhuman obstinacy of a woman.
Radium officially existed.
*
It was nine o’clock at night. Pierre and Marie Curie were in their little house at 108 Boulevard Kellermann, where they had been living since 1900. The house suited them well. From the boulevard, where three rows of trees half hid the fortifications, could be seen only a dull wall and a tiny door. But behind the one-storey house, hidden from all eyes, there was a narrow provincial garden, rather pretty and very quiet. And from the ‘barrier’ of Gentilly they could escape on their bicycles toward the suburbs and the woods….
Old Dr Curie, who lived with the couple, had retired to his room. Marie had bathed her child and put her to bed, and had stayed for a long time beside the cot. This was a rite. When Irène did not feel her mother near her at night she would call out for her incessantly, with that ‘Mé!’ which was to be our substitute for ‘Mamma’ always. And Marie, yielding to the implacability of the four-year-old child, climbed the stairs, seated herself beside her and stayed there in the darkness until the young voice gave way to light, regular breathing. Only then would she go down again to Pierre, who was growing impatient. In spite of his kindness, he was the most possessive and jealous of husbands. He was so used to the constant presence of his wife that her least eclipse kept him from thinking freely. If Marie delayed too long near her daughter, he received her on her return with a reproach so unjust as to be comic:
‘You never think of anything but that child!’
Pierre walked slowly about the room. Marie sat down and made some stitches on the hem of Irène’s new apron. One of her principles was never to buy ready-made clothes for the child: she thought them too fancy and impractical. In the days when Bronya was in Paris the two sisters cut out their children’s dresses together, according to patterns of their own invention. These patterns still served for Marie.
But this evening she could not fix her attention. Nervous, she got up; then, suddenly:
‘Suppose we go down there for a moment?’
There was a note of supplication in her voice – altogether superfluous, for Pierre, like herself, longed to go back to the shed they had left two hours before. Radium, fanciful as a living creature, endearing as a love, called them back to its dwelling, to the wretched laboratory.
The day’s work had been hard, and it would have been more reasonable for the couple to rest. But Pierre and Marie were not always reasonable. As soon as they had put on their coats and told Dr Curie of their flight, they were in the street. They went on foot, arm in arm, exchanging few words. After the crowded streets of this queer district, with its factory buildings, wastelands and poor tenements, they arrived in the Rue Lhomond and crossed the little courtyard. Pierre put the key in the lock. The door squeaked, as it had squeaked thousands of times, and admitted them to their realm, to their dream.
‘Don’t light the lamps!’ Marie said in the darkness. Then she added with a little laugh:
‘Do you remember the day when you said to me: “I should like radium to have a beautiful colour”?’
The reality was more entrancing than the simple wish of long ago. Radium had something better than ‘a beautiful colour’; it was spontaneously luminous. And in the sombre shed, where, in the absence of cupboards, the precious particles in their tiny glass recei
vers were placed on tables or on shelves nailed to the wall, their phosphorescent bluish outlines gleamed, suspended in the night.
‘Look … Look!’ the young woman murmured.
She went forward cautiously, looked for and found a straw-bottomed chair. She sat down in the darkness and silence. Their two faces turned toward the pale glimmering, the mysterous sources of radiation, toward radium – their radium. Her body leaning forward, her head eager, Marie took up again the attitude which had been hers an hour earlier at the bedside of her sleeping child.
Her companion’s hand lightly touched her hair.
She was to remember for ever this evening of glow-worms, this magic.
From 1900 onwards the Curies had been in correspondence with scientists from all over the world, responding to requests for information. Research workers from other countries joined the search for unknown radioactive elements. In 1903 two English scientists, Ramsay and Soddy, demonstrated that radium continually disengaged a small quantity of gas, helium. This was the first known example of the transformation of atoms. A little later Rutherford and Soddy, taking up a hypothesis considered by Marie Curie as early as 1900, published their Theory of Radioactive Transformation, affirming that radioactive elements, even when they seemed unchangeable, were in a state of spontaneous evolution. Of this Pierre Curie wrote: ‘Here we have a veritable theory of the transformation of elements, but not as the alchemists understood it. Inorganic matter must have evolved through the ages, following immutable laws.’