How Many Grams of Radium Can Form by Passing
The discovery of radium
How are new elements discovered? These days, it is through deliberate, concerted effort in a known direction: the just empty spots in the periodic tabular array are all at the high terminate, at atomic numbers in a higher place 105 (or 108, or whatever the electric current value is). Physicists know that if they bombard heavy elements with energetic nuclei, they may very occasionally create a very heavy nucleus; and, if such nuclei should last long enough to build up a macroscopic sample of textile, they may measure the properties of a new element. Information technology is difficult piece of work, but follows a clear path with a well divers goal.
Back in the old days, however, life was not so simple. The periodic table was still a work in progress: there were plenty of gaps and holes, equally well as puzzling inconsistencies. More important, there was no theory to guide scientists in their piece of work: the nature of atoms and nuclei was not nonetheless understood at the plow of the twentieth century. Chemists and physicists did non know that there were exactly 30 distinct elements between hydrogen and zinc, or that helium would have exactly five siblings among the (stable) noble gases.
Let us look at the discovery of the elements polonium and radium: they were tentatively announced past the squad of Pierre Curie, Marie Curie, and Gustave Bemont in 1898. It was iv more years, withal, until Marie Curie was able to isolate a pure plenty sample of radium to measure out some of its properties.
Background: the era of invisible rays
In 1895, Wilhem Conrad Roentgen, a physicist working at the Unversity of Wurzburg in Germany, was investigating the properties of a "Crookes tube": an evacuated drinking glass tube through which a strong electric current is passed at high voltage. He noticed some curious phenomena which were somehow connected to the operation of the Crookes tube, simply took identify far from it.
Thanks to Dream Anatomy for a re-create of Roentgen's X-ray of his wife's manus.
- Read more nigh Roentgen's discoveries
Roentgen realized that invisible rays were coming from the Crookes tube, flying through the air, and interacting in novel ways with a wide variety of materials. He named the rays X-rays.
People around the world were excited by the discovery of these rays, and the fascinating properties they had. Was it possible that there could also be other "rays" in the world?
Radioactivity
Just a year later, French physicist Henri Bequerel noticed a peculiar little event: he left a modest piece of uranium (wrapped upward inside a piece of newspaper) sitting on a photographic plate in a drawer for several weeks. When, on a lark, he developed the plate, he found a dark spot at the location which had been directly under the uranium. Somehow, the uranium had exposed the photographic plate, even though it had been covered in opaque cloth. Could this be another sort of invisible ray?
In 1897, a graduate student at the Academy of Paris named Marie Curie decided to investigate one attribute of this new miracle for her doctoral dissertation. She was twenty-nine years sometime and had simply given birth to her first child, Irene, during September of that year. "What," she asked, "was the nature and origin of this radiation?" She would continue this investigation for the residue of her life. Her husband, Pierre Curie, a physicist at the University, was her partner in the piece of work until his death in 1906.
The first step was to look at the source of the radiations. Information technology was known that materials containing compounds of uranium and thorium were radioactive (a term coined past Marie Curie). The Curies decided to await harder ...
The source(south) of radioactive decay
How tin can one measure radioactivity in a quantitative manner? One instrument used by the Curies was a simple device:
Two metal plates are separated by a gap of a few centimeters of air. Marie Curie described hers as follows:
(Diameter of the plates 8 cm; distance 3 cm.) A difference of potential of 100 volts was established between the plates. The electric current which passed through the condenser was measured in accented value by means of an electrometer and a piezo-electric quartz.When a voltage is practical beyond the plates, no current runs. Why not?From "Rayons Emis par les Composes de Fifty'Uranium et du Thorium," Comptes rendus, Vol 126, April 1898
Because air isn't a conductor, of course.
However, if one can somehow change the air then that information technology Will carry electricity, then the size of the electric current will indicate the electrical conductivity (or resistivity) of the air. Bombarding the air with energetic particles can ionize some of the molecules, turning them into charged entities
which volition carry a current.
The Curies would simply cover 1 of the ii plates with some material. If no electric current ran through the system, information technology was inert ...
... merely if a current did run, then the material was radioactive. The size of the current provided a quantitative measure of the radio-activeness of the substance.
This setup produced currents which were very small: a sample of pure uranium gave a current of 24 picoamps (that's 24 x 10-12 amperes), for example.
Marie Curie reported a very puzzling outcome: pure uranium and thorium did non produce as much current as certain ores (pitchblende and chacolite) from which they were refined.
| Material | picoamps |
| Uranium | 24 |
| Black oxide of uranium | 27 |
| Hydrated uranic acid | 6 |
| Pitchblende from Johanngeorgenstadt | 83 |
| Pitchblende from Joachimstahl and from Pzibran | 67 |
| Natural chacolite | 52 |
| Bogus chacolite | (see below) |
A partial copy of the table in Rayons Emis par les Composes de L'Uranium et du Thorium
Chacolite is a mixture of copper and uranium phosphates. When Marie Curie made her ain "artificial chacolite" by combining pure samples of copper and uranium with other materials, she institute the resulting compound to have no more than radioactivity than other uranium compounds.
So, why were some of the raw materials stronger sources of radiation than pure uranium and thorium? The Curies speculated that there might exist an extra, very strongly radioactive component in the raw mixtures which was eliminated past chemical processing.
They set out to find this postulated, very radioactive substance which was hiding in the raw ores.
Naming Polonium and Radium
During 1898, the Curies continued their chemical experiments, trying always to place the portion of the uranium ore which was virtually strongly radioactive. In Dec, 1898, they announced that there were apparently 2 highly radioactive substances subconscious in the ore. They explicate:
2 of us have shown that by purely chemic processes one tin extract from pitchblende a strongly radioactive substance. This substance is closely related to bismuth in its belittling properties. We have stated the opinion that pitchblende may maybe comprise a new element for which we accept proposed the proper name polonium.The investigations which we are now following are in accord with the first results obtained, just in the course of these researches we take institute a second substance strongly radioactive and entirely unlike in its chemical properties from the first. In fact, polonium is precipitated out of acid solutions by hydrogen sulphide, its salts are soluble in acids, and water precipitates them from these solutions; polonium is completely precipitated by ammonia.
The new radioactive substance that nosotros have just found has all the chemic aspects of nearly pure barium: It is precipitated neither by hydrogen sulphide, nor ammonium sulphide, nor by ammonia; the sulphate is insoluble in acids and water; the carbonate is insoluble in water; the chloride, very soluble in water, is insoluble in concentrated hydrochloric acid and in alcohol. Finally this substance shows the hands recognized spectrum of barium
We believe nevertheless that this substance, although constituted for the greater part past barium, contains in addition a new element which gives it its radioactivity and which moreover is very close to barium in its chemical properties ...
From Sur Une Nouvelle Substance Fortement Radio-Active, Contenue Dans La Pitchblende by M. P. Curie, Mme. P. Curie and M. Thou. Bemont, Comptes rendus, Vol 127, Dec 1898.
The barium-like substance was by far the strongest source of radioactivity in the ores: they measured an activity level nine hundred times higher than that of uranium!
Let's stop for a moment to wait at the bodily levels of radio-action for samples of uranium and radium. Over periods brusk compared to the one-half-life of two substances, the relative number of decays is equal to the inverse ratio of their half-lives. Suppose we take two samples of textile, uranium and radium, with an equal number of atoms in each.
Q: What is the half-life of the about common isotope of uranium, U-238? Q: What is the half-life of radium-226? (This is produced in the sequence of decays starting from U-238) Q: What is the ratio of (number of decays from the sample of radium during a mean solar day) to (number of decays from the sample of uranium during a day)? Q: Was the Curie'southward sample of radium pure at this point in 1898? A spectrum of this very active substance, taken past Eugene Demarcay, showed a number of strong lines due to barium and atomic number 82; but at that place was likewise a strong line at a wavelength of 3814.8 Angstroms. Demarcay wrote:
It does non seem possible to me that this line can be attributed to whatever known element ... Neither barium nor lead from elsewhere [i.e. from sources other than the Curies' material], equally I have assured myself, requite any line which coincides with it.From Sur le Spectre d'une Substance Radio-Active by Chiliad. Eug. Demarcay, Comptes rendus, December 26, 1898.
The NIST Atomic Spectra Database shows a line of Ra Two (singly-ionized radium) at 3814.42 Angstroms.
The Curies suggested that this very radioactive substance might bring together polonium as a new element:
The various reasons which we have simply enumerated atomic number 82 u.s.a. to believe that the new radioactive substance contains a new chemical element to which we advise to give the name radium.From Sur Une Nouvelle Substance Fortement Radio-Active, Contenue Dans La Pitchblende by Thousand. P. Curie, Mme. P. Curie and 1000. G. Bemont, Comptes rendus, Vol 127, December 1898.
Isolating Radium
By the stop of 1898, the Curies had strong show for two new elements: polonium and radium. But before these could join the other elements accepted by the scientific community, their properties had to be measured carefully. How else could chemists and physicists distinguish the new elements from other materials?The Curies paid out of their own pockets for bags of discarded slag to be shipped to them in Paris from the mine at St. Joachimsthal (in Bohemia, northeast of Berlin).
Where could the Curies perform their chemical extractions? The University of Paris offered them an abandoned shed in one of the courtyards; the School of Medicine had used information technology as a dissecting room in the past, just it was considered unfit for cadavers in 1898. A visitor to this shed described it as follows:
I knocked at a door chosen at random and enetered a laboratory of amazing simplicity: the floor was of rugged beaten globe, the walls of ruined plaster, the ceiling of rather shaky laths, and the light came in weakly through dusty windows. .... It was cold. Drops of water were falling from a tap. Two or three gas burners were debark."Echo de Paris", by Paul Acker, quoted in Madame Curie by Eve Curie.
This image from the Autumn 2002 AIP Newsletter shows a portion of the interior, with large carboys belongings liquids used in the fractionation process.
The shed had no chimneys to comport off noxious fumes; the Curies could only open up the door to increase the breeze through the windows. It was hot in the summer and frigid in the winter; one of Marie Curie'due south notebook folio for Feb half dozen, 1898 includes the words "Temperature here half dozen.25 !!!!!!!!!!" (that's 6.25 degrees Celsius, about 44 Fahrenheit).
German pharmacist Wilhelm Ostwald visited the shed to see how the radioactive elements were being isolated. He wrote:
At my hostage request, I was shown the laboratory where radium had been discovered shortly before.... It was a cantankerous between a stable and a murphy shed, and if I had non seen the worktable and items of chemical apparatus, I would take idea that I was been played a applied joke.This anecdote taken from an article about Marie Curie'south Nobel Prize
Marie Curie later on wrote of her struggle to go along their investigations under the harsh conditions.
We had no money, no laboratory and no help in the conduct of this important and hard task. Information technology was like creating something out of nothing ... And withal it was in this miserable old shed that the best and happiest years of our life were spent, entirely consecrated to work. I sometimes passed the whole day stirring a mass in ebullition, with an iron rod well-nigh equally big every bit myself. In the evening I was cleaved with fatigue.
From The Discovery of Radium page at Lateral Science.
For month afterwards month, the Curies persisted in their quest to isolate the new elements. They were joined by Andre Debierne, who concentrated on the portions of material which were precipitated out of acrid solutions past ammonia compounds. In 1899, he announced the isolation of a third radioactive element, similar in its properties to titanium. He named this material actinium.
But radium proved more difficult to isolate. For four years, Marie Curie connected to stir, sift, heat, cool, deliquesce, precipitate and treat the radium-bearing portions of the discarded ore. Over this time, she processed near seven tons of slag from the mines in Joachimsthal, largely by her own hands. In August, 1902, she finally managed to create a relatively pure sample of radium chloride, i decigram by mass.
radium chloride 0.one g --------------- = ------------ = 1 part in fourscore million original mass eight,000,000 g With this sample, she was able to determine the atomic weight of radium to be 225, showing clearly that it must exist a new chemical element.
1 year afterward, on June 25, 1903, the Academy of Paris approved Marie Curie'south thesis research, conferring on her the title of Doctor of Physical Science, with loftier honors. Two of her iii examiners would proceed to win Nobel Prizes over the side by side five years ... but Marie crush them to information technology.
In Dec, 1903, Marie and Pierre Curie were awarded a portion of the Nobel Prize in Physics, together with Antoine Henri Becquerel. Neither was able to travel to Sweden for the ceremonies, as they were both in poor health (Marie had miscarried a child in August). They did make information technology to Stockholm eighteen months afterward, where Pierre Curie gave a Nobel lecture.
Less than a twelvemonth after this triumph, he was killed in a traffic accident, leaving behind Marie and her two immature daughters. Marie would go along to win a second Nobel Prize in Chemistry in 1911. Older girl Irene continued her family's enquiry on radioactive substances, winning the 1935 Nobel Prize in Chemistry with her husband, Frederic Joliet, for work on the transmutation of elements.
For more than data
- Rays emitted past compounds of uranium and of thorium by Mme. Sklodowska Curie, Comptes Rendus 126, Apr 1898 I found this translation at Selected Archetype Papers from the History of Chemistry compiled by Carmen Giunta at Le Moyne College.
- On a new, strongly radioactive substance, contained in pitchblende by M. P. Curie, Mme. P. Curie, and Thousand. G. Bémont, Comptes Rendus 127, 1215-vii (1898) , translated and reprinted in Henry A. Boorse and Lloyd Motz, eds., "The Earth of the Atom," vol. 1 (New York: Basic Books, 1966). This is also taken from Selected Classic Papers from the History of Chemistry
- Radium and Radioactivity by Mme. Sklodowska Curie, Century Mag, (Jan 1904), pp. 461-466.
- The Nobel Laureates site has a wealth of information most the Nobel Prize won by the Curies.
- The disuse chain of U-238 shows how radium and polonium are produced from a uranium-bearing ore.
Source: http://spiff.rit.edu/classes/phys314/lectures/radium/radium.html
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