Incoming links: Gamma ray
These must have been gamma rays.
Just before he left Cambridge for Montreal in 1898, Rutherford conducted a simple, systematic experiment to study the absorption of rays from uranium. [...] In 1901 he determined that Becquerel's rays are indeed electromagnetic rays. He called them γ (gamma) rays.
This terminology is used e.g. in Marie Curie's Polonium paper:
Some minerals containing uranium and thorium (pitchblende, chalcolite, uranite) are very active from the point of view of the emission of Becquerel rays.
Most commonly known as a byproduct radioactive decay.
Their energy is very high compared example to more common radiation such as visible spectrum, and there is a neat reason for that: it's because the strong force that binds nuclei is strong so transitions lead to large energy changes.
A decay scheme such as Figure "caesium-137 decay scheme" illustrates well how gamma radiation happens as a byproduct of radioactive decay due to the existence of nuclear isomer.
Gamma rays are pretty cool as they give us insight into the energy levels/different configurations of the nucleus.
They have also been used as early sources of high energy particles for particle physics experiments before the development of particle accelerators, serving a similar purpose to cosmic rays in those early days.
But gamma rays they were more convenient in some cases because you could more easily manage them inside a laboratory rather than have to go climb some bloody mountain or a balloon.
The positron for example was first observed on cosmic rays, but better confirmed in gamma ray experiments by Carl David Anderson.
This is the papaer where Marie Curie announced the discovery of Polonium.
Here's a link with OCR on the French Wikisource: fr.wikisource.org/wiki/%C5%92uvres_de_Pierre_Curie/23. It's from a 1908 collection of works, but it is the exact same paper.
Here's an English translation: web.lemoyne.edu/~giunta/curiespo.html
First a recap of previous work:Note the cute terminology "Becquerel rays", which were only later understood to be electromagnetic radiation now known as gamma rays.
Some minerals containing uranium and thorium (pitchblende, chalcolite, uranite) are very active from the point of view of the emission of Becquerel rays. In a previous work, one of us showed that their activity is even greater than that of uranium and thorium, and expressed the opinion that this effect was due to some other very active substance contained in small quantities in these minerals.
Then some more recapitulation of the previously discussed groundbreaking idea that only atom counts matter for radioactivity, regardless of their chemical configuration as in fluorescence:
The study of compounds of uranium and thorium had shown, in fact, that the property of emitting rays which make air conductive and which act on photographic plates is a specific property of uranium and thorium which is found in all compounds of these metals, all the more weakened as the proportion of active metal in the compound is itself lower. The physical state of the substances seems to have a completely secondary importance. Various experiments have shown that the state of mixture of the substances seems to act only by varying the proportion of active bodies and the absorption produced by the inert substances. Certain causes (such as the presence of impurities) which act so powerfully on phosphorescence or fluorescence are therefore here completely without action. It therefore becomes very probable that if certain minerals are more active than uranium and thorium, it is because they contain a substance more active than these metals.
Then the key innovation: they used radioactivity measures to guide their purification work:
We have sought to isolate this substance in pitchblende, and experience has confirmed the above predictions.Our chemical research has been constantly guided by the control of the radiant activity of the products separated at each operation. Each product is placed on one of the plates of a condenser, and the conductivity acquired by the air is measured using an electrometer and a piezoelectric quartz, as in the work cited above. We thus have not only an indication but a number which accounts for the richness of the product in active substance.
Next they describe in high level their separation process, and I can't understand anything. But that's OK
Finally towards the end, bombs are dropped:
- the new elemnt is next to bismuth. If you stop now and look at a periodic table, you will see that bismuth is exactly one element before polonium
- "simple bodies" is their cute terminology for atoms, whose existence at the time not yet full aknowledged Section "History of the atomic theory"
- we call it polonium
By carrying out these various operations, we obtain increasingly active products. Finally, we obtained a substance whose activity is about 400 times greater than that of uranium.We have sought, among the bodies currently known, to see if there are any active ones. We have examined compounds of almost all simple bodies; thanks to the great kindness of several chemists, we have had samples of the rarest substances. Uranium and thorium are the only ones clearly active, tantalum is perhaps very weakly so.We therefore believe that the substance that we have removed from the pitchblende contains a metal not yet reported, close to bismuth by its analytical properties. If the existence of this new metal is confirmed, we propose to call it polonium, from the name of the country of origin of one of us.
They managed to purify it enough to look at the emission spectrum and it seems novel:
Mr. Demarçay was kind enough to examine the spectrum of the body that we are studying. He was unable to distinguish any characteristic line apart from those due to impurities. This fact does not support the idea of the existence of a new metal. However, Mr. Demarçay pointed out to us that uranium, thorium and tantalum offer particular spectra, formed of innumerable lines, very fine, difficult to perceive.
And once again, our radiation-based analytical chemistry technique is new:
Allow us to note that if the existence of a new element is confirmed, this discovery will be uniquely attributable to the new method of detection that Becquerel rays provide.
