Francium is an extreme element. It is, with cesium, the largest atom in the periodic table. It has the shortest half-life of all naturally occurring elements – half is gone after just 22 minutes. And it is one of the rarest elements – it is estimated that there are 30 to 550 grams of it on Earth at any time. Furthermore, because it is so scarce and volatile, francium is one of the last discovered natural elements. It first showed itself 85 years ago.
Shortly after Christmas 1938, French laboratory technician Marguerite Perey completed the purification of the element actinium from uranium ore at the Radium Institute in Paris. For Perey, this complex purification process was routine. She had been doing it for almost ten years. First as a personal assistant to two-time Nobel Prize winner Marie Curie and after Curie’s death as a laboratory technician under the chemists André Debierne and Irène Joliot-Curie, Curie’s daughter.
Despite her experience with the radioactive actinium, the material surprised her in late 1938 by emitting an unexpected type of radiation. 29-year-old Perey was fascinated.
In January 1939 she came to the conclusion that actinium did not simply decay to thorium, which was known. Very occasionally – in just over 1 percent of cases – it appeared to decay to a substance that had not been observed before: element 87.
Perey had found a needle in a haystack: actinium produces only a tiny amount of francium and after 22 minutes half of it has disappeared. The largest amount of francium to ever exist simultaneously in an experiment is just over 300,000 atoms. That seems like a lot, but it is an invisible fraction of a microgram.
Perey wanted to get a PhD for her discovery, but she didn’t even have a bachelor’s degree. She solved that problem by studying at the Sorbonne during the Second World War. She received her PhD in 1946. She was recognized as the discoverer of element 87 and was allowed to choose a name.
Easy escape
Initially, Perey wanted to name the element catium (or katium), referring to the term cation, which denotes atoms that lack electrons and are therefore positively charged. Element 87 could easily become a cation, because it is relatively large – for an atom – which means that the electrons are far from the atomic nucleus and can therefore easily escape. Joliot-Curie advised Perey to choose a different name, as she did not want the element to be associated with cats. It became francium, after Perey’s native France.
Because francium is very rare and unstable, it has no uses. Perey did look for this as principal researcher in nuclear chemistry at the University of Strasbourg. She hoped that element 87 could be used to diagnose cancer. That never worked and Perey died at the age of 75 from bone cancer, probably caused by her years of work with radioactive substances.
In addition to the discovery of an element, Perey also has an early death due to radioactive radiation in common with her mentor Curie.