History of the discovery of rare earth elements. Element 61

In 1914, the English physicist G. Moseley reported that he had discovered a pattern linking the frequency of the spectral lines of characteristic X-ray radiation with the atomic number of an element in the periodic table. He found that there are unfilled positions in the periodic table, for example between neodymium and samarium (element 61). Information about an undiscovered element number 61 prompted many scientists to search for this element. In 1926, University of Illinois researchers J. A. Harris, L. F. Yntema, and B. S. Hopkins announced the discovery of element 61, which they named “illinium.” However, scientists L. Rolla and L. Fernandez from the University of Florence disputed their priority in discovering this element. According to the Italian researchers, they deposited two articles on the discovery of element 61, which they named “florentium,” in sealed envelopes at the Accademia Nazionale dei Lincei back in June 1924. In addition to the disagreement regarding the priority in the discovery, there were also doubts about the very fact of discovering the new element. In 1934, the German chemist Ida Noddack published her research on the existence of element 61. As a result of her work, no signs of the presence of element 61 in minerals were found. Ida Noddack believed that her research should have been able to detect with certainty an element that would have a concentration in the material 10 million times lower than the concentrations of its neighbors neodymium and samarium. A possible reason for the absence of this element, according to Ida Noddack, could be its instability. In 1934, the German physicist Josef Mattauch formulated his isobar rule, according to which only unstable radioactive isotopes were possible for element 61, which made it possible to explain the great rarity of this element. By the mid-1930s, physicists began to master the production of artificial radionuclides using nuclear reactions. In 1938, it was announced that 15 new isotopes of rare earth elements had been produced by bombarding rare earth targets with neutrons and deuterons. The researchers believed that they had, among other things, succeeded in obtaining the isotope of element 61 for the first time. Physicists proposed to give element 61 a new name, “cyclonium”, taking into account the method of synthesizing new radioisotopes using a cyclotron. In 1947, scientists J. A. Marinsky, L. E. Glendenin and K. D. Coryell reported the chemical identification and discovery of element 61, for the isolation of which the method of ion-exchange chromatography was used. The name “promethium” (Pm) was proposed for the new element. On September 5, 1949, this name was officially accepted by the International Chemical Union (IUPAC). And it was not until 1968 that the presence of the isotope Pm-147 was detected in nature.