Mattauch’s rule

The discovery of technetium (Z = 43) in 1937 and of promethium (Z = 61) in 1947 filled the two gaps in the Periodic Table of the elements. These gaps had been the reason for many investigations. Application of Mattauch s rule (section 2.3) leads to the conclusion that stable isotopes of element 43 cannot exist. Neighbouring stable isotopes could only be expected for mass numbers A 93, A < 91, A = 103 and A > 105. However, these nuclides are relatively far away from the line of jd stability. The report by Noddak and Tacke concerning the discovery of the elements rhenium and masurium (1925) was only correct with respect to Re (Z = 75). The concentration of element 43 (Tc) in nature due to spontaneous or neutron-induced fission of uranium is several orders of magnitude too low to be detectable by emission of characteristic X rays of element 43, as had been claimed in the report. 

Klement 43 in the seventh subgroup of the periodic system, technetium, is the lowest atomic number radioelement. Stable, non-radioactive isotopes do not exist according to Mattauch s rule. Technetium isotopes can be produced artificially by nuclear processes. Long-lived isotopes are Tc (2.6 10 a), Tc (4.2 10 a) and Tc (2.1 10- a). The spectroscopic discovery of technetium in several fixed stars provided the first proof of stellar synthesis of heavy nuclides. Traces of Tc occur in the earth s crust where they arise mainly from spontaneous fission of... 

All the possible mass numbers between 142 and 150 are already taken by neod)Tnium (Z = 60) and samarium (Z = 62), so that no stable isotope is expected for element 61. They would all be radioactive, just as in the case of technetium (Z = 43). The Mattauch rule however was not capable of ascribing these radioactive isotopes a certain half-life. A number of uranium and thorium isotopes are also radioactive, but their half-lives are great enough so that one can still find them in nature. During that same year, in 1934, the American physicist and future Noble Prize winner, Willard Libby (1908-1980), discovered that neodymium is a (3 emitter (Libby, 1934). According to Soddy s displacement laws, this should imply that when neodymium decays, isotopes of element 61 should be formed. 

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