Boltwood, Bertram

Boltwood/ Bertram Borden (1870-1927) American nuclear chemist who studied the radioactive breakdown of elements, and first discovered how to apply the ratios of lead to uranium in geological specimens in order to calculate their age. This, and other associated methods, was to bring new standards of accuracy into geology and paleontology. He discovered the radioactive element ionium. 

The discovery of the decay chain, of course, started with the seminal work of Marie Curie in identifying and separating Ra. Through the work of the Curies and others, all the members of the decay chain were identified. An important milestone for geochronometrists was the discovery of °Th (called Ionium) by Bertram Boltwood, the Yale scientist who also made the first age determinations on minerals using the U-Pb dating method (Boltwood in 1906 established the antiquity of rocks and even identified a mineral from Sri Lanka-then Ceylon as having an age of 2.1 billion years )... 

Bertram Borden Boltwood, 1870-1927. Professor of chemistry and physics at Yale University. Discoverer of the radioactive element ionium, the parent of radium. Ionium was discovered independently at about the same time by Hahn and by Marckwald. 

Editor s outlook. Bertram Borden Boltwood, . Chem. Educ., 6, 602-4... 

On Harkins, see R.S. Mulliken, William Draper Harkins, 1873-1951, Biographical Memoirs of Members of the National Aca-damy of Science 47 (1975) 49-81 and G. B. Kauffman, William Draper Harkins (1873-1951) A controversial and neglected physical chemist, Journal of Chemical Education 62 (1985) 758-761. In a letter to Bertram Boltwood of February 28, 1921, Rutherford described Harkins as moderately sound and a man of intelligence, but added that I wish he did more experimenting and spent less time in theorising and in endeavouring to cover every possible idea. Quoted in L. Badash (ed.), Rutherford and Boltwood Letters on Radioactivity (New Haven, 1969), 343. 

As early as 1907 Bertram Boltwood had used the discovery of radioactive decay laws by Ernest Rutherford and Frederick Soddy to ascribe an age of over two billion years to a uranium mineral. In 1947 Willard Libby at the University of Chicago used the decay of to measure the age of dead organic matter. The cosmogenic radionuclide, becomes part of all living matter through photosynthesis and the consumption of plant matter. 

During the first decade of the 20th century, the apparent relationships between transformations of radioactive elements became ever more complex until a tentative resolution was reached. In 1907, Professor Bertram B. Boltwood (1870-1927), at Yale, demonstrated that a seemingly new radioactive element he named ionium, with unique decay characteristics, was generated from the loss of an a-particle during radioactive decay of uranium. In turn, ionium lost an a-particle to produce radium. The problem was that ionium was chemically identical with (could not be separated from) the known element thorium even though the two elements had different radioactive decay patterns. 

So constant and characteristic is the majestically slow decay of uranium that it can be used to measure the age of the earth. In 1907, the American chemist Bertram Borden Boltwood (1870-1927) suggested that the lead content of uranium minerals would serve as guide in this respect. If it is assumed that all the lead in the mineral originated from uranium decay, it would be easy to calculate how long a time must have elapsed to bring that amount of lead into existence. It was eventually calculated in this way that the solid crust of the earth must have been in existence for at least four billion years. 

Another strand of development came from several attempts to separate some of these new radio-elements chemically, which ended in failure. First of all, in 1907 Herbert McCoy and WiUiam Ross concluded that, in the case of thorium and radiothorium, Our experiments strongly indicate that radiothorium is entirely inseparable from thorium by chemical processes, " a comment Soddy considered the first definitive statement of the chemical inseparability of what were soon to be called isotopes. Soddy himself wrote in the same year that there seemed to be no known method of separating thorium X from mesothorium.They were in fact two isotopes of thorium. Similar cases began to multiply. Bertram Boltwood discovered the radio-element ionium, which could not be chemically separated from thorium. In another famous case, Hevesy and Paneth were asked by Rutherford to try to separate radio-lead from ordinary lead and likewise failed to do so, in spite of using 20 different chemical methods. Their work was not entirely in vain, however, since it led to the development of the use of radioactive tracers, which have become an indispensable tool in modem chemistry and biochemistry. 

These investigations uncovered the problem that some of the new elements were so similar to familiar elements that once mixed with them they could not be separated again. Thus in 1906 Bertram Borden Boltwood (1870-1927) of Yale University was unable to separate ionium (the immediate precursor of radium in the uranium series) from thorium. Similarly, Georgy Hevesy (1885-1966) was unsuccessful in his attempts to separate radium D from lead. 

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