The History of the Trilinear Chart of the Nuclides
By 1920 Mendeleev's Periodic Table of the Elements had been revised to the format we now recognize (with a few empty slots still unfilled). Additionally, during the 1920's F. W. Aston (a student of Rutherford and the inventor of the mass spectrometry) completed the picture by spotting stable isotopes in over three-quarters of the elements.
In 1931 H. L. Johnston at Ohio State University attempted to devise a periodic arrangement of the isotopes. One of his foot notes however, explained the following, "25 new (stable) isotopes have been reported since this table was prepared several months ago."
On New Yearís Eve 1933, upon dismantling a positron experiment, the Joliot-Curies discovered three radionuclides: N-13, P-30, Si-27. These were the first artificially produced radionuclides produced by man. They proved the transmutation chemically before morning on January 1, 1934. It was confirmed at Cal Tech in February, at Berkeley in March, and on May 19th. Fermi in Rome published a description of 14 radionuclides. On the next page of the same journal H.J. Walk, an English chemist, predicted induced activity in all elements. By the end of July, Fermi further furnished experimental proof of induced activity by neutron bombardment in about 40 to 60 elements; and repeated Walkís prediction. By the time the accelerators in California were bombarding many targets with protons, deuterons and neutrons. Grosse summarized the new discoveries in a table of nuclides at the end of 1936. He plotted mass number against atomic number and listed 263 stable and 141 radioactive nuclides. Only 15 of the 91 known elements did not have at least 1 radioactive isotope.
G.T. Seaborg published a list on July 15, 1940 of induced radioactive isotopes. Seaborg listed 367 radioactive and 276 stable nuclides. The number of stable isotopes would decrease as mega year half-lives isotopes were believed to be stable isotopes.
By 1944 Robley Evans published another compilation of "more than 375 radioisotopes of every known chemical element." however; "chemical identification" of about 150 was not absolute. This issue with chemical identification requirement was becoming quite ìstickyî since many isotopes being discovered were very short-lived. Additionally, in 1944 nuclear physics and chemistry literature was no longer open. The atom bomb project had cut off publication and at the same time increased the tempo of the isotope development and investigations.
At the Manhattan District's Clinton Laboratories (later to become the Atomic Energy Commission and then the Department of Energy's Oak Ridge National Laboratory), a large variety of unreported nuclides were being studied. Analytical chemists in the project were finding so many possible reactions in any nuclear reactor irradiation that identification required immediate access to long tables of known nuclides and unknown possibilities.
William H. Sullivan, at Clinton Labs, tried to organize the rapidly changing nuclear data into an immediately visible form. Most nuclides decayed by isobaric transmutation toward stability; the isobars had to be visualized as related. Since chemical identification was required, the isotopes had to be listed in sequence. In Oak Ridge, where neutron bombardment was the prime method, a sequence of nuclides by neutron number was also required. Because the three important axes, neutron number, proton number and atomic number were equally important. Sullivan tried trilinear coordinate paper. A hexagon has three axes so he placed each nucleon in a hexagon. With the hexagons in a beehive array, a trilinear chart of the nuclides was formed. After a couple of years of work his first complete chart was in 4 colors and was 16 feet long unfolded. It contained 935 hexagons. It was out of date before the chart was printed in 1949.
For the second edition, in 1957 the words ìnuclear species' had already been replaced by the more popular "Trilinear Chart of the Nuclides." The new chart was 17 feet long unfolded, but it did not go out of date because gummed hexagonal stamps were issued periodically to keep the data up to date. By 1961, after 9 issues of gummed stamps had been distributed, the chart contained 1349 hexagons with many double and even triples isomers. But the data by now was becoming so complex that a nuclear data group (first at the National Academy of Science - NRC, then at Oak Ridge) had to go back to the tabular form. Thick volumes of Nuclear Data Sheets are still being updated and published.
After Sullivan's death in 1966, the chart was revised and simplified to display only half-life and decay data. Published in 1968 by Mallinckrodt, it contained 1447 hexagons; only 236 were of stable nuclides, however, 68 had half-lives over 1 mega year. In the 1979 revision there were 2131 filled hexagons on the chart. In the 1979 edition of the Trilinear Chart of the Nuclides, Bruce Marshall, lamented with the following words, "Depending upon how you define a separate nuclide (required length of half-life? Number of isomers?), by my definition there are 2452 nuclides, 252 are stable, 55 have half-lives over 106 y, 42 have half-lives over 100 years; there are 608 isomers and 8 hexagons show triple isomers. I have added 264 empty hexagons to fill in empty spaces that might still be filled. The new very high-energy accelerators and extremely fast detection techniques are already extending beyond the chart. But, within a more livable time scale, you can now say that matter is composed of about 300 nuclides which when stressed can be converted to about 2500 different species which will eventually decay back to about 300 nuclides. Lavoisier! That's why they cut off your head in 1789; you were wrong by a factor of 10. Let future chemists beware of scientists in high government positions."
The current chart of the nuclides published by the Radiochemistry Society in 2005 contains the latest information on half-lives or isotopic abundances, decay modes and decay energies.
The current count for this chart is 3015 isotopes (hexagons) with 249 stable isotopes.