Elements 93 and 94

1934 findings of Enrico Fermi and co-workers
Now I'm going to go back quickly to some of the work that I was involved in that had to do with the heavy elements, the elements beyond uranium. This in a sense began back in 1934 when Fermi and co-workers in Rome bombarded uranium with neutrons produced in a radon-beryllium source and produced a number of activities that they thought were due to transuranium elements.
Periodic Table before World War II
For example, an activity with 13 minutes half life was thought to be due to ekarhenium. According to the periodic table of that day, it was thought that the transuranium elements would fit in in this way, and element 93 would be like rhenium, ekarhenium, 94, ekaosmium, 95, ekairidium, 96, ekaplatinum, and so forth. This work was carried on by Hahn, Meitner and Strassman in Germany. They thought that they had identified a number of activities that had these properties corresponding to the periodic table of that day. Then in December of 1938, Hahn and Strassman made their momentous discovery that these radioactivities were not due to transuranium elements but were due to fission products. So we had no transuranium elements then. They had all become fission products until McMillan and Abelson, in June of 1940, reported that one of these products from the bombardment of uranium was, indeed, a transuranium element with a mass number 239 and a half life of 2.3 days.
Otto Hahn, Lise Meitner, Fritz Strassmann--1936 or 1937, EkaRe, EkaOs, EkaIr and EkaAu Hahn & Strassmann, December 1938 Discovery of Element 93
But they couldn't find the daughter, which they thought would decay by alpha particle emission because it seemed to have too long a half life. Here is a picture of Ed McMillan taken at the time of his work, and a picture of Phil Abelson taken at that time.

Edwin M. McMillan Philip Abelson

Discovery of
Element 94
Then I entered the picture. I was an instructor in chemistry and I had a co-worker, Kennedy, who was an instructor in chemistry. McMillan had started the work to look for the next element, the element with the atomic number 94. I had a graduate student, Arthur Wahl, working with me. We bombarded uranium with deuterons and we found an activity with a half life of about 2 days due to element 93, which , when it decayed, led to a daughter whose alpha particles we could detect and chemically identify. As Darleane mentioned, we chemically identified these . . . the bombardment was made on December 14, 1940 and we chemically identified it as element 94 on February 23, 1941. But most importantly, and McMillan and Abelson had already found this, element 93 didn't resemble rhenium, it was not ekarhenium, it resembled uranium. And 94, we found, didn't resemble osmium, was not ekaosmium according to the periodic table of that day, but resembled uranium. It was clear that there was another transition series beginning to operate at this point.

Glenn T. Seaborg at Geiger-Muller counter and amplifier, 1941. Joe Kennedy at 9237 San Antonio Avenue, South Gate, Christmas, 1940 Art Wahl at Washington University
Here's a picture of me taken at this time. I like to show this picture because it shows how little I've changed in the last 55 years. Here's a picture of Joe Kennedy. We went down to South Gate -- Home Gardens became South Gate by that time -- where my parents were living, at Christmas 1940 leaving our graduate student, Art Wahl, up at Berkeley to work on the products. Here is a picture of Kennedy in the backyard, Christmas day 1940, taken by my mother with her Kodak box camera. Here's a picture of Art Wahl taken at Washington University right after the war.

Helen L. Griggs and Glenn T. Seaborg, Christmas 1941 in San Francisco
The reports announcing the discovery of element 94 were typed by Ernest Lawrence's secretary, Helen Griggs, and I like to say that she was so efficient as a secretary that I began to date her. She doesn't like that characterization, and I have to admit immediately that she had other qualities. We began to go together.Here we are in San Francisco on Market Street on Christmas 1941. One of these itinerant photographers took our picture and handed me a card and if I sent in 50 cents I could get a copy, and of course I did.

Naming -- 92 Uranium (U) Uranus, 93 Neptunium (Np) Neptune, 94 Plutonium (Pu) Pluto
In that first report, we decided to name the element plutonium, just like uranium is named after Uranus, neptunium by McMillan and Abelson after Neptune, we decided to name it plutonium. We should have named it plutium, but we liked plutonium better. It just sounded better. And the symbol obviously should have been Pl, but we liked Pu better so we gave it the symbol Pu. We thought we'd be subject to a great deal of criticism after the war was over. This was our own research. We kept it secret voluntarily and then sent the information to Washington.
The Chemical Properties of Elements 94 and 93
Here is the report written on March 21, 1942 typed by Helen Griggs, held secret until after the war when it was published in the Journal of the American Chemical Society in 1948. This is where the names plutonium and neptunium were first revealed.