THE HISTORY OF AN IDEA · 1940–1961
Making elements beyond uranium
Eleven elements heavier than uranium were made rather than found, and identifying them meant inventing chemistry that works on a few thousand atoms at a time.
Explore the supporting references at the foot of this article.
01
Neutron capture, then beta decay
The route to the first two transuranium elements is simple to state: add a to uranium-238, and the resulting uranium-239 beta-decays to element 93, which decays again to element 94. McMillan and Abelson established the first step in 1940 by identifying neptunium chemically; Seaborg’s group produced plutonium shortly afterwards by deuteron bombardment. What made this hard was that similar experiments in the 1930s had produced products that mimicked new elements, so the chemical identification had to be more careful than the physics.
02
A change to the table itself
The new elements did not behave as the table then predicted. If thorium sat under hafnium and uranium under tungsten, then element 94 should resemble osmium; it did not. Seaborg’s actinide proposal in 1944 placed thorium through lawrencium as a second inner-transition series parallel to the lanthanides, which reorganised the bottom of the table and, crucially, told chemists which separation methods should work. Ion-exchange columns on the lanthanides then produced americium and curium, and the elution order predicted by the analogy is how several later elements were identified.
03
Identification at the scale of single atoms
By the end of the series the quantities were vanishing. Mendelevium was announced in 1955 on the basis of seventeen atoms, identified by where they eluted from an ion-exchange column and by their . Einsteinium and fermium had already appeared unexpectedly in debris from a 1952 thermonuclear test, where an intense neutron pulse had driven uranium up the chain in a single burst. Nobelium and lawrencium arrived contested, with competing claims from Berkeley, Stockholm and Dubna that took years to resolve.
What followed
Actinide chemistry developed here now governs nuclear fuel processing, waste separation and safeguards, and plutonium-238 supplies power for spacecraft that cannot rely on sunlight.
About Plutonium-238science.nasa.gov — PlutoniumRSC Periodic Table — PlutoniumDOE — RadiumUSGS — Radium
Sources & further reading
- About Plutonium-238 ↗NASA ScienceReference explanation · Source checked
- science.nasa.gov — Plutonium ↗science.nasa.govReference explanation · Source checked
- RSC Periodic Table — Plutonium ↗Royal Society of ChemistryReference explanation · Source checked
- DOE — Radium ↗United States Department of EnergyReference explanation · Source checked
- USGS — Radium ↗United States Geological SurveyReference explanation · Source checked
Sources and further reading. What the review labels mean