How many bench chemists can say they are filling in the pages of history with their experimentations? While archeologists and geologists usually get to claim that level of fun, Pacific Northwest National Laboratory (PNNL)’s Brittany Robertson is a rare exception.
Robertson, a chemist and doctoral student who works at the national lab, is currently working on a project to confirm the history of uranium samples that are believed to be from nuclear programs in Nazi Germany.
To do so, Robertson has modified some existing forensic-based analytical techniques, and turned to radiochronometry, or the measurement of radioactive materials and their decay products to determine the ''age'' of the material. In this case, Robertson is measuring the products produced from the decay of uranium in a single mass, using mathematical relationships to evaluate if the age is consistent with the years during which Nazi Germany was performing nuclear research.
“This ends up being not only a really fun set of science experiments but also a history project where we are looking for different information, and archived info, and even letters between scientists to figure out what we can measure and how we can make some interpretations,” said Robertson during her presentation of the research at the hybrid in-person/virtual American Chemical Society Fall 2021 meeting.
Scouring the literature, Robertson determined she could analyze the surface coating of the cubes, which measure about 5 cm and just under 2 kg, in a minimally invasive way.
According to history, there were two groups of scientists in Nazi Germany working to exploit nuclear fission to produce plutonium from uranium for the country’s weapons program. One team was heralded by Werner Heisenberg (yes, the Heisenberg behind the uncertainty principle) in Berlin, while the second was led by Kurt Diebner in Gottow. Previous literature indicates that Heisenberg’s program used a cyanide-based coating to prevent oxidation of the uranium while it was in use, whereas Diebner’s group used a styrene-based coating.
“The question became, ‘could either of these organic coatings have survived over the last 80 or so years, and if it did survive, can we measure it’?,” said Robertson.
To answer that, Robertson removed about 10 mg of oxidized uranium flakes from the surface layer of one of three uranium cubes in the possession of PNNL and its collaborators. Upon analysis, the team detected the presence of styrene, which indicates that specific cube was a part of Diebner’s program at some point in history.
“To be honest, I thought it was a long shot,” said Robertson. “I didn’t think the organic would last sitting next to uranium metal for this many decades and still be detectable.”
The team plans to extract 10 mg from the two other cubes this week to test for cyanide and styrene. Of course, since these cubes are historical, the researchers can only leverage a limited amount of sample—200 mg at the most.
Between the two German programs, there were thought to be between 1,000 and 1,200 uranium cubes. Today, 12 remain in the hands of private collectors and research institutions like PNNL.
“Several of them have been lost to history, which is somewhat fun to say,” said Robertson.
The chemist is still working to refine the current radiochronometry technique to better separate and quantify the elements in PNNL’s cube, as well as adapt the method to analyze rare-earth element impurities in the object. This information could reveal where the uranium was originally mined.
Beyond history, the research team hopes the techniques being developed and refined for this project will have an impact on future work.
“Our intention to hone some of the new technologies for nuclear forensic science in hopes that those techniques go on to be applied to real nuclear forensic investigations,” said Jon Schwantes, nuclear security lead at PNNL and the project’s principal investigator. “Our science provides us an opportunity to enhance what is currently possible. It provides us a really interesting opportunity to demonstrate that science to the broader scientific community and the public as a whole.”
Photo: Brittany Robertson with PNNL’s cube, which is housed in a double-encapsulated protective case with foam inserts. Credit: Andrea Starr/PNNL