German scientist has work finally vindicated

November 19, 1999

She was relegated to a mere footnote in the history of science, ridiculed by her contemporaries and for the last decades of her career could only find work as a university teaching assistant, writes Steve Farrar.

But 20 years after her death, Ida Tacke's unjustly tarnished reputation may have been rescued by American and Belgian experts.

A team from the National Institute of Standards and Technology in Maryland, United States, have resolved a 74-year-old mystery by verifying the disputed results of the brilliant German physicist's most controversial experiment, the discovery of element 43.

Tacke, together with her husband Walter Noddack, claimed to have used X-ray emission analysis to detect traces of the unstable element in a sample of uranium ore in 1925, calling it masurium. She also found another of the "missing" elements, 75, that was named rhenium, a claim that was quickly verified.

But she was unable to repeat the work on masurium and then was effectively cut off from the rest of the scientific world by the rise of the Nazis in Germany and the outbreak of war.

In a very hostile political climate, her results were later called into question and the International Union of Pure and Applied Chemistry gave the credit for finding element 43, artificially created in 1937 by bombarding molybdenum with deuterium, to two Italian physicists, Carlo Perrier and Emilio Segre. They called the substance Technetium, a radioactive metal that is used in medical bone imaging.

After the war, Tacke's work was mocked and she was criticised for remaining in Germany while other scientists fled abroad. It cast a shadow over her achievements and ensured that her name never ranked alongside other great scientists of her age.

New work, however, suggests that she was right all along. At the urging of Pieter van Assche, of the University of Leuven in Belgium, John Armstrong, a research scientist in NIST's chemical sciences and technology laboratory, used sophisticated computer analysis techniques to simulate Tacke's data and check the efficacy of her technique. "We have vindicated them," he said.

Tacke had pinpointed certain uranium ores as the most likely source of the "missing" element, and then used what was then state-of-the-art X-ray emission analysis to look for its predicted spectral signature. This was found in 40 of the 100 tests her team carried out.

Critics later remarked that her method could never have been sensitive enough to detect the tiny amounts of the substance present in the rock. Armstrong's calculations, however, suggest that even Tacke had grossly underestimated the sensitivity of her technique and that she had, in fact, found the element.

"We have not repeated their actual experiment, but using theoretical procedures we were able to reproduce the spectra they published in their original paper with the concentrations of the element they would have had and the procedures they followed," said Armstrong.

"It was a very elegant and clever experiment that was later unfairly discredited."

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