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Most students meet nuclear fission through Otto Hahn, Fritz Strassmann, Lise Meitner and Otto Frisch. Fewer know that a German chemist described the basic idea in print more than four years before their work. Her name was Ida Noddack, and she was already known for finding a new element. This post covers her two big contributions, the nuclear arithmetic behind her argument and what students can learn from why it was ignored.
Who was Ida Noddack?
Physics Today records that she was born Ida Tacke on 25 February 1896 in Lackhausen, now part of Wesel, in Germany. By 1925 she was working in Berlin with the chemist Walter Noddack, and she later took the name Noddack. A chapter in European Women in Chemistry gives her life as 1896 to 1978.
How was rhenium discovered?
Mendeleev's table left gaps below manganese, for what we now call technetium (element 43) and rhenium (element 75). The Royal Society of Chemistry's rhenium page credits the discovery in 1925 to Walter Noddack, Ida Tacke and Otto Berg. The team reported it in a 1925 paper, "Die Ekamangane", in Die Naturwissenschaften. They named it after Rhenus, the Latin name for the Rhine. The RSC calls rhenium the last stable, naturally occurring element to be discovered.
The work was hard. In the RSC's podcast on rhenium, chemist Eric Scerri says the team processed about 660 kg of the ore molybdenite to get one gram of rhenium.
Quick check: 1 g out of 660 kg is 1 ÷ 660,000, which is about 1.5 × 10⁻⁶. That is roughly 1.5 parts per million by mass, close to the "something like 1 part per million" abundance Scerri gives for rhenium in the Earth.
The team also claimed element 43, which they called masurium. That claim was not accepted. The RSC's technetium page credits element 43 to Emilio Segrè in 1937, and notes that 1920s claims "cannot be entirely discounted".
What did Noddack say about element 93?
In 1934 Enrico Fermi's group in Rome bombarded uranium with neutrons and reported, in Nature, the possible production of elements beyond uranium. Newspapers treated element 93 as found.
Noddack replied in September 1934 in Angewandte Chemie with "Über das Element 93" (On element 93). In an English translation by H. G. Graetzer, her criticism is clear. Fermi had shown his new 13-minute activity was not one of several elements near uranium, but he had not checked every element. She ran his chemical separation on a solution of nearly all stable elements and found many of them were carried down with the precipitate. Polonium was too. So, she wrote, the proof of element 93 was "in no sense successful".
Then came the line that matters most: "When heavy nuclei are bombarded by neutrons, it is conceivable that the nucleus breaks up into several large fragments, which would of course be isotopes of known elements but would not be neighbors of the irradiated element."
Worked example: decay or fission?
Use conservation of mass number (A) and atomic number (Z).
Fermi's reading. Uranium-238 (Z = 92) absorbs a neutron to give uranium-239. If that nucleus emits a beta particle, Z rises by 1 and A stays 239. The product would be element 93, a near neighbour of uranium.
Fission. The NCERT Class 12 physics chapter Nuclei gives this reaction: a neutron plus uranium-235 forms uranium-236, which splits into barium-144, krypton-89 and 3 neutrons.
Check A: 1 + 235 = 236, and 144 + 89 + 3 × 1 = 236. Balanced.
Check Z: 0 + 92 = 92, and 56 + 36 + 0 = 92. Balanced.
Barium (Z = 56) is 36 places away from uranium. That is exactly the kind of "not a neighbour" product Noddack described.
Common mistakes: forgetting the free neutrons when you add up A; giving neutrons a charge when you add up Z; assuming a product must sit next to uranium in the table.
When was fission confirmed?
In January 1939 Otto Hahn and Fritz Strassmann reported in Die Naturwissenschaften that irradiated uranium gave alkaline earth metals. The Nobel Prize facts page for Hahn's 1944 Chemistry prize says they created barium, which Meitner and Frisch then explained as a split nucleus. Hahn's prize motivation reads: "for his discovery of the fission of heavy nuclei". Our post on Lise Meitner and fission tells that side of the story.
Why was Noddack's idea ignored?
No single answer is agreed. In the RSC podcast, Scerri says the most popular view is that the doubtful element 43 claim had damaged her reputation. Her paper also offered the idea only as a possibility, without an experiment to test it.
What can a student take from Noddack's way of working?
Check the method, not just the headline. She tested Fermi's separation on almost every element before judging it.
List the other explanations. Her fission idea came from asking what else could fit the data.
Back ideas with tests. An idea without an experiment is easy to ignore, even when it is right.
Expect mixed results. The same team was right about rhenium and wrong about element 43.
If nuclear reactions still feel like a list of formulas, the Fermi Concept Library covers every concept in physics, chemistry, biology, mathematics and computing, so you can check the ideas behind each step. For energy figures, see our guide to fission and fusion energy.
Try it now: balance a neutron plus uranium-235 giving antimony-133 (Z = 51), niobium-99 (Z = 41) and some neutrons, and find how many neutrons come out.
