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75 Years of atom splitting: on Christmas day in 1938, Lise Meitner and Otto Frisch took a famous walk in the snow in Sweden and solved the mystery--the "strange results" were actually the smaller products of uranium splitting, a process that Frisch coined "fission".

Seventy-five years ago, in February 1939, the first technical explanation for nuclear fission was published in the journal "Nature", heralding a new era of science with almost immediate ties to industrial, military, and civilian development. The paper, by Lise Meitner and her nephew Otto Frisch (both Jewish physicists exiled from pre-war Germany) ended half a decade of confusion in the world of nuclear physics, starting in 1934 when Enrico Fermi first experimentally bombarded uranium with neutrons (a type of subatomic particle) and incorrectly interpreted the results.

Uranium, the heaviest naturally occurring element on earth, should have become something heavier when hit by the smaller neutron, and this is how Fermi's team chose to see things --doggedly driven by the allure of alchemy, as many were since the discovery of the handy neutron only a couple of years earlier.

For the next five years, scientific teams around the world (including Meitner's in Germany, working with Otto Flahn and Fritz Strassman), continued to puzzle over the strange results: the products of Fermi's experiment just didn't seem to follow the pattern--they seemed, by their chemistry, to be elements with about half the mass of uranium.

This bothered Lise Meitner especially, and after she was forced to flee Germany in the summer of 1938, she maintained contact with Otto Flahn and continued to urge them to solve the problem.

Finally, on Christmas day in 1938, Meitner and Otto Frisch took a famous walk in the snow in Sweden and solved the mystery--the "strange results" were actually the smaller products of uranium splitting, a process that Frisch coined "fission" (borrowing the term from the process of cellular division in biology). The culmination of this thought process was a letter to "Nature", published on February 11, 1939, that outlined the fission process to the world for the first time, and included a reasonably accurate estimation of the massive and unprecedented amount of energy released (millions of times more energy than any chemical reaction witnessed to that date).

Understandably, this discovery sent shockwaves through the foundations of science, and teams around the world scrambled to learn as much as they could about this new phenomenon. Meitner's brilliant insight led directly to nuclear power, nuclear medicine, industrial radioisotopes, and of course--nuclear weapons (for which Meitner always felt sadness, although she personally played no further role in their development). Despite her pivotal role, Lise Meitner was passed over by the Nobel committee, which awarded the 1944 award for the discovery of fission solely to her colleague Otto Hahn back in Nazi Germany--a dark moment in Nobel history, during a dark moment in human history.

There are a few Canadian connections here: In Ottawa a young NRC physicist named George Laurence eagerly followed the developing story on fission and decided to try a few experiments at the NRC laboratories at 100 Sussex Drive. It was here, in the years 1940-1941, that Laurence built one of the world's first nuclear reactors with graphite and uranium (predating Fermi's team in Chicago); however, lack of purer material, not to mention a more strongly funded project, prevented Laurence from achieving the world's first self-sustained chain reaction (this triumph was left to Fermi in December 1942). George Laurence went on to have leading roles at both the nuclear crown corporation. Atomic Energy of Canada Limited (AECL), and the nuclear regulator, Atomic Energy Control Board (now CNSC).

Meanwhile, in wartime Paris the team of Halban, Joliot-Curie, and Kowarski took another tack in the fission game--exploring the combination of heavy water (a rare form of water) and uranium. Their work led directly to the nuclear program in Canada, culminating in the unique CANDU reactor design that today leads the world in safety and performance (and runs half of Ontario).

In many ways, Lise Meitner and Otto Frisch's brilliant but relatively simple paper in February 1939 marks a sea-change in 20th-century science: the culmination of a "golden" half-century of nuclear science (possibly the greatest period of scientific advancement in human history), and the start of a half-century of rapid development of nuclear technology for the benefit of mankind.

It is noteworthy that the golden era of nuclear science is "bookended" by two remarkable women: Marie Curie, who introduced the world to radioactivity at the turn of the century, and Lise Meitner, who showed how to unlock an unimaginable wealth of energy within the nucleus. Although both women were visionaries it's probably safe to say that neither foresaw the full legacy of their genius: one of the most powerful tools in the fight against cancer, heart disease, and food-borne illness, an almost limitless source of heat and electricity, smoke detectors keeping watch while we sleep, automated probes exploring the furthest planets, and numerous other industrial, medical, and scientific applications.

Until the discovery of fission, nuclear radioactivity, as astutely foretold by Lord Rutherford himself (the great nuclear guru, who unfortunately passed away just two years before fission's arrival), seemed forever doomed to the status of scientific curiosity. Fission let us control the nucleus, and direct its energy to do our bidding.

And, as has doubtlessly been the case on a number of occasions in human history, it took a quiet walk in the snow to tease out the secret.

Jeremy Whitlock is a scientist at AECL Chalk River Laboratories, and currently manager of Non-Proliferation and Safeguards. He is also a writer and speaker on nuclear issues, including The Canadian Nuclear FAQ (www. nuclearfaq.ca), a website of frequently-asked questions (FAQs). Dr. Whitlock lives with his wife and three children in Deep River, Ontario, and feels that canoes are the closest humans have come to inventing a perfect machine.
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Author:Whitlock, Jeremy
Publication:Humanist Perspectives
Geographic Code:4EUGE
Date:Mar 22, 2014
Words:938
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