16 February 2012

The method is refined

Part 3 - The method is refined:

After his six-year stay in Copenhagen in the early 1920s, George de Hevesy is offered a job in Germany. However, it is not long before it becomes too dangerous for the Jewish Hevesy. Niels Bohr invites him back to the Institute for Theoretical Physics at the University of Copenhagen to continue research on the tracer technique.

In 1927, George de Hevesy was appointed professor in Freiburg am Breisgau, where he worked until 1934, when he had to leave the Third Reich due to his Jewish background.

Back to Copenhagen

Niels Bohr invited him to Copenhagen again, where he remained and conducted research for nearly 10 years during the period 1935-1943.

It was during his stay at the Niels Bohr Institute that Hevesy refined the tracer method with Ole Chievitz, August Krogh and of course Niels Bohr.

Niels Bohr and George de Hevesy — To the left is Niels Bohr and to the right is George de Hevesy.

By that time, it became possible to artificially produce useful amounts of radioactive substances, including phosphorus-32 and this meant that the tracer principle could be used much more broadly in biology.

Incredibly primitive instruments

George de Hevesy also got his own assistant, the young German physicist Hilde Levi, who like Hevesy had fled the Nazi regime in Germany. Hilde Levi built Geiger counters based on simple amplifier principles and used the telephone headquarters telecommunications system to record the number of beta particles.

Hevesy wearing a suit in the laboratory. He was not a good experimental chemist and was often a patient in the emergency room at Rigshospitalet, which neighbours Blegdamsvej.

To begin with, they had a neutron source with a mix of radon gas and beryllium powder that could deliver very small amounts of radioactivity. Later, they could produce radioactive phosphorus by bombarding sulphur with neutrons.

These were extremely primitive instruments and today it impressive to think about the revolutionary discoveries the little research group made.

It is quite remarkable that they achieved so much starting from the limited experimental opportunities available at the time.

The first experiment in which radioactive indicators were used for physiological experiments, was an experiment in which phosphorus-32 was injected into rats and tracer was then absorbed into the skeletal system.

Studies in rats showed bones like organs

The article was published in a “letter to the editor”, in Nature. It was submitted in September 1935 with Hevesy and Chievitz as the authors.

After injection into the bloodstream, you could show, using counting setups, that phosphorus-32 was absorbed into the bones and expelled again.

Hevesy’s conclusion of the study was that bone formation is a dynamic process where the bone continuously absorbs phosphorous atoms, loses them again and replaces them with other phosphorous atoms.

It was revolutionary that using this method, you could for the first time show that the bones are a living organ and not just a skeletal frame inside the body.

Short distance from thought to action

The experiments were performed with the help of Ole Chievitz, Bohr’s old classmate who was a surgeon and head of the surgical department at Finsen Institute. Chievitz carried the experimental studies and the animal studies were later expanded to include experiments on rabbits and cats.

It must have taken place very quickly and it a short distance from thought to action. Just half a year after Hevesy arrived in Copenhagen, he had introduced the technique that he had dreamed about for almost 20 years.

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Hilde Levi

Hilde Bertha Levi (1909 – 2003) had a doctorate in chemistry and physics and was an assistant to George de Hevesy during his stay in Copenhagen,

Hilde Levi, who was of Jewish descent, received a doctorate in chemistry and physics at the University of Berlin in 1934. The Nazi dominance in Germany meant she had no future there and through the International Federation of University Women she instead became attached to the Niels Bohr Institute for Theoretical Physics, where she worked as an assistant for Georg de Hevesy.

In 1943, Hilde Levi had to flee to Sweden, where she worked at the Wenner-Gren Institute in Sweden for the rest of the war. When Niels Bohr phased out biological research after the war, Hilde Levi received an offer to continue at August Krogh’s Zoophysiological Laboratory in Copenhagen – she worked here until she retired in 1979.

In the late 1940s, she took the initiative to build an apparatus for carbon-14 dating, which – as the first of its kind in Europe – became operational in 1951 and was used for dating Grauballe Man.

From 1952 to 1970, Hilde Levi was a consultant in connection with the Danish Health and Medicines Authority’s efforts to develop legislation for radiation protection.