Fission: a story of two unequal parts

There is a legend about the peripatetic and indefatigable Hungarian scientist Leo Szilard, who substantially contributed both to the production of the atom bomb and to the efforts to control it. During a stay in London in 1933, he was walking in his favourite Bloomsbury when a thought struck him: when some atomic nuclei are hit by neutrons, more neutrons may be emitted, making possible a chain reaction with the release of a vast amount of energy, that could be used for peaceful and military purposes. Szilard prepared a plan for the systematic study of all elements, but he failed to find financial backing for it, and the project was abandoned. Later, he claimed, jokingly, that he should have received the Nobel peace prize for not pursuing the idea.

What might have been the consequences of an earlier discovery of fission? Would it have led - as implied by Szilard - to Germany, under Hitler, being the first to develop the atom bomb and thus gain world domination? Or, perhaps, would there have been agreement among world scientists to develop the peaceful applications of nuclear energy, but refrain from work on the military aspects? While such "what-would-have-happened-if" questions are idle speculation, some of the actual happenings are, amazingly, still disputed. What worried many was why the Nobel prize for a major discovery in physics was awarded to a chemist who had no idea of the nature of the discovery?

Fifty years after the event, the quandary has again been brought to the surface by the publication of the biography of Lise Meitner by Ruth Lewin Sime. Meitner is portrayed as the co-discoverer of fission, who should thus have shared the prize with Otto Hahn. In the blurb of the book, Hahn and other members of the German scientific establishment are accused of efforts "to obliterate Meitner's pre-eminence in 20th-century physics". This is not put so blatantly in the text itself, but considerable space is devoted in the book to the circumstances of the award of the Nobel prize, with strong hints of a conspiracy, involving a Swedish Nobel laureate, to deprive Meitner of a share in the prize. While one can understand (though not excuse) the endeavour of biographers to present their heroes in the best possible light, it is sad that in the effort to give the maximum credit to Meitner, Sime has marginalised the role of the real discoverer of fission.

As a history of the life of Meitner the book merits strong commendation. Sime has obviously put in an enormous effort in researching the subject. The narrative makes fascinating reading, although for the lay person the account of scientific experiments may be too detailed. and often lack a critical evaluation of their significance.

What emerges is a vivid portrait of a scientist, who throughout her life had to combat prejudices and discrimination against gender and, as a Jew, against race. But, with strong determination, she reached the top rank of German physics in the period between the two world wars.

Long before Nazism perverted German science, she had to overcome the bias against women's right to education, prevalent in the Austrian and German empires at the turn of the 20th century. Against overwhelming odds, she managed to get herself educated in her native Vienna, where she received a doctorate in physics in 1906, at the age of .

After a short spell of research in the new field of radioactivity, Meitner went to Berlin, to supplement her studies. It was meant to be a short visit but it lasted for more than 30 years, practically the whole of her scientific career. One of the first scientists she met there was her contemporary, Otto Hahn, a graduate in chemistry, who had just then begun research work in radioactivity. Thus started a collaboration that lasted for the remainder of her active life in research, and a friendship that was very close for many years but later turned into animosity. At the time they met the nature of the new radioactive substances was being established by chemical separation and physical identification of emitted radiation. The collaboration between a physicist and a chemist provided the ideal combination for fruitful research.

Even in Berlin life was difficult for a woman scientist. The director of the Chemistry Institute forbade entry to women. As a compromise, Meitner was allowed to work in a basement, with a separate entrance; to use a toilet she had to walk some distance to a restaurant. For a number of years she received no remuneration, and until the age of 34 she was dependent financially on an family allowance. Gradually, however, her scientific achievements received due recognition. She was awarded the appropriate academic titles, and eventually put in charge of the physics department within the Kaiser Wilhelm Institute for Chemistry in Berlin-Dahlem.

However, the onset of Nazism soon poisoned the atmosphere in the German scientific community. Having retained Austrian citizenship, Meitner was not subject to the draconian anti-Jewish laws and she retained her post, but her life was made increasingly unbearable by many of her co-workers. Eventually, by the Anschluss of Austria in 1938, she became formally a German citizen, and, her position being untenable, she fled Germany in July 1938. Shortly afterwards, the fission saga began.

The last few years before leaving Berlin was a period of intensive study, carried out jointly with Hahn and another chemist, Fritz Strassman, on the identification of the radioactive substances arising from the bombardment of uranium with neutrons. From experience with other nuclear reactions, one would expect the products to be elements near uranium, some of them transuranic. However, there were too many of these products and their chemistry was puzzling. Meitner tried to explain this by nuclear isomerism, ie, formation of nuclides in different energy states, leading to different radioactive substances. Their work in Berlin was largely based on this concept.

In December 1938, following results obtained in Paris, Hahn and Strassman changed their approach, and soon established beyond any doubt that barium (an element with about half the atomic number of uranium) was among the products of the bombardment of uranium. They were unable to interpret this finding and, just before Christmas, they wrote to Meitner, then in Sweden, asking her advice.

It so happened that her nephew, Otto Robert Frisch, a 34-year-old Austrian physicist, who at that time worked in Bohr's institute in Copenhagen, came to spend Christmas with her. It occurred to them that here was a new type of nuclear reaction, the splitting of the nucleus into two nearly equal parts; a process which, by analogy with the division of biological cells, Frisch named fission. From an analysis of the physics of the process they deduced that a relatively very large amount of energy should be released at fission. In a simple experiment soon afterwards, Frisch actually observed this energy release.

In his memoirs, What Little I Remember, Frisch described the reaction of Danish physicist Niels Bohr when he told him about the fission concept. Bohr exclaimed: "Oh what idiots we all have been! Oh but this is wonderful!"

Even before Meitner and Frisch's paper was published in Nature, in February 1939, the news reached scientists, provoking a flurry of activities. Soon, experiments were carried out showing the emission of several neutrons at fission, opening the way to a nuclear chain reaction, with its awesome potential. Before the end of 1942, the first nuclear reactor became operational, and less than three years later two atom bombs destroyed Hiroshima and Nagasaki. The nuclear age began.

Three months after Hiroshima, the Nobel prize for chemistry was awarded to Hahn "for his discovery of the fission of heavy nuclei".

The Nobel award to Hahn alone raised many eyebrows. For one thing, the work was done jointly with Strassman, who should have shared the award. The question of Meitner's part in it is more complex. Hahn claimed later that Meitner was responsible for the delay in making the discovery, and there is something in that.

She was known for sticking obstinately to her ideas. (Years earlier she had been involved in a fierce controversy with the British physicist Charles Ellis about the nature of beta decay, and she held on to her views despite much evidence that she was wrong.) Her insistence on the isomerism concept may have kept Hahn and Strassman on the wrong track. But even so, considering her leading role during the many years of their collaboration, she should have had a share in the Nobel prize.

There is, however, a more general question: should the Nobel prize for the discovery of fission be given in chemistry and not in physics? What Hahn and Strassman did was to prove that barium is produced when uranium is hit by neutrons. For this they probably deserved a Nobel prize in chemistry. But they had no inkling about fission, and they would never have cottoned on to the idea of it. Fission is a physical process and it is unbelievable that the discovery which has led to such portentous consequences has never been recognised by a Nobel prize in physics. And the physicists who should have received this are Frisch and Meitner.

Having said this, I should state my opinion that of these two, it is Frisch who is the real discoverer of fission. In his account of the historic meeting with his aunt, Frisch presents it as a joint effort; this is in accord with his generous nature. But I have no doubt that the idea came from him. This is based on my analysis of their two personalities. Meitner was a good scientist - thorough, persevering, but with not much intuition; she lacked that something extra which makes the difference between an ordinary scientist and a genius. Frisch was a genius. This is evident from his whole life, from the many important contributions he made in the follow-up to the discovery of fission, from the numerous brilliant ideas he had, and ingenious experiments he devised.

Meitner received many other honours. She took a triumphant tour of the United States; she was awarded the prestigious Enrico Fermi prize; she has an element (number 109, meitnerium) named after her. By contrast, Frisch is nearly forgotten, except by the rapidly decreasing circle of his friends and scientific colleagues. It is high time that a historian takes up the job of writing the life of that remarkable man.

Joseph Rotblat is president, Pugwash Conferences on Science and World Affairs, and winner of the 1995 Nobel peace prize.