The Nobel Prize in Chemistry 1944
Otto Hahn
Presentation Speech by Professor A. Westgren, Chairman of the Nobel Committee for Chemistry of the Royal Swedish Academy of Sciences, on December 10, 1945*
Your Majesty, Your Royal Highnesses, Ladies
and Gentlemen.
When chemical compounds form or decompose, interaction takes
place between the outer parts of the electron shells. In view of
the fact that, up to recent times, chemistry was nearly entirely
concerned with the study of the combining of atoms and their
release from combined units, it can be said that up till recently
it was the science of the peripheral parts of the atom. But today
a new discipline has grown up, that of nuclear chemistry, which
deals with the centre parts of atoms, their nuclei, and which to
judge from its recent achievements, promises to revolutionize
science.
An atomic nucleus is a very small thing. Rutherford found that its diameter is
about ten thousand times smaller than that of the atom, or about
one billionth (10-12) of a centimetre. And yet, by
means of the particles charged with energy of the radioactive
elements, particles which act as projectiles, he succeeded in
detaching small fragments from certain nuclei. The fragments
detached in this way were found to be hydrogen nuclei or protons,
which showed that these atomic nuclei, despite their minute
dimensions, were composite structures made up of protons. Later,
Joliot and his wife Irène
Joliot-Curie studied in greater detail what happens when
different kinds of elements are exposed to radiation by positive
particles rich in energy. Here transmutations of elements may
occur, but the atoms which then form are generally unstable and
break up spontaneously with the emission of different kinds of
elementary particles.
Fermi used the
neutron discovered by Chadwick as a projectile
to obtain nuclear syntheses. The neutron has the same mass as the
proton, but as its name indicates it differs from it through
bearing no charge. Thus it is not repelled by the positive atomic
nuclei and will combine with them more easily than the
projectiles with a positive charge used previously. In this way
Fermi was able to produce a large number of new kinds of
radioactive atoms.
All these researches into nuclear chemistry were concerned with
relatively slight modifications to the mass of the reactive
nuclei. Here it was simply a question of the addition or loss of
different sorts of elementary particles. The reaction processes
discovered by Otto Hahn are of quite a different nature. They
involve the splitting of heavy atomic nuclei into two parts of
more or less equal size.
In collaboration with Lise Meitner, with whom he has worked for
nearly thirty years, Hahn studied from 1936 to 1938 the products
obtained by projecting neutrons on to the heaviest elements,
thorium and uranium. According to Fermi, elements would appear
which would form a continuation of the Periodic Table of the
elements. Hahn and Meitner believed they could confirm this
assumption. But towards the end of 1938, Hahn, in an
investigation carried out with one of his young colleagues, F.
Strassmann, found that one of the products formed through the
reaction of uranium with neutrons and which had been assumed to
be a kind of radium, behaved chemically in fact like barium. In
January 1939 Hahn announced this discovery and expressed in very
discreet terms the daring opinion that on being allied with
neutrons, the atoms of the heaviest elements could split in half
as it were and produce elements belonging to the middle of the
Periodic Table of the elements. After a month he was able to
provide proof of his theory, which was confirmed almost
simultaneously in research carried out in different parts of the
world by scientists using different methods.
Hahn's discovery caused great surprise and evoked lively interest
among the world's scientists. It was immediately made the object
of important theoretical investigations by Lise Meitner and
Frisch, who based their study on the theory of the structure of
atomic nuclei developed by Bohr. These
investigators pointed out that nuclear fission should take place
with an enormous generation of energy, due to the conversion of
matter into energy. Calculations showed that the fragments
produced in this break-up would disperse in all directions with
immense force. Frisch demonstrated this experimentally. In
connection with Joliot's observation that certain products of
nuclear fission break up with the emission of neutrons, this
discovery indicated that it was possible by splitting uranium to
produce a chain reaction generating a very large amount of
energy. The outlook for later research thus became very
promising.
Without equal in the art of the chemical identification of
radioactive elements in minute quantities, Hahn, together with
his colleagues, paved the way for the chemical research which had
to be carried out on the numerous products of the splitting of
heavy atomic nuclei. Fission can be carried out in many ways,
depending on the structure of the reactive nuclei and the energy
of the splitting neutrons. The primary products of fission are
unstable and they gradually decompose, emitting elementary
particles, so that each of them acts as the starting-off point
for more or less long series of different sorts of atoms. So far,
the presence has been demonstrated of about one hundred bodies
which are the direct or indirect products of the processes of the
splitting of matter; these products are connected with 25
elements which lie between selenium and praseodymium in the
Periodic Table of the elements.
The discovery of nuclear fission is very momentous and indeed
dangerous, but even more, it is full of promise. In autumn 1943,
Hahn read a paper to the Swedish Academy of Sciences on his
latest work in nuclear chemistry, and there referred to the
possibility of splitting uranium by means of a chain reaction. In
this process such enormous quantities of energy would be produced
in a short instant that the effect would exceed any explosion
phenomenon so far known. Hahn doubted however whether it was
possible to surmount the technical difficulties involved.
"Providence has not wanted the trees to reach to the sky", he
said, and his hearers guessed from the passion in his voice that
he wished that this conquest of atomic energy had been made at a
much later date. He certainly shuddered at the thought that the
atomic bomb was nearer at hand than the use of atomic energy for
peaceful purposes.
Hahn's work has been inspired throughout by an invincible desire
to solve the problems which he has encountered. Unlike
Prometheus, who gave fire to Man, he has never dreamed of giving
Man control over atomic energy. May humanity weigh deeply the
responsibility which the gift of this discovery has imposed on
it. Then this will be a blessing and a step towards the
improvement of the conditions of human life.
The Academy of Sciences has decided to award to Professor Hahn
the Nobel Prize in Chemistry for the year 1944 in reward for his
discovery of the fission of heavy atomic nuclei. Professor Hahn
has expressed his gratitude, but he has informed us that he is
regrettably unable to attend this ceremony. Therefore the
decision of the Academy cannot at present be implemented by the
awarding of the prize.
Professor A. Tiselius addressed the following words to Professor Otto Hahn, on December 13, 1946
Professor Hahn. At the Nobel ceremony held on 10th December, 1945, you were unfortunately unable to be here in person to receive your Nobel Prize. On that occasion, however, a detailed account of the results of your researches was given by the President of the Nobel Committee for Chemistry. I must therefore restrict myself today to the expression of our great pleasure at the fact that you are able to attend today in person to receive your prize and our congratulations. The discovery of the fission of heavy nuclei has led to consequences of such a nature that all of us, indeed the whole of humanity, look forward with great expectations, but at the same time with great dread, to further developments. I am convinced, Professor, that just as your great discovery has been a result of your far-reaching researches on atomic nuclei, irrespective of any eventual practical applications, the further ardent development of research in this field as a consequence of your work will be of particularly great pleasure to you. With regard to its practical application I am also sure that you share all our hopes that this application will serve in the end as a blessing to mankind.
Professor Otto Hahn. Whilst offering you the sincere congratulations of the Academy, I ask you to receive from the hands of His Majesty the King the Nobel Prize for Chemistry for the year 1944.
From Nobel Lectures, Chemistry 1942-1962, Elsevier Publishing Company, Amsterdam, 1964
* The Nobel Prize in Chemistry 1944 was announced on November 15, 1945.
Copyright © The Nobel Foundation 1944
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