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A previous dismissal of fission because of inaccurate measurements


Experiments into the fission of uranium
Edward Teller Scientist
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Let me perhaps explain, lest the point be lost, why you get so many radioactivities. The heavier an element is, the more the repulsion between the positive charges, the protons betters. The nucleus is actually composed of protons and neutrons approximately equal in number for the light elements, but as elements get heavier and heavier, the fraction of neutrons gets greater and greater. And the charge on a nucleus makes the nucleus less and less stable, so a little additional energy can cause the splitting. But the parts into which uranium splits, which now is a lighter nucleus, with fewer neutrons and protons, have a neutron to proton ratio which is high as is the fashion for very heavy nuclei. And radioactivity consists in the transformation of neutrons into protons or vice versa. And the fission of uranium leads to individual particles which for size are over rich in neutrons and therefore will give a lot of decays. In addition to the point that the splitting can be into unequal parts or into equal parts and hence the great amount of various radioactivites. Now, this point has been considered carefully in Germany, in the Kaiser Wilhelm Institute. And it was considered, to a very great extent, of looking at the radioactivities which are created, chemically separating out some of these radioactivities and finding that, for instance, one of them was indubitably iodine, clearly less heavy than uranium. That was discovered by Hahn and Strassman in Germany and they wrote to their friends, their Jewish friend, Lise Meitner, who had to leave Germany and was in Copenhagen, and Lise Meitner, together with her nephew, Frisch, actually planned an experiment in which these fragments, the higher the ionizing particles, could be seen. In the usual experiments of Fermi, a neutron was attached to a nucleus and then sent out one lowly beta decay. In this case, the neutron absorption led to two highly charged, fast moving particles which could cause strong ionization in Geiger counters, which I think I have already told you about in connection with the experiment on the unfortunate cat. Meitner and Frisch made the experiment and actually have seen these fragments. They did that after Bohr has sailed for the United States and by the time of his arrival in the United States he heard of the successful experiment. It was a real succe- sensation. And characteristically, and in a way, surprisingly, it was repeated in a short time in several American laboratories.

The late Hungarian-American physicist Edward Teller helped to develop the atomic bomb and provided the theoretical framework for the hydrogen bomb. During his long and sometimes controversial career he was a staunch advocate of nuclear power and also of a strong defence policy, calling for the development of advanced thermonuclear weapons.

Listeners: John H. Nuckolls

John H. Nuckolls was Director of the Lawrence Livermore National Laboratory from 1988 to 1994. He joined the Laboratory in 1955, 3 years after its establishment, with a masters degree in physics from Columbia. He rose to become the Laboratory's Associate Director for Physics before his appointment as Director in 1988.

Nuckolls, a laser fusion and nuclear weapons physicist, helped pioneer the use of computers to understand and simulate physics phenomena at extremes of temperature, density and short time scales. He is internationally recognised for his work in the development and control of nuclear explosions and as a pioneer in the development of laser fusion.

Duration: 5 minutes, 17 seconds

Date story recorded: June 1996

Date story went live: 24 January 2008