Nuclear weapons When describing the Magnox nuclear reactor we explained, on page 81, what is meant by a chain reaction and how it occurs when a mixture of uranium-235 and graphite moderator reaches a critical size. We also explained how the speed of this reaction is safely controlled by the use of boron rods which may be raised …
Nuclear fission The examples of neutron capture just described are concerned with the disintegration of nuclei into two parts of unequal size. In 1939, Hahn and Strassman investigated the action of neutrons on uranium-235 and found that it was split into two roughly-ecuct pieces, one of which proved to be barium and the other krypton. Otto Frisch coined the …
Disintegration by neutrons The discovery of the neutron placed a very important atom-splitting missile at the disposal of physicists. Apart from a-particles, only two controllable particles had been available for the bombardment of nuclei, namely, the proton and deuteron (heavy hydrogen nucleus). The positive charge on both of these particles enablesthem to be speeded up to high energies …
The discovery of the neutron The neutron, which we have already described as one of the nucleons or constituent particles of which the nuclei of atoms are composed, was discovered by James Chadwick in 1933. The story behind it really started in 1930, when two German physicists, W. Bothe and H. Becker, found that when beryllium and certain …
The synchrotron At present, research in particle physics is mostly carried out by the use of proton synchrotrons. In these, protons are accelerated by an alternating electric field and guided by a powerful magnetic field at right angles to it. By this means the particles are accelerated along a circular path from which they may be extracted by …
The linear accelerator Another type of accelerator is shown in Fig. 47.9. It is called a linear accelerator and consists of a series of co-axial tubes connected alternately as shown in Fig. 47.10 and given an alternating potential difference from a very high frequency a.c. source. A narrow beam of particles is injected into the tubes from a …
The Van de Graaff particle accelerator About the same time that Cockcroft and Walton were building their proton accelerator at Cambridge, a physicist in America, named Van de Graaff, was developing an accelerator of a different kind. This one has an electrostatic generator which employs point action and the principle that the charge on a hollow conductor resides on …
Equivalence of mass and energy We have already referred on page 82 to Einstein’s theory of the equivalence of mass and energy. In 1905 he had shown that the relationship between mass and energy is given by the equation, Apart from its importance as the first completely man-controlled splitting of the atom, Cockcroft and Walton’s experiment also provided …
Cockcroft and Walton’s experiment By the end of the 1920s the use of o-particles for bringing about nuclear disintegration had been studied intensively, and the need was felt for more powerful atomsmashing missiles. two research physicists at the Cavendish Laboratory, John Cockcroft and ErnestWalton, conceived the idea of accelerating protons in a powerful electric field and using these …
Cloud chamber studies Supporting evidence regarding the nature of the artificial disintegration was obtained in 1925 by Prof. P. M. S. Blackett, who became President of the Royal Society in 1965. Blackett shot ex-particles into a cloud chamber containing various gases and was able to study ordinary collision processes as well as disintegration. Fig. 46.9 illustrates the common straight-line …