WORK ON THE ATOM

Grey River Argus, 8 September 1939, Page 8

WORK ON THE ATOM

Problem of Nucleus ACTION UNDER BOMBARDMENT. NEW ELECTRON FOUND. As Cambridge has become very famous as a home of research on the 1 nature of atoms and matter, it was | natural that the physical discussions i at his year’s meeting of 4he British Association should start with a symposium of the physics of the nuceli of i is, writes the scientific correspondent of the “Manchester Guardian.” v .<vd recently there could have been only one possible opener of such a discussion, but now there is no Lord Rutherford to act as a guide in these matters as by a natural right, but, fortunately, his great pupil, collaborator, and friend, Niels Bohr, was able to oe present, and he was supported by Cockroft, Dee, and Feather in a ../view or the newest knowledge concerning the fundamental constitut.on of matter. Bohr said that Rutherford had changed the whole outlook in physics and natural philosophy, but ne would not describe this, for he would follow Rutherford’s own spirit and look forward rather than to the past. He explained that the newest discoveries were concerned with properties of matter quite different from what was familiar up to even ten years ago. A , The structure of the atom as established by Rutherford thirty years ago consisted of a very small, heavy, and highly charged nucleus surrounded by whirling electrons at relatively very great distances. The atom was a very spacious open structure consisting of whirling particles which could be conceived as points.

STUDY OF THE NUCLEUS. The enormous advances which followed this simple idea were due to the fortunate circumstances that as lhe sizes of the constituent particles were so small they could be neglected. For over a quarter of a century physicists were able to reap the harvest of this fortunate fact, but when they arrived at such detailed knowledge of atoms that the internal strucure of the constituent particles themselves could no longer be neglected. It was known that the nucleus was very small but relatively heavy. “ The matter of which it is composed must, therefore, unlike that of an atom as a whole, be extremely compact. Now the experiments on the disintegration of atoms had shown that the nuclei were not indestructible but that various particles could be obtained from them. The nucleus itself must have some sort of structure and the particles which composed it must be Very close together. Thus the essential difference between the atom and its nucleus is that the constituent particles of the atom are very far apart, while those of the nucleus are very cldst together. . It has been ascertained that'" the mutual forces of interaction between are quite different from those which act when the particles are far apart. This can be deduced from whaj/happens when particles are shot at each other by radio-active substances ol* by high-voltage machinery. Thus the nucleus cannot be expected to behave like whole atoms when it is bombarded and disintegrated by atomic projectiles. EFFECT OF THE NEUTRON./ It has been found, as was foreseen that the neutron would be an extrai ordinarily effective disintegrator of [atoms, it has no electric chargd and is therefore not repelled by the electric charge on the nucleus. But the neutron disintegrates the nucleus too quickly. Calculation shows that if it is shot at the nucleus it would usua J l Y be inside the small nuclear space far too short a time to be able to exert any effective ' disintegrating action, bomehow the impinging particle must be held and delayed inside the nucleus in order to have the opportunity o exert its effect. . Bohr has been able to explain this phenomenon in* a general way by means of his billiard-ball theory of, disintegration. If the nucleus- consists of several particles close together the impinging particle will cannon among them and share its energy, and not have enough to escape again until it or some other particle is thrown out by gaining much speed after a series of heavy bumps. Bohr illustrated the idea by a simple mechanical model consisting of a low-rimmed bowl into which steel ball bearings could be rolled.- If there were no halls inside the bowl then the impm.q- i ing ball from the outside passed, right 1

■ through, but if there were some balls inside they collected the energy of the impinging ball and shared it among them. COLOSSAL HEAT. Thus the nucleus is to be conceived as a gas consisting of colliding particles rather than as a piece of solid. When this nuclear gas is hit by an impingl ng particle in a disintegration its. constituents bump each other so violently that the temperature goes up | enormously. It may be calculated I that it goes up to about forty thou'sand million degrees centigrade. The I disintegration occurs during the pro- { cess of cooling. The nucleus loses its ' tremendous heat by emitting particles and rays. Thus it disintegrates by a ■ process analogous to evaporation. As 1 boiling water disappears or disinte- ‘ grates during evaporation through ‘ the shooting into the air of the par- ’ tides of water, so the nucleus evapor- ‘ ates by emitting electrons. Physicists have tried to work out ‘ the nature of the forces holding the 1 particles in the nucleus together. ‘ There is evidence that the nucleus 1 conjains protons and neutrons and that the proton might be transformed 1 into a neutron with the emission of a ’ pair of electrons and another particle, 1 the neutrino, but it is difficult to con- ■ ceive how the forces between these 1 particles could be of the right So the Japanese physicist Yukawa ' suggested in 1935 that still another 5 electron, a heavy electron, might exist. This heavy electron has recently in a 1 most astonishing way been found in connection with cosmic rays, and is ! now named the Yukon.

results of recent work. Borthe and Dee dealt with the new experimental data which confirm Bohr’s general ideas . Dee is. using the powerful new high-voltage apparatus which has recently been installed m the Cavendish Laboratory through the resources provided by Lord Austm. He showed how such apparatus is becoming accurate enough to provide a spectroscopy, or exact arialysis of the particles and rays emitted by dismtegratin0 * nuclei. Cockcroft described the new cyclotron which has just been installed in the Cavendish Laboratory under hrs direction. This whirls Particles round and round a magnetic field until they receive vast speeds or energies. in„ circular or spiral tracks of the particles,' which are spasmodically acceieated as they travel round the space between the poles of a 50-ton become about 100 yards tong, particles then have many volts energy, but they are not always easy t 0 find. Cockcroft mentioned that his able colleagues had recently lost the beam for several days as they had forgotten for the moment in which direction the magnetic for from the North Pole of a magnet acts, a mistake for which the schoolboy might fail in his examination. He said that artificial s® urce f s r radiations as powerful as those from radium should before long be avaff able in physics laboratories but he did not expect that these would be cheap cr than radium, as the apparatus needed to produce them was voy ex pensive. The new paratuses in the world’s aboratones had already revealed nearly 40 ° w h ic h tvnes of radio-active atoms .whicn should be of fundamental value m biological, medical, and physical research.