ATOMIC FORCES

Otago Daily Times, Issue 26214, 26 July 1946, Page 4

ATOMIC FORCES

CONTROL OF ENERGY COLOSSAL POSSIBILITIES A BOON TO CIVILISATION “There is great need that everyone should realise the terrible catastrophe which would result from another war. On the other hand, the release of atomic energy under control can become one of the greatest boons to civilisation. We are at the beginning of the), atomic age. It can be made a time e ’of disaster or of great progress.” In those words, Dr R. Jack, professor of physics at the University of Otago, concluded an address at Mosgiel last night under the auspices of the W.E.A. Professor Jack discussed atomic energy in some detail and traced the history of the artificial splitting-up of atoms since Rutherford shot alpfya particles (the nucleus of a helium atom) into nitrogen atoms and produced hydrogen and oxygen atoms in 1919. The Mayor of Mosgiel, Mr W. P. Hartstonge, was in the chair. The fundamental law about the release of atomic energy was put forward by Einstein in 1905, he said. From that law, it was easily deduced that if one gram of matter could be annihilated, the released energy would represent 21,000,000,000.000 calories, or the energy to keep one 100 watt lamp burning for 250,000,000 hours or- to give 33,000 horse-power for 42 days. No Exaggeration

” It can therefore be seen,” he continued, “ that there is no exaggeration in the statement that if one .drop of oil were annihilated, the energy obtained could drive the* Queen Mary across the Atlantic and that one cup of water would suffice to take the Queen Elizabeth many times round the world. In the atomic bomb, one-thou-sandth of its mass is annihilated, and therefore it can be understood why its temperature can rise to millions of degrees Centigrade and the pressure of gases formed to millions of atmospheres if the action takes place suddenly. The figures show that of- each pound of uranium used in an atomic bomb, about one-half of a gram is annihilated, and so the energy created is about half of the above figures for each pound of the vital constituent in the bomb.”

To explain the importance of uranium (235), Professor Jack analysed the composition of atopis of water and discussed the components of atoms—protons, neutrons, and electrons. The chemical properties of an atom depended on the numbers of protons and electrons, which were the same in a neutral atom. The protons in any nucleus repelled each other with strong forces, but there were attractive forces between protons and neutrons which were very large at short distances. With large numbers of protons and neutrons within the nucleus, however, the packing became less tight with the result that the heaviest atoms became unstable and charged particles, such as alpha particles containing two protons and two neutrons, were sometimes spontaneously shot out from them at great speeds. Release of Energy

After discussing atomic masses and stresses in technical vein, Professor Jack said that the reduction of mass could also take place in the breaking up of an atom into fragments. The uranium atom in the atomic bomb could be split into a barium and a krypton atom,' but' the protons and neutrons in the nuclei of the last elements were more tightly packed than in the uranium nucleus. The masses of the fragments added together were less than that of the uranium atom. Therefore energy was released and the fragments were shot off at very high speeds. A comparison with the energy released in combustion was that the energy actually released when one atom of Uranium was split up was about 50,000,000 times greater than when an atom of carbon was combined with oxygen in comby'st'ioh; Professor Jack reviewed, research in this subject from Rutherford’s first successes to the discovery in January. 1939, by two Germans, Hahn and Strassmanny, that after the neutron entered the uranium atom an unstable nucleus was formed which split up into fragments, one of which was identified as barium. Since energy would have to be released in the process 'it was immediately recognised by physicists that the discovery was of great importance. The Danish physicist, Bohr, suggested that it was the uranium which was split and the process was called fission. Controlling Reactions .. .Experiments showed that enormous amounts -of energy would be released if only a few pounds of uranium had their atoms split. There remained the difficulty of producing a quick chain of reactions following the initial splitting at one point. It was discovered however, that two or three fast neutrons were shot off as well as the fragments from the uranium atom when it was split. If there were impurities present which absorbed those neutrons or if too many escaped from the surface a chain might not result. If. then, uranium were distributed throughout a large volume and the impurities were kept within limits, a chain was possible. Such a continuously active generator of energy had been called a pile. The more uranium there was in the pile, the quicker was the energy generated. ■ •

It was found that the fast neutrons coming from the uranium (235) were not fast enough to enter the uranium (238), but that they could enter with the help of collision with light atoms such as the carbon in graphite, which for this purpose was called a moderator. When the slow neutrons did enter the uranium (238) nucleus, the atom formed changed after two electrons had been emitted into plutonium," which could be separated chemically. It was also found that that uranium (235) and plutonium allowed both slow and fast neutrons to enter their nuclei. Those atoms then split up with release of energy, and, therefore, either could be used in the atomic bomb. Energy was released in both cases—in the former slowly and with the possibility of control, and in the latter, if only uranium (235) or plutonium were used, explosively. The atomic bomb, Professor Jack concluded, was got by using only uranium (235) or plutonium. As long as the size was kept below a certain value, a chain reaction was not started. If two blocks whose total mass was greater than the minimum to give a chain reaction were suddenly brought together, however, or if controls were suddenly" removed from one large block, then all the atoms might be split in less than one-millionth of a second. Enormous temperatures and gaseous pressures were at once produced. It had been said that the Hiroshima bomb was equal to 20,000 tons of T.N.T. and that a bomb was now ready equal to 20.000,000 tons of T.N.T. ’