COSMIC RAYS

Hawke's Bay Tribune, Volume XXIII, Issue 78, 14 March 1933, Page 7

COSMIC RAYS

LIGHT ON THEIR ORIGIN A NEW APPARATUS. PHOTOGRAPHY USED, The exact nature of cosmic, rays is not yet known. It is not even absolutely certain whether they are cosmic, originating not in the earth’s atmosphere but in outer space. The true nature of these rays will, however, be elucidated more quickly by the re markable invention made by Mr. P. M. S. Blackett and Mr. G. Occhialini, of the Cavendish Laboratory at Cambridge, who have just described in “Nature” the apparatus they have devised for making cosmic rays, or the effects of cosmic rays, photograph themselves, says the “Manchester Guardian. ’ ’ Bkobelzyn three years ago showed that particles moving with enormous energy may be detected iu the earth’s atmosphere. Whether these particles are themselves cosmic rays or whether they are produced by cosmic rays is not yet decided. But the invention of a machine which automatically goes oft' when one of these swift particles enters it means that a great increase in efficiency 7 in the observations of cosmic ray effects has now been obtained. These swift particles discharge the apparatus about once iu every two minutes. Hitherto, they, or their tracks, were photographed by taking photographs continuously. Thus tnousands of photographs had to be taken in order to get a few suitable tracks. This neat and ingenious apparatus, which photographs only when a particle goes through it. is typical of the Cavendish experimental style. Mr. Blackett takes pairs of photographs of each track so that its direction in space may be exactly determined. MANY VOLTS. Of a hundred such pairs of photographs he found 59 showed tracks of particles, which, if they were electrons, would exceed 500,000,000 volts. In connection with this, it is interesting to remark that Heisenberg has been able to explain many of the properties of cosmic rays on the assumption that they are electrons travelling under a pressure of about 1,000,000,000 volts. Besides the 59 pairs of photographs showing the high-speed tracks, 17 showed multiple tracks and 24 showed no tracks. Thus Mr. Blackett’s machine appears to be working with an efficiency of no less than 76 per cent. It is remarkable that at the first attempt his apparatus should catch the effects of cosmic rays so efficiently. The energy of the flying particles is determined from the deviation they suffer in a magnetic field.

The research in cosmic rays is now being pursued by many workers throughout the world. The existence of a penetrating radiation was suspected from experiments made by McLennan and Rutherford in 1905. About 1910 Kilhorster showed that the penetrating radiation increased in intensity higher up in the atmosphere. This seemed to prove that it entered the earth's atmosphere from outside, and the notion of rays from cosmic space arose. AID TO RESEARCH. The study of the nature of the rays received great impetus from the researches of Millikan made about 1920. His spectacular experiments with highflying balloons carrying recording instruments and his study of the absorption of the rays by the water of lakes, combined with his decided views concerning the nature of the rays, created immense interest in them. Millikan believes the cosmic rays are waves emitted at the birth or formation of complicated atoms out of simple atoms. He believes the rays come to the earth with equal intensity in all directions, and that they do not vary between day and night. These findings would appear to show that the rays are independent of the latitude at which they arrive on the earth. If this were certain they could not well be charged particles, or would have to possess immense energy not to be deflected by the earth’s magnetic field as they approach. If they were charged particles they would presumably collect at the earth’s magnetic poles. Recently A. H. Compton and. others have obtained evidence that the rays do vary with latitude, which differs from Millikan’s finding. Hoffman has evidence that the intensity of the rays varies more during the day than at night. Hess considers that one-half per cent, of the cosmic rays observed on the earth come from the sun. If his interpretation of experimental data is correct, the cosmic rays arise not in cosmic space but in the surface of the sun and other stars. VARYING INTENSITY. Gorlin believes his own observations suggest that the intensity of the rays varies during the day and night in a way which shows they come from, particular parts of space, particularly nebulae, perhaps. Nodon thinks that part of the rays come from the sun and part not from the sun. Bennett, Steams, and Cameron find the rays are about 1 per cent, more intense between 8 a.m. and 4 p.m. than between 8 p.m. and 4 a.m. They conclude that they originate in the space near the sun, from a region about twice the diameter of the distant planet Pluto.

The cosmic ray researches are in a most interesting condition. It is uncertain yet whether they are waves or particles, electrons or neutrons, whether they come partly from the sun or from outer space. But a large group of the best physicists in. the world are now concentrating on them, from Koihorster and Millikan, who did most, of the early experimental work, to Rossi, Skobelzyn, Compton, and others. No less a person than Heisenberg has discussed the theory of the rays, Professor Bohr’s colleagues at Copenhagen have made some excellent experiments, and now the famous investigators of the Cavendish Laboratory are in the front line of this fascinating research, started in paif. by one of them twenty-nine years ago.