Some recent (1924) experiments of the French scientist, Dr. Albert Nodon, seem to afford the actual proof of Le Bon’s a priori conclusions. In the presence of a number of noted scientists, Dr. Nodon exhibited three photographic plates on which were unmistakable light impressions, which, he claimed, were caused by the rays emitted by a radioactive mineral, an insect, and a green leaf, which had been placed on the emulsion side of the plates in a dark-room.
A similar experiment, in which a dead insect and a dead leaf were used, resulted in no ray impressions on the plates. Dr. Nodon offered as his conclusion that radioactivity is an inevitable accompaniment of living processes, and stated that the strength of photographic impressions produced in experiments such as his are an accurate measure of vitality (see Popular Science Monthly, October, 1924).
Radium is probably present in all the planets and stars. Some time ago the Astronomer Royal of England, Dr. F. W. Dyson, demonstrated the existence of radium and of radium emanation in the sun’s chromosphere (the ocean of incandescent hydrogen gas surrounding the photosphere, or actual surface of the sun).
CHAPTER II
EVERYDAY USES OF RADIUM
During the World War large quantities of radium were employed by the Allies for night compasses, luminous dials on airplanes, gun-sights, etc. In times of peace it is used on pendants for locating electric lights and switches in the dark, key-holes, fire-extinguishers, poison bottles, emergency call-bells, and in many other ways. For example, some mining corporations use signs in their mines made luminous in the dark by phosphorescent paint made from radioactive substances. These luminous signs are not affected by atmospheric conditions.
Yet for all these uses, including “radium watches” and clocks, not more than half an ounce of radium has been used since its discovery in 1898. A few millionth parts of a gram of radium, in the form of radioactive barium sulphate, a large portion of phosphorescent zinc sulphide (crystallized zinc), mixed with varnish and some adhesive substance, give enough material to illuminate 40 or 50 watches. One gram of radium (= 16 grains) combined with 20,000 grams of secret process phosphorescent zinc sulphide is sufficient to make 667,000 watches luminous for many years. The factories of this country are now turning out about four million radium watches annually.
Unless a special preparation—known only to the manufacturer—is used, the luminosity of the material gradually disappears, owing to the destruction of the zinc sulphide crystals by the powerful rays constantly bombarding them, producing flashes at the rate of 200,000 a second. The radium itself does not glow, nor does it deteriorate in power.
If we examine a luminous dial through a magnifying glass, after the eyes have been in total darkness for a few minutes, tiny flashes of light may be seen. These are caused by the explosion of hundreds of millions of radium atoms. The more radium there is in the paint, the greater the number of flashes per second, and the more durable the luminosity. Since every flash means a blow upon a crystal of zinc sulphide, the crystals gradually break under the strain. In this process helium is released from the disintegrating radium atoms.
Mr. M. A. Henry (Scientific American, April 2, 1921) points out that the problem of the chemist “is to produce a phophorescent substance which will stand up longest under the terrific bombardment of the radium rays and which, at the same time, will give off the most light. Such progress is being made in this direction that today [1921] only about one-twentieth the amount of radium used four years ago [1917] is needed in the making of luminous material. And the chemist insists that he has only scratched the surface of possibilities in this direction and that even better results can be attained. At present the life of the zinc crystals is from 15 to 20 years, although the radium lasts for centuries.
“This life will be much longer if the instrument to which it is applied is kept away from the light most of the time. The crystals, already stressed by the radium rays, have an additional strain imposed by the light and this hastens the process of disintegration. Strong sunlight, especially at the seashore where the presence of much ozone in the air intensifies the ultra-violet rays, has a very destructive effect on luminous material. For this reason the manufacturers of this delicate substance usually guarantee it for about half its normal life, or ten years.”