University of San Francisco - USF Don Yearbook (San Francisco, CA)

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26 T1IE I (iS AT I AN spontaneously give out heat and other manifestations of energy which are able to affect a photographic plate; to cause certain substances to fluoresce; and to render the air in their neighborhood a conductor of electricity. These other manifestations of energy are called rays; and from this comes the term radio-activity. Three different kinds of these rays arc distinguished; the alpha, beta, and gamma rays. The alpha rays are responsible for most of the ionization of the air produced by radio-active substances; they can penetrate the air only a few centimeters and are easily stopped by paper. They are connected with the development of the greater part of the heat evolved by such substances. When uninfluenced by external forces they move in straight lines, but under the influence of an electrostatic or a magnetic field, they are slightly bent out of their path and act as though they consisted of a stream of rapidly moving particles charged with positive electricity. The beta rays are more penetrating than the alpha rays and pass readily through paper and even through thin sheets of metal. They are especially active toward a photographic plate. Like the alpha rays they move in a straight line, unless influenced by a magnetic or electrostatic field when they are deflected in the opposite direction from that in which the alphas are turned, and much more strongly. The gamma rays arc characterized by extraordinarily great penetrating power, being able to pass through bodies which will stop the other forms of radiations. No deviation of these rays has been detected in the most powerful magnetic fields it is possible to obtain, and in this respect they arc more nearly allied to the X-rays than to the alpha and beta rays; but in their absorption by different kinds of matter they exhibit an almost complete parallelism to the beta rays. Their effects are insignificant compared with that of the other two types.

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It A DIO-ACT! YE 8VB8TASCES 25 duce the Rout gen Rays. Acting on this idea, he examined some fluorescent compounds of uranium. His method was to place the bare salt above a photographic plate, which was carefully wrapped up in opaque material, and so protected completely from the direct action of light, and to expose the salt to direct sunlight, so as to cause it to fluoresce. While waiting for a sunny day, the apparatus was placed in a dark drawer. Two weeks later M. Bccqucrel decided to test the freshness of the plate by developing it, and to his surprise, a dark spot appeared on it, beneath where the salt had rested. This was proof conclusive that some unsuspected rays had passed through the opaque material, and after delicate tests had been made, it was shown beyond doubt that the new and unsuspected rays were really electrical. It was at this stage that Mine. Curie, one of Professor Becquerers students made such great progress in this new science. She found that radio-activity is an atomic property; that thorium acted like uranium; that pitchblende carrying a given weight of uranium had approximately four times greater activity than any pure uranium salt containing the same weight of uranium. This latter disclosure caused Mine. Curie to conclude that pitchblende contained another clement that was also radio-active, and she proceeded to prove this conclusion. The pitchblende was dissolved, and the various elements in it were precipitated and tested for radio-activity. The principal activity was found to be concentrated in the barium, strontium, and calcium group. After the calcium and strontium had been eliminated, the barium that remained still showed strong activity. This caused Mine. Curie to investigate further, and the element radium was eventually separated by the fractional crystallization of its salts from the corresponding barium salts. This discovery of the new element, radium, was made in 1898. Radio-Active Eli:ments. The elements uranium, thorium, radium, polonium and actinium are radio-active; and by that is meant that they

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BA DIO-ACTIVE SI BSTAXCES 37 Radium. Radium is the only now radio-element that has so far been isolated in the form of pure compounds, or which has been found to give a new spectrum. The quantities of pure radium compounds obtained are excessively small. Only a few tenths of a gram of radium chloride can be extracted from a ton of pitchblende, and this is in the ratio of one part to several millions of the original mineral. On the other hand, the radio-activity of the pure compound is correspondingly increased, and the tiny quantity extracted from a ton of ore retains in concentrated form the greater part of the radio-activity of the original mineral. Weight for weight, the radium compounds arc at least a million times more active than the compounds of uranium and thorium. The atomic weight of radium is 225 which places it in the position of the third heaviest element known, the two heavier being the other radio-elements—thorium 232 and uranium 238. Source and Method of Extraction. Radium is now obtained chiefly from carnotitc, though a small amount is derived from pitchblende. Practically all of the world’s radium until nine years ago, came from deposits in Portugal. The first important radium operations in the United States did not commence until 1912, although a small plant designed to recover uranium from carnotitc ore was erected in Colorado in 1900. The following method of the treatment of radium extraction has been taken from Madame Curie’s Thesis on the subject:—To extract the uranium, the ore is roasted with sodium carbonate, lixiviated with warm water and then with dilute sulphuric acid, when the uranium passes into solution. The insoluble part consists of the sulphates of lead and calcium, alumina, silica and iron oxide, together with greater or less quantities of nearly all the metals. These residues possess an activity four and one-half times that of uranium, and constitute the raw material used for the extraction of radium.