St Ignatius College - Ignatian Yearbook (San Francisco, CA)

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26 THE IGNATIAN spontaneously give out heat and other manifestations of en- ergy which are able to affect a photographifl Plate? to Cause certain substances to fluoresceg and to render the air in their neighborhood a conductor of electricity. These other mani- festations of energy are called rays, and from this comes the term radio-activity. Three different kinds of these rays are 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. Vtfhen uniniiuenccd by external forces they move in straight lines, but under the influence of an electrostatic or a mag- netic 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, un- less 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 are 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 are 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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RADIO-ACTIVE SFBSTANCES 25 duce the Rontgen Rays. Acting on this idea, he examined some iiuoreseent 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 Huoresce. While waiting for a. sunny day, the apparatus was placed in a dark drawer. Two weeks later M. Becquerel 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 Mme. Curie, one of Professor Bet-querel's students made such great progress in this new science. She found that radio-activity is an atomic propertyg that thorium acted like uraniumg that pitchblende carrying a given' weight of uranium had approximately four times greater activity than any pure uranium salt containing the same weight of ura- nium. This latter disclosure caused Mme. Curie to conclude that pitchblende contained another element 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, stron- tium, and calcium group. After the calcium and strontium had been eliminated, the barium that remained still showed strong activity. This caused Mme. Curie to investigate fur- ther, 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 ELEMENTS. The elements uranium, thorium, radium, polonium and actinium are radio-active, and by that is meant that they

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RADIO-ACTIVE SUBSTANCES 27 RADIUM. Radium is the only new 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 ra- dium 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 correspond- ingly 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. Wleiglit for weight, the radium compounds are 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 or EXTRACTION. , Radium is now obtained chiefly from carnotite, though a small amount is derived from pitchblende. Practically all of the world's radium until nine years ago, came from de- posits 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 earnotite ore was erected in Colorado in 1900. The following method of the treatment of radium extrac- tion has been taken from Madame Curie's Thesis on the subject :-To extract the uranium, the ore is roasted with so- dium earbonate, 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 cal- cium, alumina, silica and iron oxide, together with greater or less quantities of nearly all the metals. These residues pos- sess an activity four and one-half times that of uranium, and constitute the raw material used for the extraction of radium.