Fig. 6.Fig. 6.—Disintegration Series for Uranium, Actinium, and Thorium, as Given by Soddy.
Disintegration of the Elements
The remarkable disintegrations related in the last chapter, in which the heaviest known elementary atom—that of uranium (at. wt. 238)—is by successive stages changed into others of lower atomic weight, afford a clue to the nature of the atom and to that goal of the chemist, the final constitution of matter. The composite nature of the atom and some sort of interrelation of the elements had previously been made apparent from a study of the Periodic System and data gathered still earlier, but all attempts at working out a so-called genesis of the elements had proved vague and unsatisfactory.
Identification of the Rays
To get an understanding of the disintegration occurring in radio-active substances, the nature of the rays produced must be known. These rays are the cause of the activity and their emission accompanies the changes or disintegration. They have for the sake of convenience been called the alpha, beta, and gamma rays. The gamma rays have been identified with theXrays discovered by Röntgen and are a form of energy analogous to light. The beta rays are particles of negative electricity or electrons. Withthese, then, we have some degree of familiarity. But what are the alpha rays? An answer to this question should make clearer the character of the changes taking place, and should give some insight into the composition and mechanism of the atom.
The Alpha Rays
It has already been stated that these alpha rays are similar or analogous to the canal rays, but this advances the matter very little, as the nature of these canal rays has not been fully determined. The full identity with them, if proved, should have an important theoretical bearing.
Alpha Rays Consist of Solid Particles
In the first place, these alpha rays have been found to be made up of solid particles, that is, of what we are accustomed to call matter. Since it has become more and more difficult to draw a clear distinction between matter and energy, it would perhaps be better to say that these particles appear to have some of the properties hitherto attributed solely to matter. The best evidence that these particles are of atomic mass is furnished by their deflection in electric and magnetic fields.
Electrical Charge
It is not of first importance to discuss this or other proofs of the material nature of these particles. That they carry a charge of positive electricity is, however, a fact of very great import. The value of this charge has been carefully determined by a number of investigators working with different sources of the alpha particles and has been found tobe 9.3 × 10-10electrostatic units (.000,000,000,93 e.s.). From the consideration of the charge upon an electron previously obtained by J. J. Thomson and others, it was concluded that the alpha particle carried two unit positive charges; the fundamental unit charge, therefore, is half this value, or 4.65 × 10-10e.s.
Helium Formed from Alpha Particles
To determine the nature of the alpha particle a crucial experiment was carried out by Rutherford and Royds, which was described as follows:
Fig. 7.Fig. 7.—Apparatus Used in Experiment by Rutherford and Royds.
A large quantity of radium emanation was compressed into a fine glass tubeA, about 1.5 cm. long. This tube, which was sealed to a larger capillary tubeB, was sufficiently thin to allow the alpha particles from the emanation and its products to pass through, but sufficiently thick to withstand atmospheric pressure. The thickness of the glass wall was in most cases less than .01 mm. On introducing the emanation into the tube, the escape of the alpha particles from the emanation was clearly seen by the scintillations produced at some distance on a zinc sulphide screen. After this test the glass tubeAwas surrounded by a glass tubeTand a small spectrum tubeVattached to it. The tubeTwas exhausted to a charcoal vacuum. By means of the mercury columnH, the gases in the tubeTcould at any time be compressed into the spectrum tubeVand the nature of the gases which had been produced determined spectroscopically. It was found that two days after the introduction of the emanation intoAthe spectrum showed the yellow line of helium, and after six days the whole helium spectrum was observed. In order to be certain that the helium, coming possibly from some other source, had not diffused through the thin walls of the tubeA, the emanation was pumped out and helium substituted. No trace of helium could be observed in the vacuum tube after several days, showing that the helium observed in the first experiment must have originated from the alpha particles which had been propelled through the thin glass tube into the outer tube.
Most of the alpha particles are propelled with such force that they penetrate some distance into the walls of the outer tube and some of these gradually diffuse out into the exhausted space. The presence of helium in the spectrum tube can be detected after a shorter interval if a thin cylinder of lead is placed over the emanation tube, since the particles fired into the lead diffuse out more rapidly than from glass.
A still more definite proof of the identity of the alpha particle with the helium atom was obtained by removing the outer glass tubeTand placing a cylinder of lead over the emanation tube in the open air. Helium wasalways detected in the lead after it had remained several hours over the thin tube containing a large quantity of the emanation. In order to test for the presence of helium in the lead, the gases present were released by melting the lead in a closed vessel. There can thus be no doubt that the alpha particle becomes a helium atom when its positive charge is neutralized.
Thus the chemist was afforded the experience of the building up of at least one element under his observation, and both the analysis and synthesis of matter have been revealed through the discoveries of radio-activity.
Discovery of Helium
It is of interest at this point to learn something of the history of helium and its occurrence. In 1868 there was discovered by Janssen and Lockyer a bright yellow line in the spectrum of the sun's chromosphere. Because of its origin the name helium was given to the supposed new element causing it. Later it was found in the spectra of many of the stars, and because of its predominance in some of these they were called helium stars. Its existence on our planet was not detected for nearly thirty years.
In 1895, in connection with the discovery of argon in the atmosphere, a search was made to see if the latter element could be obtained from mineral sources. In analyzing certain uranium minerals Hillebrand had found considerable quantities of a gas which he took to be a peculiar form of nitrogen. Ramsay made a further examination of the gas coming from these minerals andthe spectroscope revealed the yellow line of helium, thus at last proving the presence of this element on the earth. It is known now to be present in thorium minerals, in the waters of radio-active wells, and in minute amounts in the atmosphere. Its occurrence in every case, in the light of the experiment described above, would seem to be due to the presence of radio-active changes.
Characteristics of Helium
Helium, on account of its chemical inactivity and physical properties, is classed along with argon, neon, krypton, and xenon in the zero group of the Periodic System, and forms with them the monatomic, inert gases. In this class are now placed also the three radio-active gases, emanating respectively from radium, thorium, and actinium. These are generally known as radium emanation, thorium emanation, and actinium emanation. The first mentioned was once called niton. Emanium was the name originally proposed by Giesel for the body now known as actinium.
The calculated rate of production of helium in the series in equilibrium with one gram of radium is 158 cubic millimeters per year. This corresponds quite well with the experimental results.
Table of Constants
Some of the more important atomic and radio-active constants are given in the following table. They are recorded here to show how helpful the study of radio-activity has been in working out the composition of matter, and to give some idea ofthe magnitude of the numbers and the minuteness of the quantities dealt with.
[1]The expression 10-10means multiplying by .000,000,000,1; 1010means multiplying by 10,000,000,000.
[1]The expression 10-10means multiplying by .000,000,000,1; 1010means multiplying by 10,000,000,000.
Properties of Radium
A study of the properties of radium will aid in throwing light upon the question as to the building up of the atom. First to be considered are the usual properties which distinguish an elementary body. Metallic radium has been prepared by a method similar to that used in the preparation of barium. It is a pure white metal, melting at 700°, and far more volatile than barium. It rapidly alters on exposure to the air, probably forming a nitride. It energetically decomposes water and the product dissolves in the water. Its atomic weight is 226.
Radium forms a series of salts analogous in appearance and chemical action to those of barium. In the course of time they become colored, especially if mixed barium salts. The radiations from radium produce marked chemical effects in a number of substances. Carbon dioxide is changed into carbon, oxygen, and carbon monoxide, and the latter is changed into carbon and oxygen. Ammonia is dissociated into nitrogen and hydrogen; hydrochloric acid into chlorine and hydrogen. Oxygen is condensed into ozone. In general, the action upon gases appears to be similar to thatof the silent electric discharge. Water is decomposed into hydrogen and oxygen. If moist radium chloride or a salt of radium containing water of crystallization is sealed in a glass tube, the gradual accumulation of hydrogen and oxygen will burst the tube.
The radiations rapidly decompose organic matter with the evolution of gases. Thus grease from stopcocks of apparatus used with radium or paraffin will give off carbon dioxide. Under an intense alpha radiation paraffin or vaseline become hard and infusible. White phosphorus is changed into red.
The action upon living tissue is most noteworthy, as its possible use as a remedial agent is dependent upon this. A small amount of a radium salt enclosed in a glass tube will cause a serious burn on flesh exposed to it. It therefore has to be handled with care and undue exposure to the radiations must be avoided. Cancer sacs shrivel up and practically disappear under its action. Whether the destruction of whatever causes the cancer is complete is at least open to serious doubt.
The coagulating effect upon globulin is interesting. When two solutions of globulin from ox serum are taken and acetic acid added to one while ammonia is added to the other, the opalescence in drops of the former is rapidly diminished on exposure to radium, showing a more complete solution, whereas the latter solution rapidly turns to a jelly and becomes opaque, indicating a greatly decreased solubility.
Energy Evolved by Radium
The greater part of the tremendous energy evolvedby radium is due to the emission of the alpha particles, and in comparison the beta and gamma rays together supply only a small fraction. This energy may be measured as heat. It was first observed that a radium compound maintained a temperature several degrees higher than that of the air around it. The rate of heat production was later measured by means of an ice calorimeter and also by noting the strength of the current required to raise a comparison tube of barium salt to the same temperature. Both methods showed that the heat produced was at the rate of about 135 gram calories per hour. As the emission is continuous, one gram of radium would therefore emit about 1,180,000 gram calories in the course of a year. At the end of 2000 years it would still emit 590,000 gram calories per year. Such a production of energy so far surpasses all experience that it becomes almost inconceivable. It is futile to speak of it in terms of the heat evolved by the combustion of hydrogen, which is the greatest that can be produced by chemical means.
This effect is unaltered at low temperatures, as has been tested by immersing a tube containing radium in liquid air. It should be stated that these measurements were made after the radium had reached an equilibrium with its products; that is, after waiting at least a month after its preparation. The evolution of heat from radium and the radio-active substances is, in a sense, a secondary effect, as it measures the radiantenergy transformed into heat energy by the active matter itself and whatever surrounds it. Let us repeat, therefore, that the total amount of energy pent up in a single atom of radium almost passes our powers of conception.
Necessity for a Disintegration Theory
The facts gathered so far justify and necessitate a theory which shall satisfactorily explain them, and since these phenomena are not caused by nor subject to the influence of external agencies, they must refer to changes taking place within the atom—in other words, a theory of disintegration. In the main, these facts may be summed up as the emission of certain radiations from known elemental matter: the material alpha particles with positive charge, the beta particles or negative electrons, and the gamma rays analogous toXrays. The emission of these rays results in the production of great heat. Then there is the law of transformations by which whole series of new elements are generated from the original element and maintain a constant equilibrium of growth and decay in the series. Lastly, we have the production of helium from the alpha particles.
Disintegration Theory
In explanation of these phenomena, Rutherford offered the hypothesis that the atoms of certain elements were unstable and subject to disintegration. The only elements definitely known to come under this description are the two having atoms of the greatest known mass, thorium (232) and uranium (238).
The atoms of uranium, for instance, are supposed to be not permanent but unstable systems. According to the hypothesis, about 1 atom in every 1018becomes unstable each second and breaks up with a violent explosion for so small a mass of matter. One, or possibly two alpha particles are expelled with great velocity. This alpha particle corresponds to an atom of helium with an atomic weight of 4, and its loss reduces the original atomic weight to 234 with the formation of a new element, having changed properties corresponding to the new atomic weight. This new element is uraniumX1.
These new atoms are far more unstable than those of uranium, and the decomposition proceeds at a new rate of 1 in 107per second. So at a definite, measurable rate this stepwise disintegration proceeds. The explosions are not in all cases equally violent in going from element to element, nor are the results the same. Sometimes alpha particles alone are expelled, sometimes beta, or two of them together, as alpha and beta.
The new product may remain with the unchanged part of the original matter. Thus there would be an accumulation of it until its own decay balances its production, resulting eventually in a state of equilibrium.
Constitution of the Atom
In order to explain the electrical and optical properties of matter, the hypothesis was made that the atom consisted of positively and negatively electrified particles. Later it was shown that negative electrons exist in all kinds of matter.Various attempts were made to work out a model of such an atom in which these particles were held in equilibrium by electrical forces. The atom of Lord Kelvin consisted of a uniform sphere of positive electrification throughout which a number of negative electrons were distributed, and J. J. Thomson has determined the properties of this type as to the number of particles, their arrangement and stability.
Rutherford's Atom
According to Rutherford, the atom of uranium may be looked upon as consisting of a central charge of positive electricity surrounded by a number of concentric rings of negative electrons in rapid motion. The positively charged centre is made up of a complicated system in movement, consisting in part of charged helium and hydrogen atoms, and practically the whole charge and mass of the atom is concentrated at the centre. The central system of the atom is from some unknown cause unstable, and one of the helium atoms escapes from the central mass as an alpha particle.
There are, confessedly, difficulties connected with this conception of the atom which need not, however, be discussed here. Much remains to be learned as to the mechanics of the atom, and the hypothesis outlined above will probably have to be materially altered as knowledge grows. Perhaps it may have to be entirely abandoned in favor of some more satisfactory solution. Until such time it at least suffices as a mental picture around which the known facts group themselves. Inthis picture energy and matter lose their old-time distinctness of definition. Discrete subdivisions of energy are recognized which may be called charged particles without losing their significance. Some of these subdivisions charged in a certain way or with neutralized charge exhibit the properties of so-called matter.
Scattering of Alpha Particles
This conception of the atom would doubtless fail of much support were it not for certain experimental facts which lend great weight to it. Certain suppositions can be based on this theory mathematically reasoned out and tested by experiment. Predictions thus based on mathematical reasoning and afterward confirmed by experiment give a very convincing impression that truth lies at the bottom.
The first of these experimental proofs comes under the head of what is known as the scattering of the alpha particles, a phenomenon which, when first observed, proved hard to explain. If an alpha particle in its escape from the parent atom should come within the influence of the supposed outer electrical field of some other atom, it should be deflected from its course and, the intensity of the two charges being known, the angle of deflection could be calculated. For instance, if it came to what might be called a head-on collision with the positive central nucleus of another atom, it would recoil if it were itself of lesser mass, or would propel the other forward if that were the lighter.
The experiment is carried out by placing a thin metal foil over a radio-active body, as radiumC, which expels alpha particles with a high velocity, and counting the number of alpha particles which are scattered through an angle greater than 90° and so recoil toward their source. This has been done by a number of investigators and it has been found that the angle of scattering and the number of recoil particles depend upon the atomic weight of the metal used as foil. For example, if gold is used, the number of recoil atoms is one in something less than 8,000.
Taking the atomic weight of gold into consideration, Rutherford calculated mathematically that this was about the number which should be driven backward. But he went further and calculated also the number which should be returned by aluminum, which has an atomic weight of only about one-seventh that of gold. Two investigators determined experimentally the number for aluminum and their results agreed with Rutherford's calculations.
The metals from aluminum to gold have been examined in this way. The number of recoil particles increases with the atomic weight of the metal. Comparing experiment with theory, the central charge in an atom corresponds to about one-half the atomic weight multiplied by the charge on an electron, or, as it is expressed, ½ Ae.
There is only one lighter atom than helium, namely, hydrogen, which has a mass only one-fourth as great.When alpha particles are discharged into hydrogen, a few of the latter atoms are found to be propelled to a distance four times as great as that reached by the alpha particles.
Stopping Power of Substances
Parallel with the experiments mentioned, there is what is called the stopping power of substances. This means the depth or thickness of a substance necessary to put a stop to the course of the alpha particles. This gives the range of the alpha particles in such substances and is connected in a simple way with the atomic weight, that is, it is again fixed by the mass of the opposing atom. This stopping power of an atom for an alpha particle is approximately proportional to the square root of its atomic weight.
Considering gases, for instance, if the range in hydrogen be 1, then the range in oxygen, the atomic weight of which is 16, is only √(1/16) or ¼. Generally in the case of metals the weight of matter per unit area required to stop the alpha particle is found to vary according to the square root of the atomic weight of the metal taken.
Influence upon Chemical Theory
It can easily be seen that the revelations of radio-activity must have a far-reaching effect upon chemical theory, throwing light upon, and so bringing nearer, the solution of some of the problems which have been long discussed without arriving at any satisfactory solution. The so-called electro-chemical nature of the elements will certainly be made much clearer. The changes in valence should become intelligible and valence itself should be explained. A fuller understanding of the ionization of electrolytes also becomes possible. As these matters are debatable and the details are still unsettled, it is scarcely appropriate to give here the hypotheses in detail or to enter into any discussion of them. But the promise of solution in accord with the facts is encouraging.
The Periodic System
Such progress has been made, however, in regard to a better understanding of the Periodic System that the new facts and their interpretation may well be given. No reliable clue to the meaning of this system and the true relationship between theelements had been found up to the time when new light was thrown upon it by the discoveries of radio-activity. The underlying principle was unknown and even the statement of what was sometimes erroneously called the Periodic Law was manifestly incorrect and its terms were ignored.
Basis of the Periodic System
The ordinary statement of the fundamental principle of the Periodic System has been that the properties of the elements were periodic functions of the atomic weights, and that when the elements were arranged in the order of their atomic weights they fell into a natural series, taking their places in the proper related groups.
In accepting this, the interpretation of function was both unmathematical and vague, and the order of the atomic weights was not strictly adhered to but unhesitatingly abandoned to force the group relationship. Wherever consideration of the atomic weight would have placed an element out of the grouping with other elements to which it was clearly related in physical and chemical properties, the guidance of these properties was accepted and that of the atomic weights disregarded. Such shiftings are noted in the cases of tellurium and iodine; cobalt and nickel; argon and potassium. It was most helpful that, following the order of atomic weights, the majority of the elements fell naturally into their places. Otherwise the generalization known as the Periodic System mighthave remained for a long time undiscovered and the progress of chemistry would have been greatly retarded.
Influence of Positive Nucleus
It is evident that the order of the elements is determined by something else than their atomic weights. From the known facts of radio-activity it would seem that this determining factor is the positive nucleus. And this nucleus also determines the mass or weight of the atom. Taking the elements in their order in the Periodic Series and numbering the positions held by them in this series as 1, 2, 3, etc., we get the position number or what is called the atomic number. This designates the order or position of the element in the series. We must learn that this number marks a position rather than a single element, a statement which will be explained later.
Determination of the Atomic Number
Since the atomic weight is unreliable as a means of settling the position of an element in the series and so fixing its atomic number, how is this number to be determined? Of course, one answer to this question is that we may rely upon a consideration of the general properties, as has been done in the past. Fortunately, other methods have been found by which this may be confirmed. For instance, the stopping and scattering power of the element for alpha particles has been suggested and successfully used.
Use of X-Ray Spectra
A most interesting method is due to Moseley'sobservations upon theX-ray spectra of the various elements. It has been found that crystals, such as those of quartz, have the power of reflecting and defining theXrays. The spectra given by these rays can be photographed and the wave lengths measured. TheseXrays are emitted by various substances under bombardment by the cathode rays (negative electrons) and have great intensity and very minute wave lengths. Moseley made use of various metals as anti-cathodes for the production of these rays. These metals ranged from calcium to zinc in the Periodic System. In each case he observed that two characteristic types ofXrays of definite intensity and different wave lengths were emitted. From the frequency of these waves there is deduced a simple relation connected with a fundamental quantity which increases in units from one element to the next. This is due to the charge of the positive central nucleus. The number found in this way is one less than the atomic number. Thus the number for calcium is 19 instead of 20 and that for zinc is 29 instead of 30. So, by adding 1 to the number found the atomic number is obtained.
The atomic weight can usually be followed in fixing the atomic number, but where doubt exists the method just given can be resorted to. Thus doubt arises in the case of iron and nickel and cobalt. This would be the order according to the atomic weights. TheX-ray method gives the order as iron, cobalt, andnickel, and this is the accepted order in the Periodic System.
Changes Caused by Ray Emission
On studying the properties of the elements in a transformation series in connection with the ray emission which produced them, it was seen that these properties were determined in each case by the nature of the ray emitted from the preceding transformation product or parent element.
Atomic Weight Losses
Each alpha particle emitted means a loss of 4 in the atomic weight. This is the mass of a helium atom. Thus from uranium with an atomic weight of 238 to radium there is a loss of three alpha particles. Therefore, 12 must be subtracted from 238, leaving 226, which agrees closely with the atomic weight of radium as actually determined by the ordinary methods. UraniumX1, then, would have an atomic weight of 234 and that of ionium would be 230. The other intermediate elements, whose formation is due to the loss of beta particles only, show no decrease in atomic weight.
Lead the End Product
From uranium to lead there is a loss of 8 alpha particles, or 32 units in atomic weight. This would give for the final product an atomic weight of 206. The atomic weight of lead is 207.17. It is not at all certain that the final product of this series is ordinary lead. The facts are such that they would lead one to think that it is not. It is known only that the end product would probably be some element closely resembling lead chemically and hencedifficult or impossible to separate from it. Several accurate determinations of lead coming from uranium minerals, which always carry this element and in an approximately definite ratio to the amount of uranium present, show atomic weights of 206.40; 206.36; and 206.54. Even the most rigid methods of purification fail to change these results. The lead in these minerals might therefore be considered as coming in the main from the disintegration of the uranium atom and, though chemically resembling lead, as being in reality a different element with different atomic weight.
Furthermore, in the thorium series 6 alpha particles are lost before reaching the end product, which again is perhaps the chemical analogue of lead. The atomic weight here should be 232 less 24, or 208. Determinations of the atomic weight of lead from thorite, a thorium mineral nearly free from uranium, gave 208.4.
The end product of the actinium series is also an element resembling lead, but both the beginning and ending of this series are still in obscurity.
Changes of Position in the Periodic System
The loss of 4 units in the atomic weight of an element on the expulsion of an alpha particle is accompanied by a change of chemical properties which removes the new element two groups toward the positive side in the Periodic System.
Thus ionium is so closely related to thorium and so resembles it chemically that it is properly classed along with thorium as a quadrivalent element in the fourthgroup. Ionium expels an alpha particle and becomes radium, which is a bivalent element resembling barium belonging to the second group. Radium then expels an alpha particle and becomes the gas, radium emanation, which is an analogue of argon and belongs to the zero group. Other instances might be cited which go to show that in all cases the loss of an alpha particle makes a change of two places toward the left or positive side of the System.
Changes from Loss of Beta Particles
The loss of a beta particle causes no change in the atomic weight but does cause a shift for each beta particle of one group toward the right or negative side of the System. Two such losses, then, will counterbalance the loss of an alpha particle and bring the new element back to the group originally occupied by its progenitor. Thus uranium in the sixth group loses an alpha particle and the product UX1falls in the fourth group. One beta particle is then lost and UX2belonging to the fifth group is formed. With the loss of one more beta particle the new element returns to the sixth group from which the transformation began.
The table on page 48, as adapted from Soddy, affords a general view of these changes.
Fig. 6.Radio-active Elements from Uranium and Thorium Placed in the Periodic SystemsAdapted from Soddy
Isotopes
An examination of the table will show a number of different elements falling in the same position in a group of the Periodic System irrespective of their atomic weights. These are chemically inseparable so far as the present limitations ofchemical analysis are concerned. Even the spectra of these elements seem to be identical so far as known. This identity extends to most of the physical properties, but this demands much further investigation. For this new phenomenon Soddy has suggested the word isotope for the element and isotopic for the property, and these names have come into general use.
Manifestly, we have come across a phenomenon here which quite eliminates the atomic weight as a determining factor as to position in the Periodic or Natural System or of the elemental properties in general. All of the properties of the bodies which we call elements, and consequently of their compounds and hence of matter in general, seem to depend upon the balance maintained between the charges of negative and positive electricity which, according to Rutherford's theory, go to make up the atom.
It is evident that any study of chemical phenomena and chemical theory is quite incomplete without a study of radio-activity and the transformations which it produces.
Radio-activity in Nature
In concluding this outline of the main facts of radio-activity, it is of interest to discuss briefly the presence of radio-active material on this planet and in the stars. Facts enough have been gathered to show the probable universality of this phenomenon of radio-activity. Whether this means solely the disintegration of the uranium and thoriumatoms, or whether other elements are also transformed under the intensity of the agencies at work in the universe, is of course a question as yet unsolved.
Radio-active Products in the Earth's Crust
The presence of uranium and thorium widely distributed throughout the crust of the earth would lead to the conclusion that their disintegration products would be found there also. Various rocks of igneous origin have been examined revealing from 4.78 × 10-12to 0.31 × 10-12grams of radium per gram of the rock. Aqueous rocks have shown a lesser amount, ranging from 2.92 × 10-12to 0.86 × 10-12grams. As the soil is formed by the decomposition of these rocks, radium is present in varying amounts in all kinds of soil.
Presence in Air and Soil Waters
As radium is transformed into the gaseous emanation, this will escape wherever the soil is not enclosed. For instance, a larger amount of radio-activity is found in the soil of caves and cellars than in open soils. If an iron pipe is sunk into a soil and the air of the soil sucked up into a large electroscope, the latter instrument will show the effect of the rays emitted and will measure the degree of activity. Also the interior of the pipe will receive a deposit of the radio-active material and will show appreciable radio-activity after being removed from the soil.
This radium emanation is dissolved in the soil waters, wells, springs, and rivers, rendering them more or less radio-active, and sometimes the muddy deposit at the bottom of a spring shows decided radio-activity.
The emanation also escapes into the air so that many observations made in various places show that the radium emanation is everywhere present in the atmosphere. Neither summer nor winter seems to affect this emanation, and it extends certainly to a height of two or three miles. Rain, falling through the air, dissolves some of the emanation, so that it may be found in freshly-fallen rain water and also in freshly-fallen snow. Radio-active deposits are found upon electrically charged wires exposed near the earth's surface.
As helium is the resulting product of the alpha particles emitted by the emanation and other radio-active bodies, it is found in the soil air, soil waters, and atmosphere.
Average measurements of the radio-activity of the atmosphere have led to the calculation that about one gram of radium per square kilometer of the earth's surface is requisite to keep up the supply of the emanation.
A number of estimates have been given as to the heat produced by the radio-active transformations going on in the material of this planet. Actual data are scarce and mere assumptions unsatisfactory, so little that is worth while can be deduced. It is possible that this source of heat may have an appreciable effect upon or serve to balance the earth's rate of cooling.
Cosmical Radio-activity
Meteorites of iron coming from other celestial bodies have not shown the presence of radium. Aerolites or stone meteorites have been found to contain as much as similar terrestrial rock.Since the sun contains helium and some stars show its presence as predominating, this suggests the presence of radio-active matter in these bodies. In addition, the spectral lines of uranium, radium, and the radium emanation have been reported as being found in the sun's spectrum and also in the new star,Nova Geminorum 2. These observations await further investigation and confirmation. So far as the sun's chromosphere is concerned, the possible amount of radium present would seem to be very small. If this is true, radio-active processes could have little to do with the sun's heat. The statement is made by Rutherford that indirect evidence obtained from the study of the aurora suggests that the sun emits rays similar in type to the alpha and beta rays. Such rays would be absorbed, and the gamma rays likewise, in passing through the earth's atmosphere and so escape ordinary observation. All of this is but further evidence of the unity of matter and of forces in the universe.
Actinium, discovery of,6Activity, induced,17Alpha particles, effect of loss on Atomic Weight,45electrical charge of,26form helium,27nature of,25penetrating power of,39position of element changed by its loss,46recoil,39scattering of,38solid,26Atom, constitution of,36Kelvin's,37models of,37Rutherford's,37Atomic number, determination of,43Becquerel's experiments,2Beta particles, change in position of element by loss of,47Chalcolite, natural and artificial,4Constants, table of,31Curie unit,22Disintegration of the element,25Disintegration series,24Disintegration theory,35Electroscope,12Equilibrium series,22Helium, characteristics of,30discovery of,29Ionium, discovery of,6Ionization, application of electric field to,10experimental confirmation,9Ionization of gases,7theory of,8Ions, size and nature of,10Isotopes,47Lead, atomic weight varies with source,45radio-active,6the end product,45Life-periods of radio-active bodies,21Periodic system,41basis of,42Polonium, discovery of,4Positive nucleus, influence of,43Potassium, radio-activity of,3Radiations, action on phosphorescent bodies,13action on photographic plates,11discharge electrified bodies,12magnetic deflection of,14measurements of,15penetrating power of,13,15Radio-active bodies, elemental nature of,20examination of,20life periods of,21Radio-activity, an atomic property,3cosmical,51influence on chemical theory,41products in atmosphere,51products in earth's crust,50products in soil waters,50Radium, action on organic matter, etc.,33amount in pitchblende,5discovery of,5emanation,22energy evolved by,34properties of,5,32Rays, alpha,15,16,26beta,15,16gamma,15,16identification of,16,25magnetic deflection of,14photographing track of,10types of,14Rubidium, radio-activity of,3Spinthariscope,13Stopping power of substances,39Thorium X, discovery of,18,21Uranium atom, disintegration of,36Uranium minerals, radio-activity of,3Uranium X, discovery of,17,21,23X-ray spectra,44Zinc sulphide screen,13
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