Pierre Curie

“ Induced Radioactivity.—Radium, thorium, and actinium have the property of acting externally, apart from the Becquerel rays that they emit. They communicate little by little their radioactive properties to substances in their neighborhood, and the latter emit in turn Becquerel rays. The activity can be transmitted to gases, liquids, and solids. The phenomenon is known as induced radioactivity.
Induced radioactivity propagates itself in gases step by step by a sort of conduction, and is not at all due to direct radiation from the body which causes it. ”

“ One can foresee the possibility of establishing mechanics upon the dynamics of small material centers charged and in motion.
α-Rays.—The α-rays of radium have very little power of penetration. A piece of aluminium foil a few hundredths of a millimeter in thickness absorbs them almost completely. They are also absorbed by the air, and cannot penetrate air at the atmospheric pressure to a greater distance than 10 cm. The α-rays form the most important part of the radiation of radium, provided we measure the radiation by the amount of ionization which it produces in the air. ”

“ When the magnetic field acts alone the different β-rays are unequally deflected but remain in a plane normal to the field, producing upon the plate an impression in the form of a straight line. When the electric field acts alone the different β-rays are unequally deflected in a plane passing through the field and producing upon the plate an impression which is a straight line perpendicular to the one preceding. When both fields act simultaneously the impression on the plate is a curve. ”

“ The plate of lead is entirely covered with a layer of paraffin, which is in turn enveloped in fine aluminium foil connected with the earth. The radium, placed in a small dish, sends its rays upon the plate of lead, which is thus protected. The α-rays are stopped by the exterior layer of aluminium. Part of the β-rays pass through the aluminium and the paraffin and are absorbed by the lead, which becomes charged negatively. The paraffin is necessary to sufficiently insulate the plate of lead, which could be charged if it were surrounded by air, for it is made a conductor by Becquerel rays. ”

“ Uranium and Thorium.—We call radioactive such substances as are capable of emitting spontaneously and continuously certain rays known as Becquerel rays. These rays act upon the photographic plate; they render the gases through which they pass conductors of electricity; they can pass through black paper and metals. The Becquerel rays cannot be reflected, refracted or polarized. ”

“ The salts of radium continually give off heat. Its amount is sufficient for it to be detected by means of a crude experiment with two ordinary mercury thermometers. Two identical heat-insulating vacuum-bulbs are used. In one of these is placed a glass bottle containing 0.7 gram of pure radium bromide; in the second is placed a glass bottle containing some inactive substance, such as barium chloride. The temperature of the contents of each is shown by a thermometer placed with its bulb near the bottle. ”

“ It seems from this that the emanation experiences some particular difficulty in escaping from radium which is in a vacuum.
Disengagement of Gas by the Salts of Radium. Production of Helium.—Giesel noticed that solutions of radium bromide continually give off gases. These gases are principally hydrogen and oxygen, in the same relative proportion as in water, and might, therefore, come from the decomposition of the water of the solution. But Ramsay and Soddy also showed that there always is a small quantity of helium that they detected by its spectrum in a Geissler tube. ”

“ Suppose the β-rays to be projectiles (electrons) negatively charged with electricity and shot from the radium with great velocity. Let be the mass of a projectile, its charge, its initial velocity, the radius of curvature of its path, the intensity of the magnetic field normal to the initial velocity, the magnetic permeability of the medium. We then have the easily established relation
The β-rays are also deviated in an electric field. ”

“ II.) , filled with air, communicates through the constricted part, , with the bulb, , which contains radium, . At the end of a certain time the emanation has spread into , and its interior walls have become active. The receiver, , is then separated from the radium by closing with a flame. The external radiation of may then be studied by placing it in the interior cylinder of a cylindrical condenser (Fig. III.) . The interior cylinder is of aluminium, . It is brought to a potential of 500 volts. The external cylinder, , of the condenser is of copper. ”

“ Action on the Eye.—Giesel: Naturforscherversammlung, 1899; Himstedt and Nagel: Ann. Phys., 4, 1901.
Physiological Action.—Aschkinas and Caspari: Ann. Phys., 6, 570 (1901) ; Danysz: Compt. rend., Feb. 16, 1903; Bohn: Ibid., April 27 and May 4, 1903. Treatment of Lupus.—Danlos: Soc. ”