By P. CURIE.
[Reprinted from the American Chemical Journal, Vol. XXXI, No. 4.April, 1904.]
RECENT RESEARCH ON RADIOACTIVITY.[1]
By P. Curie.
Since the discovery of strongly radioactive substances, research onradioactivity has been greatly developed. I propose in this article togive an account of the actual state of our knowledge relative to thissubject, laying particular stress on the most recent work.[2]
[1]Translated from an article that appeared in Jour. d. Chim.Phys., I, 409 (1903) edited by Philippe A. Guye, Professor of Chemistryin the University of Geneva. See THIS JOURNAL, 31, 298 (1904).
[2]For more complete details of work done previous to May,1903, see the thesis of Mme. Curie. It appeared in Ann. de Chim. et dePhys. in 1903 and 1904.
I. Radioactive Substances.
Becquerel Rays. Uranium and Thorium.—We callradioactive such substances as are capable of emitting spontaneously andcontinuously certain rays known as Becquerel rays. These rays act uponthe photographic plate; they render the gases through which they passconductors of electricity; they can pass through black paper and metals.The Becquerel rays cannot be reflected, refracted or polarized.
In 1896 Becquerel discovered that uranium and its compounds emit thesenew rays continuously. Schmidt and Mme. Curie then found almostsimultaneously that thorium compounds are also radioactive. Theradiations emitted by thorium compounds are comparable in intensity withthose from the compounds of uranium. Radioactivity is an atomic propertythat accompanies the atoms of uranium and thorium wherever they arefound; in a compound or a mixture its intensity is proportional to theamount of the metal present.
New Radioactive Substances.—Mme. Curie, in 1898, tried tolearn whether there were among the elements then known any otherspossessing radioactivity; she could not find a single substance givingany considerable radiation, and concluded that the radioactiveproperties of the elements are at least 100 times more feeble than thoseof uranium and thorium. She found, on the other hand, that certainminerals containing uranium (pitchblende, chalcolite, and carnotite) aremore active than metallic uranium; the activity of these minerals couldnot, then, be due solely to uranium or to other known elements. Thisdiscovery was fertile with new results. Mme. Curie and I showed, in aninvestigation carried on together, that pitchblende contains newradioactive substances, and we supposed that these substances containednew chemical elements.
There are known with certainty three new strongly radioactivesubstances: polonium, which was found in the bismuth obtained from theuranium minerals; radium, found with barium from the same source, andactinium, which was discovered by Debierne among the rare earthsextracted from the same minerals. These three substances are presentonly in infinitesimal quantities in the uranium minerals, and all threepossess a radioactivity about a million times gr