Thorium, radio-activity

At the time of the discovery of radio-activity, about seventy-five substances were called elements in other words, about seventy-five different substances were known to chemists, none of which had been separated into unlike parts, none of which had been made by the coalescence of unlike substances. Compounds of only two of these substances, uranium and thorium, are radio-active. Radio-activity is a very remarkable phenomenon. So far as we know at present, radio-activity is not a property of the substances which form almost the whole of the rocks, the waters, and the atmosphere of the earth it is not a property of the materials which constitute living organisms. It is a property of some thirty substances—of course, the number may be increased—a few of which are found widely distributed in rocks and waters, but none of which is found anywhere except in extraordinarily minute quantity. Radium is the most abundant of these substances but only a very few grains of radium chloride can be obtained from a couple of tons of pitchblende. 

The number given for radio-active processes has been calculated by assuming that the kinetic energy of the helium atoms emitted, which is of the same order, e.g. for RaC, RtzF, Actin-B, Thorium-B and -C is equal to hv. There is no means of guessing the effect of temperature on the... 

Ruben S, Kamen M, Hassid WZ (1940) Photosynthesis with radioactive carbon II, Chemical properties of the intermediates. J Am Chem Soc 62 3443 Rutherford E (1900) A radio-active substance emitted from thorium compotmds. Phil Mag 49 1 Rutherford E (1906) The mass and velocity of the a particles expelled from radium and actinium. Phil Mag 12 348... 

Rutherford, E. A radio-active substance emitted from thorium compounds. Philos. Mag. 49, 1-14 (1900)... 

Since other projectiles, such as neutrons, protons, and deuterons, have also been used to produce artificial radioactivity, the number of active elements thus created already exceeds by far the number of naturally occurring radio-elements (129, 130, 131). By January, 1940, three hundred and thirty artificial radioactivities had been described these include isotopes of every known element in the range of atomic numbers 1 to 85 inclusive, as well as isotopes of thorium (atomic number 90) and of uranium (atomic number 92) (132). Thus the work of M. and Mme. Joliot-Curie opened up vast avenues of research on the physical, chemical, and radioactive properties of these isotopes and on their therapeutic uses. In 1935 they were awarded the Nobel Prize in chemistry (133). 

---