Thorium (Th)

Thorium is a weakly radioactive.  It has been suggested as a replacement for uranium as nuclear fuel in nuclear reactors, and several thorium reactors have been built. Thorium is also used in strengthening magnesium, coating tungsten wire in electrical and welding equipment, high-temperature crucibles, and glasses including camera and scientific instrument lenses. Other uses for thorium include heat-resistant ceramics, aircraft engines, and in light bulbs. Thorium can form alloys with many other metals.

Starting from 1899, the New Zealand physicist Ernest Rutherford and the American electrical engineer Robert Bowie Owens studied the radiation from thorium; initial observations showed that it varied significantly. It was determined that these variations came from a short-lived gaseous daughter of thorium, which they found to be a new element, now named radon.

In the 1920s, thorium's radioactivity was promoted as a cure for rheumatism, diabetes, and sexual impotence. In 1932, most of these uses were banned in the United States after a federal investigation into the health effects of radioactivity. 10,000 individuals in the United States had been injected with thorium during X-ray diagnosis; they were later found to suffer health issues such as leukaemia and abnormal chromosomes. Public interest in radioactivity had declined by the end of the 1930s.

Non-radioactivity-related uses of thorium have been in decline since the 1950s^[ due to environmental concerns largely stemming from the radioactivity of thorium and its decay products.

Ref:

• Rutherford, E.; Owens, R. B. (1899). "Thorium and uranium radiation". Trans. R. Soc. Can. 2: 9–12.
• Burns, M. (1987). Low-Level Radioactive Waste Regulation-Science, Politics and Fear. CRC Press. pp. 24–25.
• Emsley, J. (2011). Nature's building blocks: an A–Z guide to the elements. Oxford University Press. pp. 544–548.