Exploring Mesothorium: The Radioactive Element in Thorium Minerals

Mesothorium, a radioactive element found in thorium minerals, presents a fascinating study in radioactivity and its applications. This element exists in equilibrium with other isotopes, specifically mesothorium-1, mesothorium-2, and radiothorium, which emit various types of radiation, including alpha, beta, and gamma rays. Notably, mesothorium is significantly more active than radium, with studies indicating that one milligram of mesothorium is equivalent to the activity of approximately 300 milligrams of radium.

The Bureau of Mines has reported that mesothorium is three times more active than radium per unit weight. This high level of activity makes mesothorium a potential candidate for applications where radioactive materials are required, although its commercial use has been limited. The extraction of mesothorium typically occurs from monazite sand, a mineral rich in thorium, which, when processed, can yield small amounts of this radioactive element. For instance, a metric ton of monazite containing 5% thorium oxide can produce about 2.5 milligrams of mesothorium through a 90% extraction process.

Historically, the United States imported monazite in significant quantities, and during World War I, the demand for luminous paints spurred advancements in extraction techniques for mesothorium. These methods exploit the chemical similarities between mesothorium and radium, allowing for their separation. However, extracting mesothorium also results in the concentration of radium, leading to commercial mesothorium being composed primarily of radium chloride, with mesothorium chloride constituting only a small fraction.

Interestingly, while freshly extracted mesothorium is not very effective in applications like luminous paint, its radioactivity enhances as it "ripens" over time, reaching peak alpha radiation after four to five years. This process allows for the emitted beta and gamma radiation to be harnessed in medical applications, similar to radium. However, mesothorium has not gained widespread acceptance in the medical field, partly due to its relatively short half-life, which can drive up costs.

Despite its unique properties, mesothorium remains a rarity in commercial trade and does not have an established market price. Its extraction and use are largely by-products of thorium processing, making it more of a scientific curiosity than a staple in industries reliant on radioactive materials.