Facts About Cesium

Cesium is a rare, silver-white, shiny metal with brilliant blue spectral lines; the element's name comes from "caesius," a Latin word meaning "sky blue." It is the softest metal, with a consistency of wax at room temperature. It would melt in your hands — if it didn't explode first, as it is highly reactive to moisture.

Cesium is a naturally occurring element, although almost never on its own, according to the Jefferson Lab, with a presence in several minerals. It has a density of nearly twice that of water, and is very ductile.

Cesium was the first element to be discovered with a spectroscope. It was discovered in 1860 by German chemists Robert Bunsen and Gustav Kirchhoff when they were analyzing the spectrum of mineral water, according to WebElements.

The first practical applications of cesium were realized in the 1920s, according to the USGS. Cesium was used in vacuum tubes to remove traces of remaining oxygen due to its ready nature to bond with it, and as a coating on heated cathodes to increase the electric current. In later decades, more uses for cesium arose, including photoelectric cells, spectrometers and catalysts for organic reactions. The high cost of cesium and the growing popularity of similar and cheaper technologies using other alkali metals reduced the use of cesium to a handful of applications.

Cesium is currently being researched in treatment of several forms of cancer, including brain tumors, according to a study published in 2016 in the journal Frontiers in Surgery. Cesium-131, a radioactive isotope of cesium, is used with iodine-125, another radioactive isotope, in a brachytherapy seed. According to the American Brachytherapy Society, a brachytherapy seed is a radioactive pod that is placed directly within the cancerous tissue. Brachytherapy seeds have been shown to be effective in several forms of cancer including prostrate, cervical, and endometrial cancers.

The above study refers to a previous study published in 2014 in the Journal of Neurosurgery. In the earlier study, a group of 24 patients with brain tumors had cesium-131 brachytherapy seeds implanted within the tumors. There were minimal side effects, and it was overall a well-tolerated form of treatment.

The idea for using cesium-131 brachytherapy seeds as a treatment for cancer dates back to the 1960s and was described in a study published in the journal Radiology. According to Isoray Medical, cesium-131 was FDA-approved in 2003 with the first trials in 2004. A 2009 study published in the Journal of Medical Physics, discusses using cesium-131 seeds for treatment in prostate cancer with positive results.

And while more research is still needed to understand more about the treatment, all of the studies have shown that using cesium-131 brachytherapy seeds for cancer therapy is encouraging. The authors of the 2016 study state that they are confident that “future studies will likely confirm these promising preliminary results with cesium-based brachytherapy for future treatment of brain metastases.”

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Rachel Ross is a science writer and editor focusing on astronomy, Earth science, physical science and math. She holds a Bachelor of Arts in Philosophy from the University of California Davis and a Master's degree in astronomy from James Cook University. She also has a certificate in science writing from Stanford University. Prior to becoming a science writer, Rachel worked at the Las Cumbres Observatory in California, where she specialized in education and outreach, supplemented with science research and telescope operations. While studying for her undergraduate degree, Rachel also taught an introduction to astronomy lab and worked with a research astronomer.

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