Archived Content

Information identified as archived on the Web is for reference, research or recordkeeping purposes. It has not been altered or updated after the date of archiving. Web pages that are archived on the Web are not subject to the Government of Canada Web Standards. As per the Communications Policy of the Government of Canada, you can request alternate formats by contacting us.

Cesium

Cesium, named for the bright blue light emitted upon thermal excitation is a very soft, silvery-gold metal. This extremely reactive element rapidly oxidizes in air and can cause severe burns to the skin upon contact.

In spite of its reactive nature, cesium has important applications. Many of its compounds contribute to the function of alkaline storage batteries and to the production of special glasses. One of cesium's isotopes, Cs-137, is manufactured in nuclear reactors and shipped to hospitals for use in radiation therapy.

Natural, non-radioactive cesium is renowned for its role in timekeeping around the world. Today, the National Research Council Canada (NRC) is the official timekeeper in Canada. Researchers helped end the era of astronomical timekeeping when they completed the construction of NRC's first cesium clock in 1958. A cesium clock's extreme precision – now accurate to about a second in a million years – is a function of the stability of the inner structure of cesium atoms. The frequency of a specific transition between two of cesium's energy levels can be accurately monitored and thus used to define the standard unit of time – the second.

An important application of this accuracy is seen in the Global Positioning System where the navigation system relies on the signals broadcast from atomic clocks found on satellites orbiting the earth.

Currently, researchers at NRC are developing a cesium fountain clock that has demonstrated higher precision, accuracy, and stability. When completed, it will be up to one hundred times more accurate than present clocks.