In 1960, which isotope was used to define the standard measure of length?

Key Points

• Krypton-86 was used in 1960 to define the standard measure of length.
• The length of the meter was defined based on the wavelength of the radiation emitted by Krypton-86.
• This definition was adopted by the 11th General Conference on Weights and Measures (CGPM) in 1960.
• It was later replaced in 1983 by the definition based on the speed of light.
• The use of Krypton-86 provided a more precise and reproducible standard compared to the previous definitions.

Additional Information

• The General Conference on Weights and Measures (CGPM) is the international authority responsible for uniformity in measurements.
• In 1983, the meter was redefined as the distance light travels in a vacuum in 1/299,792,458 seconds.
• This new definition ties the unit of length directly to a fundamental constant of nature, the speed of light.
• The redefinition aimed to increase the precision and universality of the meter as a unit of measure.