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Making a noise about thermometry
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12/06/2008
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Researchers at the US National Institute of Standards and Technology (NIST) have built a system that relies on the noise created by electrons as a basis for measuring temperatures with extreme precision.
According to NIST, the system is nearly precise enough to help update some of the crucial underpinnings of science, including the 54year-old definition of the Kelvin, the international unit of temperature.
The NIST system measures electrical noise in resistors when they are cooled to the triple point of water (273.16 K), the temperature at which water’s solid, liquid and vapour forms coexist in balance. This so called ‘Johnson noise’ is directly proportional to temperature.
The Johnson noise thermometry (JNT) system is said to bring a fivefold improvement in noise thermometry, due to the use of a quantum voltage source. NIST also says the system is simpler and more compact than other approaches.
The JNT may also contribute to the determination of Boltzmann’s constant, which is likely to be redefined in a few years so that it is linked to fundamental constants.
The most accurate measurement of the Boltzmann constant to date was performed at NIST about two decades ago using acoustic gas thermometry. Although the JNT system would require further improvements to be competitive with the acoustic method, says NIST, this is thought possible. However, the JNT system is slow: it will take about one month to integrate the data to achieve the precision needed to define the Boltzmann constant.
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Author
Graham Pitcher
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