NIST researchers have made highly accurate measurements of the Boltzmann constant, a fundamental scientific value that relates energy to temperature. These measurements contribute to international efforts to redefine the kelvin, the unit of temperature in the International System of Units (SI). The new NIST results, which have a relative uncertainty of approximately 5 parts per million, are 2.5 times more accurate than previous measurements using the same technique.
The Boltzmann constant is currently defined using the triple point of water, but this method has limitations. By defining the kelvin in terms of the Boltzmann constant, scientists can avoid variations in uncertainty and use quantum-mechanical effects for more precise temperature measurements.
The NIST research team used a quantum voltage noise source (QVNS) to measure Johnson noise, the random motion of electrons in a resistor. This technique, known as Johnson Noise Thermometry (JNT), provides a fundamentally accurate voltage signal based on quantum mechanics. The researchers compared the QVNS signal to the voltage noise created by the electrons in the resistor to determine the Boltzmann constant.
The new measurements, which were made in NIST’s Boulder, Colorado, laboratory and in collaboration with the National Institute of Metrology in China, satisfy the requirements for redefining the kelvin. The results will be included in determining a new Boltzmann constant value, which could lead to better thermometers for industry, including those used in nuclear reactors.
Keywords: Thermometry, Johnson noise, Boltzmann constant
