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A Boltzmann Constant Determination Based on Johnson Noise Thermometry.

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Researchers measured the Boltzmann constant using an improved Johnson Noise Thermometry system. This electronic measurement achieved a relative standard uncertainty of 5.0×10⁻⁶, contributing to fundamental physics understanding.

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Area of Science:

  • Metrology
  • Thermodynamics
  • Fundamental Constants

Background:

  • The Boltzmann constant (k) is a fundamental constant relating temperature to energy.
  • Accurate determination of k is crucial for the redefinition of SI base units.
  • Previous measurements using Johnson Noise Thermometry (JNT) have provided valuable data.

Purpose of the Study:

  • To measure the Boltzmann constant using an improved JNT system at NIST.
  • To compare the new measurement with previous determinations and CODATA values.
  • To identify and mitigate sources of uncertainty in the JNT measurement.

Main Methods:

  • Utilized an improved Johnson Noise Thermometry (JNT) system at NIST.
  • Employed a novel input circuit and frequency response matching technique for noise sources.
  • Accumulated and integrated 49 days of cross-correlated noise measurement data.

Main Results:

  • Determined the Boltzmann constant k = 1.380 642 9(69)×10⁻²³ J/K.
  • Achieved a relative standard uncertainty of 5.0×10⁻⁶.
  • Observed a relative offset of -4.05×10⁻⁶ from the CODATA 2014 recommended value.

Conclusions:

  • The improved JNT system provides a precise measurement of the Boltzmann constant.
  • The main uncertainty contributions stem from statistical noise and frequency response variations.
  • This measurement refines the value of the Boltzmann constant and validates the JNT approach.