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"National Institute of Standards and Technology"

Dr. Eric Benck


SPEAKER:Dr. Eric Benck
TITLE:Magnetic Levitation for the Dissemination of the Redefined Kilogram
The kilogram remains the last measurement unit in the SI to be defined by an artifact, the International Prototype Kilogram (IPK). The IPK is cylinder out of a platinum/iridium alloy which was made in 1879 and is kept by the International Bureau for Weights and Measures (BIPM) in a basement vault on the outskirts of Paris. Through comparisons with official copies made at the same time as the IPK, it appears that the IPK is losing mass compared to the copies. Although the change is quite small, the implication that the kilogram is changing over time due to some unknown mechanism is troubling. Consequently, a new definition of the kilogram will soon be adopted based on precise measurements of the Planck constant. This new definition of the kilogram will be done inside a vacuum, requiring a method to transfer the results to atmospheric pressure where most mass metrology is done. NIST is building a new mass calibration system where kilogram artifacts in both air and vacuum can be directly compared. This is done by using magnetic levitation to couple a mass suspended in air to a high precision vacuum mass comparator. The resulting measurements will not have to rely on theoretical adsorption models as do other methods of vacuum to air mass metrology. Details of the levitation technique, initial results, and plans for the ongoing construction of the magnetic levitation system will be presented.

Monday, November 4, 2013
MPHY 102, 10:00 a.m.
Hawking Auditorium

Department of Physics and Astronomy
Texas A&M University

Host: Dr. Hans Schuessler