Determination of the fine-structure constant by measuring the quotient of the Planck constant and the neutron mass

A beam of neutrons with an identical and well-known wavelength was produced by Bragg reflection in a perfect silicon crystal; the velocity of the neutrons was measured using a very precise time-of-flight method. According to the de Broglie equation, the product of these two quantities is equal to the quotient h/m/sub n/ (h Planck constant, m/sub n/ neutron mass). The result is h/m/sub n/=3 956 033 320(302)/spl times/10/sup 7/ m/sup 2/ s/sup -1/ (relative uncertainty: 7.7/spl times/10/sup -8/). From this value, a value of the fine-structure constant /spl alpha/ was derived, leading to /spl alpha//sup -1/=137 036 011 28(5 24) (relative uncertainty: 3.9/spl times/10/sup -8/). The experiment was carried out at the high-flux reactor of the Institut Laue-Langevin in Grenoble, France.<
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