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

At the high-flux reactor of the Institut Laue-Langevin in Grenoble, the quotient h/m(n) (h Planck constant, m(n) neutron mass) was measured with a relative uncertainty of 7,7 x 10(-8). According to the de Broglie equation, h/m, is equal to the product of the wavelength and the velocity of a free neutron. To obtain these quantities, a beam of neutrons with an identical and well-known wavelength was produced by Bragg reflection in a silicon crystal. The velocity of the neutrons was measured by a special time-of-flight method. The result is h/m(n) = 3,956 033 320 (302) x 10(-7) m(2)s(-1). From h/m(n) the value of the fine-structure constant alpha can be derived. The measured value leads to alpha(-1)=137,036 010 82(5 24) (relative uncertainty 3,9 x 10(-8)). This method of determining ct greatly differs from all methods used so fur.