DETERMINATION OF THE FINE-STRUCTURE CONSTANT BY A PRECISE MEASUREMENTOF H M(N) - THE FINAL RESULT/

At the high-flux reactor of the Institut Laue-Langevin in Grenoble (Fr ance), a beam of neutrons with a well-known wavelength was produced by Bragg reflection in a perfect silicon crystal; the velocity of these neutrons was measured using a very precise time-of-flight method. Acco rding to the de Broglie equation, the product of the wavelength and th e velocity is equal to h/m(n) (h Planck constant, m(n) neutron mass). From the value of h/m(n) determined in this way the value of the fine- structure constant alpha was derived. The results of a first series of measurements have already been published. The results of a second ser ies are now available. They are in excellent agreement with the previo us results. The final values following from all the experimental data of both series are h/m(n) = 3.956 033 332 (290) x 10(-7) m(2)s(-1) (re lative uncertainty 7.34 x 10(-8)) and alpha(-1) = 137.036 010 62 (503) (relative uncertainty 3.67 x 10(-8)), the uncertainties being one-sta ndard-deviation estimates.