Precision measurement of the bound-coherent-neutron scattering length of 235U.

With use of the neutron interferometric technique, the real parts of the bound-coherent scattering length, b, of /sup 235/U have been precisely measured for five different incident neutron energies in the range of 30 to 92 meV. The value of b at each incident neutron energy was obtained from the average of two independent measurements using two samples of different thicknesses. The results are b = 10.47 +- 0.04 fm (E = 30.34 meV), b = 10.47 +- 0.03 fm (E = 41.02 meV), b = 10.51 +- 0.03 fm (E = 51.43 meV), b = 10.39 +- 0.03 fm (E = 74.90 meV), b = 10.41 +- 0.03 fm (E = 91.39 meV). The uncertainty in these results is about an order of magnitude smaller than the present literature value. The small energy dependence of the observed scattering lengths has been used to establish the parameters of the negative energy resonance level (-1.4 eV) using the Breit-Wigner formalism.