Precision measurement of single slit diffraction with very cold neutrons

We performed experiments on diffraction of very slow neutrons (20 angstrom wavelength) from a slit of 90-mu-m width. A careful comparison was made between the slit width measured by light optical methods and the slit width deduced from the neutron diffraction pattern. We get satisfactory agreement between both values - possible explanations of a discrepancy, which had appeared in former measurements, are discussed.