Effect of anomalous absorption of neutrons undergoing Laue diffraction at Bragg angles close to $\pi/2$

A direct experimental observation of the anomalous absorption of neutrons undergoing Laue diffraction in a highly perfect silicon single crystal of size about $200$ mm at Bragg angles close to $\pi/2$ is reported. It is shown that, in the case of diffraction at the $(220)$ plane, the neutron absorption length may be several meters, which is nearly one order of magnitude longer than the mean absorption length for neutrons of the same wavelength. This circumstance makes it possible to study effects accompanying Laue diffraction at Bragg angles of up to $88^\circ$ and a crystal size of about $200$ mm.