ИСТИНА

The concept of group delay time (GDT) was introduced into the theory by D. Bohm and E.P. Wigner as a measure of time shift of a wave packet interacting with a stationary potential structure. It was widely used in the analysis of a number of quantum problems, at the same time playing the role of some sort of “theoretical clock". Later on, A.I. Baz proposed to measure the time of scattering by the potential of a particle with a magnetic moment, calculating the precession angle in a magnetic field presets in the potential region. Subsequently, it became clear that neutron experiments enabled implementation of the Larmor clock based on the constant precession frequency, and the Larmor time measured by it was closely related to the GDT. In the case of neutron reflection from resonant multilayer structures, the GDT can be much longer than in the case of total reflection. More-over, under certain circumstances, it can be negative. The latter can also be measured by the Larmor clock method. In addition, the GDT concept has proved useful for clarifying new aspects of neutron wave propagation in a refractive matter.