Semiclassical Computation Research Articles

Quantum calculation of vortex-induced torque

A rough quantum-mechanical calculation is given of the vortex-induced torque on a porous disk in rotating liquid helium II. The purpose of the calculation is both to serve as a check of the results of a recent semiclassical computation by Penney, and to illustrate some of the difficulties that might be encountered in a more rigorous derivation. Although the two approaches yield quite different formulas for the torque, both are (fortuitously) in agreement in magnitude, about a factor of 10 larger than the experimental results of Lynch and Pellam. It is pointed out that an experiment to decide between the two results might serve as a check on some aspects of the theory of quantum vortices.

Semiclassical crossing symmetry for semiclassical soliton scattering

Crossing symmetry (in a modified form) survives in semiclassical computations of relativistic particle scattering, and provides a nontrivial consistency test of such computations. The calculation of soliton scattering by Jackiw and Woo passes this test.

Quantum Mechanical Calculation of Neutron Stopping Power

The stopping power of matter is calculated quantum mechanically for the binding of atomic electrons is important) is shown to be insignificant at neutron energies of the order of 420/sup 0.35/ GeV or greater, where Z is the atomic number of the medium traversed. The quantum mechanical result shows a weaker dependence on neutron energy than an earlier semiclassical computation, applicable up to 10 GeV, although the two calculations give comparable numerical values in the range 5-10 GeV. A simple stopping-power formula is given for neutrons with form rtant. A more complicatd formula is given and evaluated numerically to 7000 GeV. The density effect and radiative corrections are not treated.

Semiclassical Calculations on Multiple-Quantum Transitions

It is shown that a recent quantum-electrodynamic derivation by Chang and Stehle of double-quantum resonance-frequency shifts is equivalent to a previously known semiclassical approximation, and that neither of these methods is adequate to account for the results of Kusch's experiments. A more-exact semiclassical computation is given, which is in reasonable agreement with Kusch's results in the region where these results are meaningful. It is concluded that the assertion of Chang and Stehle that quantum electrodynamics is necessary for such situations is unfounded.