Physica B+C最新文献

Four different focusing effects in two-crystal systems are discussed. (i) Focusing of monochromatic radiation at the back face, (ii) a geometric focus of polychromatic radiation, (iii) pure-wavefield foci due to lenses between the crystal plates and (iv) effective-mass enhanced focusing inside crystals due to the action of inhomogeneous external forces. We present some new experimental results on these foci and point out their relevance for the development of novel neutron interferometry systems.

It is shown that if one accepts Einstein's postulate that energy-momentum is conserved in all individual microprocesses, the Grenoble experiments imply that individual neutrons are waves and particles simultaneously. If one rejects this postulate (and thus accepts Heisenberg's statement that they are only conserved statistically) new experiments are needed to settle the Bohr-Einstein controversy.

It is shown that a quantization with a linear one-to-one correspondence rule which results in a quantum theory with a joint coordinate-momentum probability density may be determined by a system of equations following from the equation of Schrödinger.

At JINR, Dubna, a new DIFRAN facility has been installed on a neutron guide at the IBR-2 pulsed reactor. Results of preliminary experiments including investigations of neutron diffraction on bent perfect crystals, wavelength-dependent Pendellösung oscillations, anomalous transmission in InSb single crystals and the first successful test of a new three-plate monolithic interferometer are reported.

Dynamical diffraction theory applicable to both elastic and inelastic interactions of neutrons with crystals is rederived from the time-dependent Schrödinger equation. The description of satellite reflections, neutron acoustic resonance as well as the time modulation of integrated reflecting power in the case of slowly vibrating crystals are then dealt with using appropriate simplifications of the fundamental equations. The predictions of the theory are confronted with existing experimental results.

Ultracold neutrons can be trapped in evacuated cavities, the “neutron bottles”, and also in inhomogeneous matter distributions where the index of refraction for the neutron wave varies significantly. We report an investigation of resonance states of the latter type. They were observed in stratified media composed of two different materials. Further, we report on interferometry (in space and/or time) as an important application of interference phenomena. Several schemes of interferometers for neutrons of very long wavelength have been proposed.

It is known and has been demonstrated experimentally that the sensitivity of an optical interferometer can be increased by injecting squeezed light into the unused port of the interferometer. Here it is demonstrated that the sensitivity of a fermion interferometer can also be enhanced provided the fermions in the input state are suitably correlated. An SU(2) formalism is introduced which allows one to concentrate on those quantum numbers of the input state which are of relevance to interferometer performance.

Whether a space-time event is observed or not, its physical nature will not depend on the inertial frame of reference used for its mathematical description. Hence one can produce a non-dispersive de Broglie wave packet whose center adds a localising function to the wave mechanical description of a particle. Once observed, the past history of this function will describe the track of the particle up to the observation. It is here shown that this packet turns the quantum mechanical description of a single particle from mathematical tool to understandable physical theory.

When a quantum mechanical system is transported adiabatically around a closed circuit in parameter space, the system will, in addition to the usual dynamical phase, pick up a “topological”phase which depends only on the geometric history of the system. This phase, which is named after Berry who predicted it in 1984, has a number of exciting properties. We have measured these phases in neutron spin-rotation in helical magnetic fields.

It is usually assumed that neutron optical phenomena are adequately described by a one-body Schrödinger equation containing a complex optical potential that is given by the average value of the Fermi pseudopotential. The main problem with this elementary approach is that it only includes the attenuation of the neutron wave function in the medium resulting from absorption, and neglects the often more important contribution to the attenuation from diffuse scattering which is also present in reality. The purpose of this paper is to show how the rigorous theory of dispersion overcomes the above problem by taking properly into account the local field effects and a correction to the scattering amplitude that are neglected in the elementary theory. The importance of the local field correction in some current measurements of neutron scattering lengths by neutron optical experiments is also indicated.