Scattering Of Slow Neutrons Research Articles

Formation of a Diffraction Field During Dynamic Scattering of Slow Neutrons in a Deformed Crystal

The problem of diffraction of slow neutrons with a de Broglie wavelength λ ~10-10 m in a crystal with a deformed lattice is considered. Based on the Hamilton equations describing the dynamic diffraction of slow neutrons, the features of the formation of a dynamic diffraction field in a lattice in various regions of the deformation field characteristics, including weak fields, slowly changing fields and rapidly changing fields are discussed. Using a particular example of a deformation field with a displacement field quadratic in coordinates, analytical solutions are obtained for the wave functions of transmitted and reflected lattice waves.

Scattering of slow twisted neutrons by ortho- and parahydrogen

The scattering of twisted Bessel neutrons from macroscopic and mesoscopic targets of ortho- and parahydrogen is studied theoretically. Superposition of twisted Bessel states is also examined. The angular distributions differ significantly from those for plane-wave neutrons with dependence on the twisted-neutron opening angle; a superposition of twisted Bessel states reveals an additional sensitivity to the orbital angular momentum projection. For mesoscopic targets, sensitivity to target location and the beam's orbital angular momentum depends on the relative sizes of target and beam parameters. These results suggest that scattering from molecular hydrogen may provide a means to characterize twisted-neutron beams.

Scattering of slow neutrons from long-wavelength magnetic fluctuations in UPt3

We report the observation of a low-energy contribution to the cross section of scattering of slow neutrons near the forward direction in the normal state of UPt3 at low temperatures. The results point to the existence of a weak component in the imaginary part of the dynamical wavevector-dependent susceptibility which may be represented approximately in a one-pole model with a wavevector-dependent relaxation frequency Gamma (q). In the low-q range of the measurements, Gamma (q) is up to an order of magnitude lower than the nearly q-independent characteristic frequency of a previously studied and well established dominant component of the dynamical susceptibility. The new low-frequency contribution is interpreted in terms of the effect of low-lying fermion quasi-particles in the presence of strong spin-orbit coupling.

Scattering of slow neutrons by bound nuclei

TheT-operator for scattering of slow neutrons by a system of bound nuclei is calculated up to quadratic terms in the scattering length. Binding effects as well as effects of multiple scattering have to be included in order to avoid inconsistencies. For the discussion of binding effects one can adopt methods developed by Dietze and Nowak [1] for treating scattering by an elastically bound nucleus. In particular the case of coherent elastic scattering is discussed: we show how the corrections can be expressed in terms of correlation functions and that binding effects are most important for scattering by light nuclei.

Scattering of slow neutrons by arsenic and selenium isotopes

Coherent neutron scattering lengths and free cross sections were measured for arsenic, for ordinary selenium and its isolated isotopes. By means of the Cristiansen filter technique the following scattering lengths for the bound atoms were obtained (in fm):b(As) =6.58(1) [b+=6.04(5) andb−=7.47(8)],b(Se)=7.970(9),b(76Se)=12.2(1),b(77Se) =08.25(8),b(78Se)=8.24(9),b(80Se)=7.48(3) andb(82Se)=6.34(8). Transmission measurements with neutrons of 1.26 eV and 5.19 eV resulted in an energy independent free scattering cross section for arsenic ofσs, t=5.40(3)b (in the eV-region).

Direct Measurement of the Spin-Dependent Capture and Scattering of Slow Neutrons byLi6

The spin-dependent capture cross section ${{\ensuremath{\sigma}}_{+}}^{c}\ensuremath{-}{{\ensuremath{\sigma}}_{\ensuremath{-}}}^{c}$ of slow neutrons ($\ensuremath{\lambda}=1.074$ \AA{}) by $^{6}\mathrm{Li}$ has been determined from the flipping ratio of a transmitted polarized neutron beam as a function of $^{6}\mathrm{Li}$ polarization. We used two methods, one of which also enabled us to measure the spin-dependent scattering length ${b}_{+}\ensuremath{-}{b}_{\ensuremath{-}}$ of $^{6}\mathrm{Li}$. We find ${{\ensuremath{\sigma}}_{+}}^{c}\ensuremath{-}{{\ensuremath{\sigma}}_{\ensuremath{-}}}^{c}=\ensuremath{-}1170\ifmmode\pm\else\textpm\fi{}50$ b and ${b}_{+}\ensuremath{-}{b}_{\ensuremath{-}}=(\ensuremath{-}0.38\ifmmode\pm\else\textpm\fi{}0.05)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ cm.

Scattering of slow neutrons by the isotopes of chlorine

The Christiansen-filter technique was used to measure the coherent scattering lengthsb for the bound atoms of the chlorine isotopes35C1 and37Cl. The results areb(Cl-35)=11.70 ±0.09 fm/atom andb(Cl-37)=3.08±0.06 fm/atom. Furthermore, the total cross section of natural chlorine for neutron energies 1.2 eV and 5.2 eV was determined by means of transmission measurements with rotating resonance detectors. From these data the spin state scattering lengthsa +(J=2) anda −(J=1) were obtained for the free nuclei of the isotopes. The derived values of the spin- and isotopically incoherent scattering cross section and the total scattering cross section at “zero energy” are well consistent with previously published resonance data. The present results combined with the resonance parameters make possible a complete description of the interaction of slow neutrons with the chlorine nuclei.

Multiple Scattering of Slow Neutrons by Statistical Media

A general expression for scattering cross section of slow neutrons by statistical media which includes all corrections from the multiple scattering is proposed. In place of the usual Van Hove scattering function, a general one is deduced. For a system composed of N non-interacting identical nuclei, it is represented in a form of the Van Hove scattering function S(q, w) multiplied by a constant factor independent of q and w, under some approximations. The numerical estimation of the constant factor is carried out.

Defecton Effects in the Scattering of Slow Neutrons

Defecton Effects in the Scattering of Slow Neutrons

Slow Neutron Scattering Form Factor from One-Dimensional Rotor

Slow Neutron Scattering Form Factor from One-Dimensional Rotor

Slow Neutron Scattering Form Factor from One-Dimensional Rotor

Slow Neutron Scattering Form Factor from One-Dimensional Rotor

Spin Correlation Effect on the Slow Neutron Scattering by Polyatomic Molecules with Particular Reference to Methane

Spin Correlation Effect on the Slow Neutron Scattering by Polyatomic Molecules with Particular Reference to Methane

Slow-Neutron Scattering by a Standing Electromagnetic Wave

We examine the elastic scattering of slow neutrons by a standing electromagnetic wave. It is shown that the real part of the coherent scattering amplitude arises essentially from the interaction of the induced electric dipole moment in the neutron with the electric field of the wave. The imaginary part of the coherent scattering amplitude arises from the interference between the magnetic dipole and spin-orbit interaction terms.

Rotational Molecular Motion and the Transient Nature of Liquids as Seen by Slow-Neutron Scattering

The analysis of neutron spectra scattered from molecular solids and liquids presents a formidable problem which so far has been only slightly touched upon. For a period of ten years, the translational motions of atoms in monatomic liquids have been investigated by neutron spectroscopists; their theoretical interpretation has reached a certain degree of refinement. An understanding of the effects of rotational motions on the neutron spectra scattered from molecular liquids, however, has not been developed to the same degree. The aim of the present work is to use some simple but reasonable model for the translational motions and to investigate in more detail the effect of the various possible rotational motions on the observed neutron spectrum. The general principle used is that translational and rotational motions are statistically uncorrelated. Thus, when the molecule as a whole vibrates and diffuses, it is assumed that it can also perform librations, free rotations, or rotational diffusion. Phonon expansions are done for the molecular vibrations and librations. Sears's basic theory is used to describe the free rotations and rotational diffusion. A cross section is obtained which contains all the basic components in the scattered-neutron spectrum. A discussion of good- and bad-resolution measurements is carried through. The value of older neutron-linewidth determinations is discussed. It is concluded that the resolution width ought to be \ensuremath{\le} 0.1 \ifmmode\times\else\texttimes\fi{} (the width of the rotational spectrum) if finer details of the rotational motion should be observed as resolved structure. With the aid of good-resolution data it is shown that the nature of the rotational motion changes drastically over the liquid range, from librations to almost free rotations. Comparison is made to changes of rotational motion of ions in the phase transition from the ferro- to the para-electric phase in the solid state. It is shown that from such observations of molecular motion the liquid appears as a phase transition or as a transient phenomenon.

Slow-Neutron Scattering by Light and Heavy Water

Since the model in which the water molecules form partially “ice-like” clusters explains the thermodynamic properties, the so-called itinerant oscillator model is applied to the motion of water molecules. The assumption is made that the atoms in a molecule receive stochastic forces from the neighboring molecules. The model of water with the stochastic force, of which the correlation functions are a delta function and a simple exponential, is discussed.The generalized frequency distributions of light and heavy water are derived from the model. The incoherent calculations of scattering laws of light and heavy water are compared with measurements. The model predicts well the total scattering cross section of light water, but the average cosine of scattering angle is slightly higher than that of the experiment. Further refinements in the model are discussed.

Slow Neutron Scattering and Classical Mean-Square Displacement Functions of Atoms

Slow Neutron Scattering and Classical Mean-Square Displacement Functions of Atoms

Rotational Molecular Motion and the Transient Nature of Liquids as Seen by Slow-Neutron Scattering

The analysis of neutron spectra scattered from molecular solids and liquids presents a formidable problem which so far has been only slightly touched upon. For a period of ten years, the translational motions of atoms in monatomic liquids have been investigated by neutron spectroscopists; their theoretical interpretation has reached a certain degree of refinement. An understanding of the effects of rotational motions on the neutron spectra scattered from molecular liquids, however, has not been developed to the same degree. The aim of the present work is to use some simple but reasonable model for the translational motions and to investigate in more detail the effect of the various possible rotational motions on the observed neutron spectrum. The general principle used is that translational and rotational motions are statistically uncorrelated. Thus, when the molecule as a whole vibrates and diffuses, it is assumed that it can also perform librations, free rotations, or rotational diffusion. Phonon expansions are done for the molecular vibrations and librations. Sears's basic theory is used to describe the free rotations and rotational diffusion. A cross section is obtained which contains all the basic components in the scattered-neutron spectrum. A discussion of "good"- and "bad"-resolution measurements is carried through. The value of older neutron-linewidth determinations is discussed. It is concluded that the resolution width ought to be \ensuremath{\le} 0.1 \ifmmode\times\else\texttimes\fi{} (the width of the rotational spectrum) if finer details of the rotational motion should be observed as resolved structure. With the aid of good-resolution data it is shown that the nature of the rotational motion changes drastically over the liquid range, from librations to almost free rotations. Comparison is made to changes of rotational motion of ions in the phase transition from the ferro- to the para-electric phase in the solid state. It is shown that from such observations of molecular motion the liquid appears as a phase transition or as a transient phenomenon.

Slow Neutron Scattering and Classical Mean-Square Displacement Functions of Atoms

Slow Neutron Scattering and Classical Mean-Square Displacement Functions of Atoms

A Slow Neutron Scattering Routine from the Gas Model

A Slow Neutron Scattering Routine from the Gas Model

Diamagnetic Scattering of Slow Neutrons

Diamagnetic Scattering of Slow Neutrons