Spin echo modulated small-angle neutron scattering using superconducting magnetic Wollaston prisms

Abstract

The spin echo modulated small‐angle neutron scattering technique has been implemented using two superconducting magnetic Wollaston prisms at a reactor neutron source. The density autocorrelation function measured for a test sample of colloidal silica in a suspension agrees with that obtained previously by other neutron scattering methods on an identically prepared sample. The reported apparatus has a number of advantages over competing technologies: it should allow larger length scales (up to several micrometres) to be probed; it has very small parasitic neutron scattering and attenuation; the magnetic fields within the device are highly uniform; and the neutron spin transport across the device boundaries is very efficient. To understand quantitatively the results of the reported experiment and to guide future instrument development, Monte Carlo simulations are presented, in which the evolution of the neutron polarization through the apparatus is based on magnetic field integrals obtained from finite‐element simulations of the various magnetic components. The Monte Carlo simulations indicate that the polarization losses observed in the experiments are a result of instrumental artifacts that can be easily corrected in future experiments.

High-resolution phonon energy shift measurements with the inelastic neutron spin echo technique

“…For an inelastic neutron spin echo experiment with a low signal, the key is to obtain the parameters precisely from the measured data points with sinusoidal oscillations, namely IðxÞ ¼ A sin ½ðx þ ÈÞ þ C. Here, C denotes the shim neutron intensity, which scales with the counting time, is the frequency of the oscillations, which is determined by the setup and neutron energy, x is the parameter of scanning, which is magnetic field intensity in this case, È is the phase of the oscillation and A is the amplitude of the oscillation. It is also helpful for us to understand how to perform the fit for other Larmor labeling techniques, like spin echo modulated smallangle neutron scattering (Li, Parnell, Bai et al, 2016) and spin echo small-angle neutron scattering (Parnell et al, 2015). So in the following section, for each point on a sinusoidal curve of [x, I(x)], a random number generator will be used to generate a number [x, I 0 (x)], where I 0 (x) follows a Poisson distribution, similar to a real neutron source.…”

New capabilities in high-resolution neutron Larmor diffraction at ORNL

“…For example, if the lattice distortion is large enough that some of the diffracted neutrons fall out of the detector or are cut off by the collimator after the sample, the setup is not performing a complete Fourier transform and we cannot get the correct answer. Therefore, Larmor diffraction is similar to other neutron Larmor labelling techniques (Parnell et al, 2015;Li, Parnell, Bai et al, 2016), in that all the scattered or diffracted neutrons need to be detected. From Bragg's law = 2d sin , to measure a lattice distortion of Ád/d for a lattice spacing of d, the minimum collimation after the analyser is Á = tan ()(Ád/d).…”

Small Angle Scattering in Neutron Imaging—A Review

“…Significant progress has been achieved recently with two techniques that allow much higher magnetic fields than the conventional wire wound coils. The first is the development of the superconducting magnetic Wollaston prisms [54] for spin-echo modulated SANS, which could easily be transferred to quantitative SEM-DFI. This setup in particular allows a very compact design.…”