J. Plomp

Spin-echo small angle neutron scattering in Delft

We describe two spin-echo instruments for neutron small angle scattering, which have been installed at the reactor institute in Delft. The first setup is using a monochromatic beam and magnetized foils as spin flippers, while the second uses resonant spin flippers in a pulsed neutron beam. The components that play an essential role for operation are described in some detail. Each setup has specific advantages in its range of spin-echo lengths that covers the range of correlation lengths that could be measured. This is demonstrated in a comparative measurement, the setup with magnetized foils measuring at spin-echo-lengths up to 20 μm and the setup with resonant flippers measuring in the range up to 0.5 μm.

Structural transitions of hard-sphere colloids studied by spin-echo small-angle neutron scattering

The structure of hard-sphere colloidal suspensions is measured at different concentrations using the recently developed spin-echo small-angle neutron scattering (SESANS) technique. It is shown that SESANS measures real-space correlations ranging from the size of a single particle for a dilute suspension to several particle diameters for a concentrated suspension, glass and crystalline state.

Phase-object approximation in small-angle neutron scattering experiments on silicon gratings

The phase-object approximation for neutron scattering based on a one-dimensional dynamic forward scattering theory is discussed and used to calculate the differential cross section of an object. It is shown that this approximation is valid in ultra-small-angle neutron scattering (USANS) and spin-echo small-angle neutron scattering (SESANS) experiments on silicon gratings. In the weak scattering limit, the phase-object approximation reduces to the kinematic or first Born approximation. The spatial coherence function is used to describe instrumental resolution effects. Measurements on three different instruments are in good agreement with calculation results. In the experiment with a time-of-flight SESANS instrument, the effect of Pendellosung with object size is observed.

TOF-SEMSANS—Time-of-flight spin-echo modulated small-angle neutron scattering

We report on measurements of spatial beam modulation of a polarized neutron beam induced by triangular precession regions in time-of-flight mode and the application of this novel technique spin-echo modulated small-angle neutron scattering (SEMSANS) to small-angle neutron scattering in the very small angle range. It is shown that this method can be implemented straight-forwardly in order to extend the accessible size range of structures to be investigated by SANS towards a microscopic scale by applying a divergent beam and measuring the real space correlation function. The novel approach of SEMSANS enables the application of sophisticated sample environment and measurements of magnetic samples (in contrast to the analogue method SESANS).

Larmor precession applications: magnetised foils as spin flippers in spin-echo SANS with varying wavelength

A new development in SESANS instrumentation will be discussed. Magnetised foils as π-flippers for neutron polarisation were discussed in previous papers as powerful tools for constructing a strong gradient in Larmor precession in some direction. Up to now, such foils could only be used with limited flipping power and only for monochromatic neutrons. In this paper, it will be shown that it is possible to use foils also as nearly perfect flippers and moreover that such foils can be used also for varying neutron wavelength.

Quantitative Neutron Dark-field Imaging through Spin-Echo Interferometry.

Neutron dark-field imaging constitutes a seminal progress in the field of neutron imaging as it combines real space resolution capability with information provided by one of the most significant neutron scattering techniques, namely small angle scattering. The success of structural characterizations bridging the gap between macroscopic and microscopic features has been enabled by the introduction of grating interferometers so far. The induced interference pattern, a spatial beam modulation, allows for mapping of small-angle scattering signals and hence addressing microstructures beyond direct spatial resolution of the imaging system with high efficiency. However, to date the quantification in the small angle scattering regime is severely limited by the monochromatic approach. To overcome such drawback we here introduce an alternative and more flexible method of interferometric beam modulation utilizing a spin-echo technique. This novel method facilitates straightforward quantitative dark-field neutron imaging, i.e. the required quantitative microstructural characterization combined with real space image resolution. For the first time quantitative microstructural reciprocal space information from small angle neutron scattering becomes available together with macroscopic image information creating the potential to quantify several orders of magnitude in structure sizes simultaneously.

Spin-echo small-angle neutron scattering to study particle aggregates

A new method to measure spin-echo small-angle neutron scattering using π-flipping magnetised foils has been realised. This method makes it possible to measure in real space structural feature up to length scales of 2.5 μm. Measurements on concentrated colloidal systems reveal directly the evidence for short-range ordering.

Advances in Neutron Reflectometry at ISIS

Neutron reflectometry is a well established technique for the study of nanometre scale layered systems which are of direct relevance to a broad range of disciplines cutting across the physical and life sciences [1,2,3]. The second target station (TS2) at ISIS [4] is optimised to produce a large flux of cold neutrons, which when coupled with the large wavelength bandwidth provided by the 10Hz repetition rate offers the possibility for a step change in capability for the study of nanoscale systems.

Polarization optimization of spin-echo small angle scattering instruments

The polarization optimization in a small angle scattering spin-echo setup is considered, under the depolarization and phase errors that occur in field transition regions by improper adjustment of inclined magnetized foils as pi-flippers. Various correction procedures are discussed. In these setups with precession fields perpendicular to the beam directions, corrections can be reduced strongly by the use of pi-flippers, and for the remaining errors, correction coils can be constructed.

Test of adiabatic spin flippers for application at pulsed neutron sources

Abstract Experimental results on the flipping efficiency are shown for a set of 2 V -coils as spin flipper and for a high-frequency flipper with adiabatic transition. The influence of the adiabaticity parameter is discussed. The merits of these adiabatic flippers are compared with the use of “monochromatic” flippers, when operated in a beam from a pulsed neutron source. It is concluded that for “long pulse” sources adiabatic flippers will be superior.