High resolution neutron radiography with very compact and efficient neutron collimators

Abstract

The spatial resolution in neutron imaging is often limited by the neutron beam divergence, especially in experiments where the distance between the sample and the detector cannot be very small. Imaging of relatively large or extended objects or tomographic experiments, where samples have to be rotated, typically require several to tens of centimeters distance between the sample and the detector. Moreover, some neutron imaging techniques require placement of components between the sample and the detector, as in the case of magnetic field imaging with polarized neutrons. Compact and efficient policapillary collimators can be an attractive alternative to the conventionally used beam limiting aperture approach. The possible improvement of spatial resolution by a policapillary collimator is studied in experiments where beam divergence limits the quality of neutron transmission imaging. A ∼7 mm thick collimator with ∼6 µm capillaries demonstrates the possibility to decrease the neutron beam divergence and to diminish the image blurring. The improvement of out-of-angle neutron rejection and peak transmission of our future collimators will be crucial for their effective application in neutron imaging experiments.

Quantification of Cement Hydration through Neutron Radiography with Scatter Rejection

“…Collimators with larger areas, as well as with curved geometries for scattering experiments can be manufactured. These collimators do not introduce image distortions unless the spatial resolution reaches 10 m levels, as demonstrated previously [25], [26]. The glass composition of these collimators was modified to contain neutron absorbing Gd and B atoms.…”

Design of a novel compact neutron collimator

“…More recently, Stone et al [4] demonstrated the possibility of boron carbide and plastic compounds as effective materials for the building of neutron collimators. There are extensive studies regarding microchannel neutron collimators [5,6] reaching up to thousands of channels per square millimetre, but they suffer the drawback of a relatively high transmission index for uncollimated neutrons. In our approach, the designed collimator will implement a matrix of millimetre size transmission channels alternated to absorbing elements made of a mixture of polylactide and natural boron carbide, which will offer a very low transmission index for uncollimated neutrons.…”

Refraction contrast imaging and edge effects in neutron radiography

“…The compactness of novel neutron collimators with micropores of small diameter (6-10 µm) [17]- [19] enables their placement between the object and the detector without degradation of image quality due to the beam divergence, figure 6. It was already reported how these collimators can be used to improve quantification in experiments with scattering materials by removing the scattering component from the radiographic images [19]. The small pore size of these devices results in no observable distortions of the images unless the detection resolution is better than 10 µm.…”