NIST DEVELOPS NEW FORM OF NEUTRON RADIOGRAPHY PROVIDING FINE INTERNAL DETAILS.

Physicists from NIST and the University of Melbourne, Australia, have recently demonstrated for the first time a novel neutron phase-contrast imaging technique without the usual requirement of an interferometer. This form of phase-contrast imaging uses the transverse coherence properties of a neutron wave to enhance images, particularly of boundaries and edges. This technique is different from conventional neutron radiography where only the bulk features of a sample are visualized. The results of this research have been published recently in the journal Nature.

The experiments were performed at the NIST Center for Neutron Research, using a position-sensitive two-dimensional Charged Coupled Device neutron detector with nominal resolution of about 50 [micro]m. A lead bullet and a common wasp were chosen as specimens because these are representative of difficult cases for radiography by traditional methods with either x rays or neutrons.

One of the most important aspects of these experiments is that the researchers were able to extract the quantitative phase values, as well as the phase-contrast images. These phase values are critical to the interpretation of the images obtained. This phase extraction is possible by the application of the so-called paraxial "Transport of Intensity Equation" (TIE) to the image intensity profiles, which allowed the researchers to employ a simple, robust experimental setup without the need for stringent environmental control required in a typical interferometry experiment.

These experiments open the exciting possibility of investigating very fine structural details such as fractures and strain in commonly used industrial components, magnetic domains, and thin film-substrate interface boundaries. Further experiments are planned in the near future using polarized neutrons and magnetic samples.