Neutron Imaging at Spallation Neutron Sources

Neutron imaging is a powerful method for non-destructive investigations where the high penetration through metals and the high contrast for hydrogenous materials is exploited in particular. The complementary to X-ray studies is a clever alternative in many cases of scientific and industrial applications. Reactor based neutron sources are becoming less available, caused by the shutdown of aged facilities. Accelerator driven neutron sources, in particular spallation sources, can provide similar performance also for imaging now, when digital imaging systems are utilized. The article shows the properties of imaging beam lines at SINQ, the presently strongest stationary spallation source. They deliver thermal neutrons as well as cold ones. Several beam line properties as collimation, field-of-view, neutron energy and spatial resolution can be changed and adapted to the conditions of the various experiments. The imaging methods include simple transmission radiography, timedependent studies, but also advanced methods like tomography and refraction enhancement. New aspects as quantitative tomography, phase contrast imaging and imaging with polarized neutrons are under consideration and implementation. A new and challenging aspect will be the use of the pulse structure of newly available large spallation sources like SNS, JPARC or ISIS-TS2 for imaging purposes. Despite the high peak intensity, which can be used for the study of fast repetitive processes, a time-of-flight imaging approach will enable energy resolved investigations. This is of particular interest at the Bragg edges of structural materials, where textural changes (e.g. near welds) become directly visible. First data of such kind of investigations can underline the importance of the new methodical approach.