News Flash: Radiographic Imaging using Neutrons

News Flash: Radiographic Imaging using Neutrons (4th November 2009)

Under Small Business Innovation Research (SBIR) contracts with the National Science Foundation and the US Department of Energy, Adelphi Technology Inc. has developed new “eyes” for examining the interiors of objects using a compact laboratory neutron source and camera. Unlike x-ray imaging, neutrons can penetrate high density materials such as lead, steel and even uranium. High image contrast and high resolution can be achieved of lower density metals and hydrogen bearing materials (e.g. epoxies and plastics) when these are embedded into, or screened by, higher density materials. Both thermal and fast neutrons can be generated and used for imaging.

Similar to x-ray radiographic apparatus, there is a source of radiation, an object to be imaged and a camera which converts the neutron image into a computer graphic. Neutrons are produced in a safe fusion reaction contained in a steel-envelope tube. The neutrons are then collimated to illuminate only the object and camera, where the image is converted to an electronic one. The neutron camera is composed of a plastic scintillator imaged by a CCD optical camera. Neutrons impinge upon the scintillator, producing light which is imaged on the CCD camera. The Adelphi prototype system can give two fields of view (10-cm x 10-cm and 42-cm x 30-cm). Our measured resolution is 2 to 4 mm for a 10-cm thick object. All of the images were taken in times from 10 to 60 minutes. Neutron source diameter is approximately D = 3 cm and distance, L, to the object from the generator is 1.5 to 3 meters (L/D of 50 to 100). Image quality is expected to improve and imaging times are expected to fall with further improvement to the camera and reduced neutron-generating target size.

Neutron Radiography Image of half-full Wine Bottle imaged through a 1/2 inch of lead The entire imaging system (camera and neutron source) can be converted in order to image with thermal neutrons. For thermal neutron imaging, the fast neutron source is moderated with a polyethylene and graphite plug, and the camera is modified by inserting a thermal neutron sensitive phosphor. These changes can quickly and easily be done, transforming the fast neutron imaging system into a thermal one. Thus the imaging system can work at two different neutron-energy regimes: fast and thermal. Thermal neutrons from small reactors have been used for years to image aircraft parts and fluid flows (e.g. oil) in engines. Imaging of corrosion, sub-mm-scale cracks, cubic-mm voids and other structural defects in large surface area, low-density materials such as aluminum aircraft wings is possible.