Comparison of tomographic systems for X-ray and thermal neutrons

In this work, tomographic images of the same object have been taken with 25 keV X-rays and thermal neutrons (E=0.025 eV) aiming to demonstrate that thermal neutron tomography in some cases is a complementary technique to the X-ray tomography, such as in the examination of hydrogen-bearing compounds wrapped in a metallic matrix for instance. The capability of the neutron to pass through metallic materials such as lead, stainless steel and aluminium, allows to inspect encapsulated plastic explosives and visualize their inner structure like density variations, voids and alien materials, which are important features for the quality control of the final product. To obtain the images, a 3rd generation tomographic system with a Position Sensitive Detector has been developed. For X-rays this proportional detector was provided with an 8cm long carbon window, and filled with Ar - CH4 under a pressure of 2 atm. The X-ray beam was supplied by an ampoule with a tungsten anode manufactured by IPRJ/UERJ. For neutron detection the carbon window has been replaced by aluminium, and the filling-gas by ³He enriched helium, acting simultaneously as neutron converter and ionization gas. The Argonauta reactor at the Instituto de Engenharia Nuclear / CNEN was used as neutron source and furnishes a thermal neutron flux of 4.5x10(5) n · cm-2 · s-1 at its main channel outlet, where the tomographic system was installed