Novel energy-selective method for spectral correction in fast neutron computer tomography

The method is based on the concept of recording the spectral shifting in the pulse height spectrum in addition to the integral counting rate and to correct it depend on this shifting. The source used emits neutron- and gamma-ray, therefore a correction scheme which corrects the projection values for both types of radiation must be considered. In order to investigate the effects of spectral shifting and to develop the new correction method a program system including Monte-Carlo, numerical and analytical codes was implemented, which allows the simulation of single transmissions and even a whole set of projection values for reconstruction of CT-images. On the hardware side, the coupling of a spectroscopic and a neutron/gamma discrimination unit make the experimental determination of the shifting in the separated neutron- and gamma spectrum and the subsequent processing of the transmission values possible. By comparing CT-images reconstructed from spectral corrected and uncorrected projection values for both simulated and measured data, the applicability of the new spectral correction method is demonstrated. This is true for homogenous and inhomogenous test objects. The method has also been applied for the first time to objects having non uniform density. (orig.)