Imaging of heterogeneous materials by prompt gamma-ray neutron activation analysis

We have used a Tomographic Gamma Scanner (TGS) to produce tomographic Promp t Gamma-Ray Neutron Activation Imaging of heterogeneous matrices [T.H. Pret tyman, R.J. Estep, G.A. Sheppard, Trans. Am. Nucl. Sec. 69 (1993) 183-184]. The TGS was modified by the addition of graphite reflectors that contain i sotopic neutron sources for sample interrogation. We are in the process of developing the analysis methodology necessary for a quantitative assay of l arge containers of heterogeneous material. This nondestructive analysis tec hnique can be used for material characterization and the determination of n eutron assay correction factors. The most difficult question to be answered is the determination of the source to sample coupling term. To assist in t he determination of the coupling term we have obtained images for a range o f samples that are very well characterized; such as, homogenous pseudo one- dimensional samples to three-dimensional heterogeneous samples. We then com pare the measurements to Monte Carlo N-particle calculations. For an accura te quantitative measurement it is also necessary to determine the sample ga mma-ray self attenuation at higher gamma-ray energies, namely pair producti on should be incorporated into the analysis codes. (C) 1999 Elsevier Scienc e B.V. All rights reserved.