A MONTE-CARLO STUDY OF THE INFLUENCE OF THE GEOMETRY ARRANGEMENTS ANDSTRUCTURAL-MATERIALS ON A PGNAA SYSTEM PERFORMANCE FOR CEMENT RAW-MATERIAL ANALYSIS

The MCNP-4A code, running on a Pentium PC, was used to simulate a conv eyor belt system for on-line cement raw material analysis, namely the determination of calcium, silicon, iron and aluminium contents. The in fluence of different system and sample parameters (overall system geom etry, neutron moderator/reflector composition and thickness, neutron a bsorber lining of detector shields, sample bulk density and water cont ent) on the background count rate originating from structural material s was studied. A configuration has been obtained which corresponds to a lower background due to structural materials and a relative higher c ontribution from gamma-rays produced in (n, gamma) reactions in the bu lk raw material. In this configuration, the dependence of the count ra te on the sample density and water content is different in the lower a nd upper detectors. In the upper detectors, the count rate from inelas tic reactions in lead surrounding the neutron source is shown to decre ase exponentially with increasing density values, thus enabling densit y measurements to be made. (C) 1997 Elsevier Science Ltd. All rights r eserved.