Prompt gamma neutron activation analysis in borehole logging and industrial process control

Elemental analysis by prompt neutron activation analysis can be made by measuring the energy and intensity of prompt gamma-rays (PGNAA) emitted by an element upon capture of either a thermal or an epithermal neutron. Both prompt gamma-ray methods have a significant potential in bulk analysis because both neutrons and gamma-ray radiation are not significantly attenuated by the sample. The lack of absorption minimizes matrix effects and a large statistically meaningful sample is involved in the analysis. To accomplish the prompt neutron activation analysis in the laboratory it is relatively easy to design and control the entire process. The geometry of measurements is always constant and neutron flux at the sample can be measured. There is practically no restriction on size of detector or neutron source. However, in the narrow confines of a borehole there are a number of restrictions which must be considered. On-line analyses, although not restricted by space, have special problems in biological shielding, timing of detector pulses, need for rapid analysis and sensitivity for a given element. The purpose of this report is to discuss the different features which have to be taken into account when designing a PGNAA analyzer for a borehole logging tool or nuclear process control instrument. The performance characteristics of existing instruments, the special problems, possible solutions and the direction of the current thinking for future research are discussed. In addition, some appropriate applications where these instruments can be beneficially used to solve on-going problems are outlined. Refs, figs, tabs