FEASIBILITY OF NEUTRON-ACTIVATION METHODS FOR MEASUREMENT OF SODIUM AND ALUMINUM IN GREEN LIQUOR

The feasibility of neutron activation methods including prompt gamma-r ay neutron activation analysis (PGNAA), neutron activation analysis (N AA), and continuous neutron activation analysis (CNAA) has been invest igated for both the off-line and on-line continuous measurement of sod ium and aluminum in green liquor. It is found that in the measurement of sodium and aluminum dissolved in green liquor at the 11% and 5.5% l evels, respectively, one must also know the chlorine content to determ ine the average neutron flux for any method involving neutron activati on. Chlorine may be present in green liquor in amounts up to 0.5% whic h would significantly (as much as 10%) affect the average thermal neut ron flux in a sample. It was found that PGNAA is quite sensitive to ch lorine and somewhat to sodium, but very insensitive to aluminum. Howev er, NAA and CNAA are quite sensitive to aluminum, then sodium, but ver y insensitive to chlorine. The final proposed approaches for discrete samples and continuous samples are to use NAA and CNAA, respectively, with time lags incorporated between activation and detection to reduce the effect of the otherwise overly intense aluminum spectrum on the l ess intense sodium spectrum and use of a He-3 detector to monitor the average neutron flux (a function primarily of chlorine content) in the samples. Extensive experimental and benchmarked Monte Carlo simulatio ns are used to evaluate the feasibility of this approach. It appears t hat the approach is viable and will allow accurate (1% relative standa rd deviation for both sodium and aluminum) discrete sample or on-line continuous analysis of both sodium and aluminum in green liquor in rea sonable times (10-30 min) with a relatively small (15 mu g) Cf-252 sou rce. Prototype devices are planned for future development. (C) 1997 El sevier Science Ltd. All rights reserved.