MCNP(TM) SIMULATIONS FOR IDENTIFYING ENVIRONMENTAL CONTAMINANTS USINGPROMPT GAMMA-RAYS FROM THERMAL-NEUTRON CAPTURE REACTIONS

The primary purpose of the Multispectral Neutron Logging (MSN) project was to assess the effectiveness of existing neutron-induced spectral gamma-ray logging techniques for identifying environmental contaminant s along boreholes, to further improve the technology, and to transfer that technology to industry (Conaway and Frankle, 1993). The logging i nstrument incorporated a pulsed 14 MeV neutron source and HPGe detecto r. Gamma-ray spectra from thermal neutron capture reactions were used to identify contaminants in the borehole environment. This type of tec hnique complements physical sampling and is useful in environmental re storation projects where characterization of contaminated sites is req uired and long-term monitoring may be needed. We used an enhanced vers ion of the Monte Carlo N-Particle computer code (MCNP(TM)) to investig ate many more potential contaminants than could be accomplished experi mentally. MCNP was tested and benchmarked with experimental data for C l provided by our collaborators (Myers, 1988; Frankle, 1994) and exper imental data for Cl, Cd, Sm, Gd and Hg obtained as part of this projec t (Conaway and Duray, 1994). A number of enhancements were developed f or MCNP as a result of this project, some of which will be part of the next major code release. The results from the benchmarking effort, es timates of minimum detection thresholds for our instrument based on MC NP simulations, and some of the MCNP code enhancements will be discuss ed. Published by Elsevier Science Ltd.