Investigation of possible hydrogen shielding effect on epithermal neutron activation analysis - a computation and experimental approach

Neutron activation is a popular analytical technique used to determine the presence and concentration of certain elements. It has several variations, including thermal neutron, epithermal neutron, fast neutron activation, etc, for different applications; all of those variations are non-destructive, and sensitive to small quantity. While trying to determine the concentration of Cl and Br in the light water solution, Dr. Landsberger’s team found the epithermal neutron activation analysis results were 25% lower than the conventional chemical method. They were not able to determine the cause of such discrepancy. This study was motivated to re-examine such discrepancy, and to study its possible causes. Furthermore, the study tries to determine if such discrepancy, if it exists, was linked with thermal neutron cut off or hydrogen absorption of neutrons. A computer simulation using the Monte Carlo radiation transport software MCNPX was developed to radiate sample Cl & Br solutions of known mass concentrations in a simulated TRIGA reactor core at 500 KW steady state power. [1] The neutron activation rate of Br, Cl at each concentration was then calculated. Such procedure was then repeated for heavy water solutions. Finally, a cadmium shield was added to eliminate thermal neutrons; all samples were tested again using epithermal neutron activation. The actual neutron activation experiment was also carried out in the University of Texas’s TRIGA Mark II reactor. A total of 40 samples of Br & Cl solution (with and without Cd, in light water and in heavy water) were irradiated in the reactor at 500 KW steady state power.