A pre-concentration neutron activation analysis method for the determination of 232Th utilizing a dry-tube irradiation facility

Abstract

A revized method for determining 232Th using a pre-concentration neutron activation analysis (PCNAA) procedure was developed to accommodate irradiation in a dry irradiation tube environment. 232Th extracted by ion-exchange from a sample was electrodeposited onto 5/8″ diameter vanadium planchets, which are arranged in a stack and irradiated in the dry tube central irradiation facility (CIF) of the reactor. The higher neutron fluence of this facility improved sensitivity by approximately 37%, however, the higher temperatures required modifications to the irradiation procedure. Because the heat in the CIF would melt the plastic spacers used in the original method, a tube of high-purity quartz was used to contain samples, and high purity quartz spacers were used to separate the vanadium planchets during the irradiation. Test irradiations have determined that no significant transfer occurred from the disks to the silica disks and no significant variation in the neutron flux was observed. Finally, a thin film barrier was tested for its ability to reduce recoil contamination from 229Th onto the detector during alpha spectroscopy. The film was shown to reduce contamination to levels indistinguishable from normal background.