PNNL Review of Proposed Relevant Radionuclide List

A list of fission products and activation products has been proposed for possible adoption as an official table of relevant isotopes for CTBT use. It is our understanding that the purpose of this list is to discriminate Level 4 spectra from Level 5 spectra in the decision logic diagram. The current understanding is that a single short-lived, relevant isotope that is atypical for a station would cause a spectrum to be marked as Level 4. A second relevant isotope would cause a spectrum to be marked as Level 5, which would perhaps require a sample to undergo additional laboratory conflation measurements. The list consists of a very comprehensive set of fission products and activation products. We have examined the list for accuracy and have also flagged potential problems with members of the list. in our opinion, several of these isotopes have serious problems and many have no practical chance of ever being the first or second detected isotopes. We are not arguing whether or not these isotopes might be seen in a large atmospheric test. On the other hand, there may be no harm associated with having a long list. The issue of activation products is different. Some activation products are indicative of the soil or rock composition in the vicinity of an explosion. Others may only be dependent on materials in the weapon or in the support structures. We don't think that a great deal of analysis of these isotopes by the CTBTO should be encouraged. In any case, if particulate activation products are in the atmosphere, fission products should be even more prevalent, thus removing the need for an activation list component