Using Fallout Gamma Spectra to Identify Nuclear Device Characteristics at Short Times after the Event

摘要

Identification of device characteristics from nuclear fallout shortly after a low-yield nucleardetonation can provide important clues to nuclear forensics investigators. The gamma radiationemitted from this fallout possesses features that can be used to identify the materials used in theconstruction of the device as well as the type of reaction which powered the detonation.Building upon previous work by Monterial et al. [1], this work identifies characteristics of theshort time period gamma spectra emitted by fallout that can be used to determine whether thedevice was primarily powered by a ~(239)Pu or ~(235)U core and whether the detonation primarilyproduced a fission neutron spectrum or a high energy spectrum characteristic of fusion. TheDefense Land Fallout Interpretive Code (DELFIC) [2] was used to simulate fallout from a 10ktground burst of U and Pu devices at time periods of one day to one month after the event, whengamma ray characterization is expected to be conducted. These simulations were analyzed toidentify distinctive characteristics of each gamma spectra (U vs. Pu, fission vs. fusion) for use indevice identification. To check for possible sources of interference in the gamma spectra, ~(238)Ufission was also simulated and a detailed soil model was developed to check for the presence ofneutron activation products that may be present in the fallout.