Roughly 6 million cargo containers are shipped to U.S. seaports each year and each container carries up to 30 tons of freight in varied configurations. Highly enriched uranium and other fissionable material concealed inside these containers present a significant challenge for existing monitoring systems, due in part to the attenuation of signals in the cargo and in the container's walls. There are a number of systems currently being developed to overcome these challenges without slowing the flow of commerce through the port while keeping the likelihood of false-negative and false-positive detections to a minimum.

Our research uses the γ-ray beam produced at the High Intensity γ-ray Source (HIγS) (see fig.1). This nearly mono-energetic and 100% polarized γ ray beam of intensity exceeding 107 γ/s allows us to perform three types of measurements on actinide nuclei:

1. search for low-spin states with excitation energies greater than 2 MeV;
2. energy spectra and angular distributions of prompt and delayed neutrons produced in photonuclear reactions;
3. high accuracy γ-ray attenuation coefficients in actinides in 3 to 50 MeV energy range.

These measurements are important for developing new technologies aimed at identifying signatures of fissile materials via photon interrogation. They also provide insight into nuclear spectroscopy of actinides.

We are also conducting simulations of the experimental signatures of special nuclear materials (SNM) and relevant detector responses.

This simulation project aims to:

1. develop a data base for the NRF signatures of the ~20 most common isotopes present in cargo containers;
2. use this data base to:
• simulate backgrounds relevant to the detection process of SNM;
• simulate the interaction of a γ-ray beam with the contents of a container;
• optimize detector placement for γ-ray beam characteristics such as energy resolution, polarization, time structure, etc. ;
• identify possible signatures of SNM and evaluate the ratio of signal to noise ratio.