1. 1 Current Compton Imaging Effort for Homeland Security at LLNL Address one of the outstanding problems for Homeland Security: “Faint” sources in the midst of background fluctuations Gamma-ray imaging to provide  Location and shape of nuclear materials  Increased sensitivity in the detection of nuclear materials (increase signal-to-background, distinguish threat sources from background fluctuations (spatially and temporarily) Compton imaging provides high sensitivity with large FOV (4  ) and w/o heavy collimators Cryogenically cooled, large-volume Si(Li) + HPGe detector in double-sided strip configuration provide high sensitivity throughout energy range of interest for DHS (180 keV – 2.6 MeV) Couple 4  Compton imager to 4  visual photo/video camera Provide 3D imaging either in near field or by moving source or detector 344 keV Imaging of extended 152 Eu source

2. 2 Current Compton Imaging effort for Homeland Security at LLNL Current Compact Compton Imager system consisting of 2 Si(Li) and 2 HPGe DSSDs 3D position determination by combining 2D segmentation and pulse-shape analysis 2D and 3D gamma-ray imaging Combining 3D gamma-ray and visual images (LIDAR mapping system) Si+Ge detectors Photo camera Dewar Pre- amplifiers 20 cm 2D gamma-ray + 3D visual images 3D gamma-ray + 3D visual images Example of signal shape fitting to deduce #, energies, and 3D position of interactions

3. 3 Proposal to DNDO/NSF 07-545 (Academic Research Initiative) to evaluate electron-tracking based Compton imaging Reduce cone to arc without loosing angular resolution Concept of Si-Drift Detectors

4. 4 Examples of measured electron tracks Position  Track  E/dx  Vertex (origin of track)  Complete vs. incomplete energy deposition  Particle identification?

5. 5 Opportunities for UC 1m 2 -scale gamma-ray and neutron detectors and imagers to detect faint sources Electron-tracking based imagers, e.g. LAr … Gamma-ray imaging … …. Connection to Biomedical Applications (10 th Campus UCSF…)