High Purity Germanium Detection System For The In Vivo Measurement Of Americium And Plutonium PDF Download

The Defense Threat Reduction Agency (DTRA) contracted for two gamma radiation detectors: mercuric iodide (HgI2) and electromechanically cooled (EMC) high purity germanium (HPGe) to support arms control inspection efforts. This project investigated whether these detectors could measure the quality and quantity of special nuclear material (SNM), particularly Pu-239 for the treaty verification mission. The project investigated two areas of detector capabilities: 1) HgI2 and HPGe detector performance necessary to characterize the quality of plutonium and the presence of shielding materials and 2) HgI2 and EMC HPGe detector performance degradation by high noise levels and EMC HPGe detector performance degradation caused by electromechanical-cooling. The first area studied the response functions of each of the detectors necessary to meet the detection objectives: measure the Pu-239/Pu 240 ratio to identify weapons grade plutonium and to identify a phony weapon. The second area of detector performance evaluated was the EMC HPGe detector's cooling capabilities and its effect on the performance of the detector. The results show that neither of the detectors was ideally capable of supporting DTRA's requirements. The HgI2 detector did not have sufficient efficiency or resolution to distinguish between Weapon Grade and Reactor Grade Plutonium. The EMC system suffered from grounding problems that degraded the resolution and efficiency. An initial study, evaluating the ability of detectors to determine the presence of a simulated tamper within the SNM physics package, showed great promise for identifying phony weapons.