Development of germanium strip detectors for environmental remediation

We present the initial results of the first germanium strip detector array for the imaging and high-resolution spectroscopy of gamma -ray sources. The array consists of four detectors, 5 x 5 x 1 cm each with 25 strips on each side. The detectors are daisy-chained to hybrid preamplifiers to reduce the number of channels of electronics. Good spectroscopy and imaging are achieved. We also present results from the development of an amorphous germanium contact technology as an alternative to the lithium contact technology. A prototype 25 by 25 strip detector was manufactured with this new technology and demonstrates good spectroscopy and imaging. High resolution, position-sensitive germanium detectors offer excellent capabilities for the detection, identification and characterization of radioactive isotopes. These detectors provide enhanced capabilities over existing systems and have direct applicability in the areas of Decontaminati on and Decommissioning (D&D), Nuclear Materials, Spent Nuclear Fuel (SNF), Mixed Waste, as well as for basic laboratory nuclear physics and gamma ray astrophysics. Germanium strip detectors are made by segmenting the contacts of a planar germanium detector. The two-dimensional information is gained by segmenting orthogonally on each side of the detector. One dimension is determined by which strip is collecting the electrons and the other dimension by the strip collecting the holes. The energy measurement is obtained from the amplitude of either the electron or the hole signal. These detectors can be used to create images of radioactive sources by placing them behind collimators or coded apertures. They can also be used in Compton cameras. The preferred method is dependent on the application: the source energy, dimension and intensity guide the choice of aperture. Intense sources can be heavily collimated but not weak ones. Diffuse sources are not well imaged with coded apertures but point sources are. High energy sources (> 1 MeV) are better imaged with a Compton camera because of the difficulty in making opaque masks or collimators at these energies.