Large-area Si(Li) orthogonal-strip detectors
Segmented lithium drifted silicon detectors are being developed for use in large Compton cameras and for medical imaging. We have successfully fabricated 3.5 mm thick crossed-strip detectors with active areas of 40 /spl times/ 40 mm/sup 2/ with a 2 mm strip pitch. These detectors utilize new contact technology consisting of a boron implanted p-type contact and an amorphous silicon (/spl alpha/-Si) n-type contact. Good energy resolution and excellent strip separation was obtained from both contacts at relatively high operating temperatures. An energy resolution of 2.1 keV FWHM at 122 keV was obtained for the /spl alpha/-Si strip at temperature up to 200 K and for the B strip at temperature up to 240 K. Measurements of the charge sharing between the strips were also performed. When the detector was flood illuminated with 60 keV gamma-rays, a small signal deficit was observed for events in which the signal was shared between two adjacent strips. The amount of deficit depended on the contact type, strip geometry and the operating temperature.
Leakage current in high-purity germanium detectors with amorphous semiconductor contacts
Abstract Amorphous semiconductor electrical contacts on high-purity Ge radiation detectors have become a valuable technology because they are simple to fabricate, result in thin dead layers, block both electron and hole injection, and can readily be finely segmented as needed for applications requiring imaging or particle tracking. Though significant numbers of detectors have been successfully produced for a variety of applications using the amorphous semiconductor contact technology, there remains a need to better understand the dependence of performance characteristics, particularly leakage current, on the fabrication process parameters so that the performance can be better optimized. To this end, we have performed a systematic study of leakage current on RF-sputter-deposited amorphous-Ge (a-Ge) and amorphous-Si (a-Si) contacts as a function of process and operational parameters including sputter gas pressure and composition, number of detector temperature cycles, and time spent at room temperature. The study focused primarily on the current resulting from electron injection at the contact. Significant findings from the study include that a-Si produces lower electron injection than a-Ge, the time the detector spends at room temperature rather than the number of temperature cycles experienced by the detector is the primary factor associated with leakage current change when the detector is warmed, and the time stability of the a-Ge contact depends on the sputter gas pressure with a higher pressure producing more stable characteristics.
New Approaches for Positron Emission Tomography ( PET ) in Breast Carcinoma
Positron Emission Tomography (PET) is a nuclear medicine imaging technique which allows the quantitative evaluation of the distribution of several pharmaceuticals in a target area. PET therefore provides valuable information on the biochemical and biological activity inside a living subject in a noninvasive way, combining techniques applied in nuclear medicine with the precise localization achieved by computerized image reconstruction.