Preparation of Large Volume Planar Germanium Detectors and Results of Their Use in Nuclear Physics Experiments

Improved performance of germanium detectors, prepared by use of lithium-drift techniques, was obtained by means of measurements of diode properties and surface resistivity during preparation. A compensated thickness of 16 mm was obtained for several detectors in a single drift operation. For these and other detectors the provision of a negligible (i.e. < 10¿) dead layer on one side allowed the detector to be useful from 10 keV to 10 MeV. An electric field intensity of 50 to 175 volts/mm was sufficient to give satisfactory energy resolution (i.e., 3.0 - 4.5 keV @ 1.333 MeV) and full counting efficiency for detectors of thickness up to 16 mm. The preparation of 2 - 3 cm thick detectors by use of a dual-drift procedure, wherein two adjacent diode structures are caused to merge, is described. The joint use of coaxial and planar techniques, and their relative advantages, are discussed. It is concluded that the preparation of germanium detectors of area 25 cm2 and thickness 1.5 - 3.0 cm is feasible with present techniques, but limited by the quality of the crystals utilized. The results of application of these detectors to muonic x-ray studies, neutron-capture gamma-ray experiments, charged-particle induced reactions involving gamma rays, and isotopic analysis of materials such as uranium are presented. An advantage of a reduction in sensitive volume for some measurements at energies in the range 5 - 10 MeV is shown.