A well-type Ge(Li) detector for sum-coincidence studies

Abstract

The feasibility and usefulness of a coaxial Ge(Li) spectrometer as a well-type detector for sum spectra of coincident gamma rays is demonstrated. The value of the well-type geometry has previously been established in nuclear gamma spectroscopy with the use of NaI(Tl) detectors. In this work a 16 cm 3 hollow cylindrical germanium detector has been made and mounted in such a way that access to the center of the detector is achieved from outside the cryostat. The detector is a fully depleted structure in which a hole of 1 cm diameter was ultrasonically cut, and a non-injecting contact applied to the inside surface. The detection of sum lines arising from 2 or more coincident gamma rays is demonstrated by using the radioactive sources of 110mAg and 110mIn. With the source inside the well, for which the counting solid angle is nearly 4π, the sum peaks of two or three lines were observed with an energy resolution of 3.5 keV (fwhm). For the source outside the detector at a distance of 10 cm, these sum lines were not observed above background for comparable counting statistics. Although the efficiency of the Ge(Li) spectrometer is not as high as that of the NaI(Tl), it is shown that this limitation is more than offset by its superior resolution.