Electronic stability and noise reduction in Doppler broadening spectroscopy systems

At the University of Hong Kong's positron beam two related positron defect spectroscopies are being developed, namely, positron deep level transient spectroscopy (PDLTS), and coincidence Doppler broadening spectroscopy. Both of these spectroscopies require the use of high purity Ge detectors and the standard high gain nuclear instrumentation amplifiers. In this paper we review some of the difficulties that we have encountered in making such measurements satisfactorily in one of the busiest cities of the world. Attempts, such as using battery power supply, opto-isolating from local mains, connecting to an independent ground and adding a spectrum stabilizer, have been made to overcome the noise problem. However, the results are not particularly promising. The reasons why are discussed. (C) 2002 Elsevier Science B.V. 2002 rights reserved.