Recent developments in ultra low-level γ-ray spectrometry at IRMM

Abstract IRMM performs ultra low-level γ-ray spectrometry in the underground laboratory HADES, located at the SCK·CEN site in Mol, Belgium. Recently a third low-background coaxial HPGe detector was put into operation. The detector has 60% relative efficiency and better background characteristics than the two previous detectors. The shield comprises 14 cm of lead with 210 Pb specific activity of 20 Bq kg −1 and 14 cm of freshly produced electrolytic copper. The background count rate integrated from 40 to 2700 keV is 394 ± 2 counts per day. Details of the background and the shield are presented together with applications to nuclear safeguards and material selection.