Time resolved spectroscopy of cosmic-ray muons induced background

Abstract

The appropriate selection of a coincidence time interval in low-background experiments that are based on the rejection of anticoincidence background events is very important for reducing the influence of cosmic-ray muons on acquired spectral data, especially on certain energy regions of the obtained spectra. In an experiment that was performed by the coincidence system of an HPGe detector and a plastic detector in a surface laboratory, where the cosmic-ray muon flux is much higher than it would be in the conditions found deep underground (thus, better statistics in the acquired data are provided), the time resolution of the detected events is explored. We found that the prompt and delayed coincidence events between a plastic veto detector and a Ge detector can be sharply divided for approximately 100 ns in two groups. In addition, the bremsstrahlung and annihilation events can be time-resolved from the (n, n′) events, although all of these events belong to the group of delayed events. We also detected substantially delayed annihilation events, which are caused by the decays of stopped positive muons. © 2012 Elsevier B.V. All rights reserved.