Experimental performance evaluation of a compton suppression system by an analysis of geological reference materials

Compton scattering is one of major sources inducing a high background when a gamma ray spectrum is acquired from a radioactive sample. The high background spectrum deteriorates the detection sensitivity for an analysis of the nuclide of interest. To improve the detection sensitivity by the reduction of the spectrum background, a Compton suppression system (CSS) applying an anti coincidence mode was developed and has been used for a neutron activation analysis. A Compton suppression system (CSS) was implemented for an instrumental neutron activation analysis (INAA) at an NAA laboratory of the Korea Atomic Energy Research Institute (KAERI) in 2009. The CSS consists of a high purity Ge (HPGe) detector and bismuth germinate (BGO) with electronic modules. An evaluation of the performance of the CSS was carried out based on the measurement of the gamma ray emitting source and the detectable nuclides created thorough neutron activation of biological reference materials. This study was executed to evaluate the performance of the CSS for geological standard reference materials (SRMs). Four geological SRMs produced by the National Institute of Standards and Technology (NIST) in the USA were selected and irradiated using an NAA 1 irradiation hole at HANARO. Gamma ray spectra with normal mode and anti coincidence mode were acquired at the same time, and advantage factors of CSS for each nuclide detected were calculated on the basis of the signal to noise ratio