Improvements of low-level radioxenon detection sensitivity by a state-of-the art coincidence setup

The ability to quantify isotopic ratios of 135, 133 m, 133 and 131 m radioxenon is essential for the verification of the Comprehensive Nuclear-Test Ban Treaty (CTBT). In order to improve detection limits, CEA has developed a new on-site setup using photon/electron coincidence (Le Petit et al., 2013. J. Radioanal. Nucl. Chem., DOI : 10.1007/s 10697-013-2525-8.). Alternatively, the electron detection cell equipped with large silicon chips (PIPS) can be used with HPGe detector for laboratory analysis purpose. This setup allows the measurement of β/γ coincidences for the detection of 133Xe and 135Xe; and K-shell Conversion Electrons (K-CE)/X-ray coincidences for the detection of 131mXe, 133mXe and 133Xe as well. Good energy resolution of 11 keV at 130 keV and low energy threshold of 29 keV for the electron detection were obtained. This provides direct discrimination between K-CE from 133Xe, 133mXe and 131mXe. Estimation of Minimum Detectable Activity (MDA) for 131mXe is in the order of 1 mBq over a 4 day measurement. An analysis of an environmental radioxenon sample using this method is shown. - Highlights: • A new electron/photon spectrometer for radioxenon measurements has been developed. • High resolution coincidence measurement of a 131mXe standard is presented. • A detection efficiency of 22±4 counts/s/kBq for 131mXe is obtained. • MDA of 0.9 mBq for 131mXe is obtained from a 3.9 day background measurement. • A complex environmental measurement is presented