Measuring low activities of fission-product xenon isotopes using the β-γ coincidence method

Ay-spectrometer facility operating in the beta-gamma coincidence mode is able to detect ultralow activities of Xe-131m, Xe-133m, Xe-133, and Xe-135 isotopes. A gas sample is introduced into the measuring chamber that is a thin-walled aluminum cylinder with its inner surface coated with organic scintillator to detect P particles and conversion electrons. The chamber is placed in the well of a Nal(TI) crystal detector of X and gamma rays, The resultant gamma-ray spectrum is formed by extracting X- and gamma-ray pulses coincident in time with pulses of beta particles and conversion electrons. The radiation background level is thereby reduced by two orders of magnitude in comparison with measurements in the standard mode (without coincidences), which leads to a significant increase in the spectrometer sensitivity. The design for the measuring, system used in the APNKC-01 complex of equipment is described, along with the determination of its efficiency and its energy calibration. Data on the sensitivity achieved are presented.