Method and apparatus for detecting dilute concentrations of radioactive xenon in samples of xenon extracted from the atmosphere

A method for measuring the concentrations of multiple radioxenon isotopes in a gaseous sample of xenon, the method comprising:

• providing a detector comprising N sub-detectors surrounding a sample cell, wherein the N sub-detectors are sensitive to both electrons and photons from radioxenon decays, specifically including beta decays, conversion electrons, x-rays, and gamma-rays;
• providing a plurality of waveform digitizers for the N sub-detectors;
• introducing the sample of xenon into the sample cell;
• in response to detecting pulses from the N sub-detectors,
• digitizing the waveforms of the detected pulses from the N sub-detectors;
• and
• storing the digitized waveforms into a data file, along with an indication of which sub-detector produced each waveform, and a time stamp for each waveform;
• and
• at a later time, processing the digitized waveforms in the data file by,
• analyzing the digitized waveforms of the detected pulses,
• extracting the energies of one or more events per pulse,
• examining the timestamps of the other digitized waveforms in the data file to detect coincidences between sub-detectors,
• whenever a coincidence between two events is detected, recording the two events' two measured energies as a point in a two-dimensional histogram,
• whenever a coincidence between three events is detected, recording the three events' three measured energies as a point in a three-dimensional histogram, and
• establishing regions of interest (ROIs) within both the two-dimensional histogram and the three-dimensional histogram that correspond to decay paths of the multiple radioxenon isotopes to be measured, and
• computing estimates of the concentrations of the multiple radioxenon isotopes, based on the number of counts collected in each of the ROIs.

An apparatus for measuring the concentrations of multiple radioxenon isotopes in a gaseous sample of xenon, the apparatus comprising:

• a detector comprising N sub-detectors surrounding a sample cell, wherein the N sub-detectors are sensitive to both electrons and photons from radioxenon decays, specifically including beta decays, conversion electrons, x-rays, and gamma-rays;
• and
• signal processing electronics for the N sub-detectors, the signal processing electronics configured to:
• detect both single and coincident events within a single sub-detector,
• detect coincident events between multiple sub-detectors, and
• measure the detected events' respective energies;
• during the measurement of the sample of xenon in the sample cell,
• whenever a coincidence between two events is detected, record the two events' two measured energies as a point in a two-dimensional histogram, and
• whenever a coincidence between three events is detected, record the three events' three measured energies as a point in a three-dimensional histogram, and
• after the measurement is completed,
• determine the number of counts within a set of regions of interest (ROIs) established within both the two-dimensional histogram and the three-dimensional histogram that correspond to decay paths of the multiple radioxenon isotopes to be measured, and
• use the number of counts so determined to estimate the concentrations of the multiple radioxenon isotopes within the sample cell.