Progress on a method of barium tagging for the nEXO double beta decay experiment is reported. Absorption and emission spectra for deposits of barium atoms and ions in solid xenon matrices are presented. Excitation spectra for prominent emission lines, temperature dependence and bleaching of the fluorescence reveal the existence of different matrix sites. A regular series of sharp lines observed in Ba + deposits is identified with some type of barium hydride molecule. Lower limits for the fluorescence quantum efficiency of the principal Ba emission transition are reported. Under current conditions, an image of ≤ 10 4 Ba atoms can be obtained. Prospects for imaging single Ba atoms in solid xenon are discussed.

We describe a system to transport and identify barium ions produced in liquid xenon, as part of R&D towards the second phase of a double beta decay experiment, nEXO. The goal is to identify the Ba ion resulting from an extremely rare nuclear decay of the isotope 136 Xe, hence providing a confirmation of the occurrence of the decay. This is achieved through Resonance Ionization Spectroscopy (RIS). In the test setup described here, Ba ions can be produced in liquid xenon or vacuum and collected on a clean substrate. This substrate is then removed to an analysis chamber under vacuum, where laser-induced thermal desorption and RIS are used with time-of-flight (TOF) mass spectroscopy for positive identification of the barium decay product.

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The nickel-base alloy is one of the leading candidate materials for generation IV nuclear reactor pressure vessel. To evaluate its stability of helium damage and retention, helium ions with different energy of 80 keV and 180 keV were introduced by ion implantation to a certain dose (peak displacement damage 1–10 dpa). Then thermal desorption spectroscopy (TDS) of helium atoms was performed to discuss the helium desorption characteristic and trapping sites. The desorption peaks shift to a lower temperature with increasing dpa for both 80 keV and 180 keV irradiation, reflecting the reduced diffusion activation energy and faster diffusion within the alloy. The main release peak temperature of 180 keV helium injection is relatively higher than that of 80 keV at the same influence, which is because the irradiation damage of 180 keV, helium formation and entrapment occur deeper. The broadening of the spectra corresponds to different helium trapping sites (He–vacancies, grain boundary) and desorption mechanisms (different He n V m size). The helium retention amount of 80 keV is lower than that of 180 keV, and a saturation limit associated with the irradiation of 80 keV has been reached. The relatively low helium retention proves the better resistance to helium bubbles formation and helium brittleness.

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