Electron capture branching ratios for the odd–odd intermediate nuclei in double-beta decay using the TITAN ion trap facility

Abstract

We suggest a measurement of the electron capture (EC) branching ratios for the odd–odd intermediate nuclei in double-beta (β– β–) decay using the new ion trap facility TITAN at the TRIUMF radioactive beam facility. The EC branching ratios are important for evaluating the nuclear matrix elements involved in the β– β– -decay for both, the 2ν and the 0ν-decay mode. Especially the neutrinoless (0νββ) mode is presently at the center of attention, as it probes the Majorana character of the neutrino, and if observed unambiguously, knowledge of the nuclear matrix elements are the key for determining the neutrino mass. The EC branches are in most cases suppressed by several orders of magnitude relative to their β– -counterparts owing to much lower decay energies, and are, therefore, either poorly known or not known at all. Here, the traditional methods of producing the radioactive isotope through irradiation of a suitable target and then measuring the K-shell X-rays have reached a limit of sensitivity. In this note, we will describe a novel technique to measure the EC branching ratios, where the TITAN ion traps and the ISAC radioactive beam facility at TRIUMF are the central components. This approach will increase the sensitivity limit because of significantly reduced background levels. Seven cases will be discussed in detail and connections to hadronic charge-exchange reactions will be made. For most of these, the daughter isotopes are β– β– -decay nuclei that are presently under intense experimental investigations. These are [Formula: see text]PACS Nos.: 23.40.–s, 23.40.Hc, 29.30.Kv, 29.25.Rm, 14.60.Pq