ββ Decay at the TUNL Low-Background Counting Facility
The TUNL-ITEP ββ decay setup was originally located in the TUNL Low-Background Counting Facility (LBCF), a well-shielded room located in the basement of the Duke University Physics Department. This room, known casually as "the cave", has a concrete ceiling several feet thick. The three floors above the laboratory as well as the roof of the building provide additional shielding. Overall, there was approximately 10 mwe overburden reducing the cosmic-ray flux.
The ββ decay setup was used in the TUNL LBCF to investigate the ββ decays of 100Mo and 150Nd to excited states of 100Ru and 150Sm respectively, as well as double-electron capture (ECEC) to excited final states (see Kidd et al.).
The double beta decay of 100Mo to the excited 0+1 state of 100Ru was successfully observed and a half-life of [6.0-1.1+1.9(stat) ± 0.6(syst)] × 1020 years was determined (see Hornish et al.). Limits were placed on decays to higher excited states. Further measurements were done from 2003 to 2005 with an improved determination of the coincidence efficiency, which lowered the systematic uncertainty. These results have been submitted to Nuclear Physics A.
The ββ decay of 150Nd to excited states of 150Sm was also investigated, though it was found that the enriched source was contaminated with 232Th decay products. The background from these contaminants was too high in our regions of interest to extract a competitive half-life limit. The source was returned to Oak Ridge National Laboratory for purification in late 2007, and has recently been reinstalled at our underground facility.
Finally, ECEC on 112Sn to the 1871 keV excited state of 112Cd was investigated for about 100 days.
created by M.F. Kidd