Search for double β decays of 96Ru and 104Ru

The investigation of neutrinoless 2EC ad ECβ+ processes could refine the understanding of contribution of the right-handed currents to the neutrinoless double β- decay. Therefore developments of the experimental technique to search for such processes are strongly required.

96Ru is one of only six potentially 2β+ active nuclei. The energy of double beta decay is Q=(27188) keV. Among 2β+ candidates, it is one of the nuclide which has considerably high natural abundance (5.54%).

It should be also noted that in the 0ν2EC process with capture of one electron from the K shell and a second one from one of the L shells, the energy release of (26958) keV is close to the energy of the excited level of 96Mo with Eexc=2700 keV. In a case of 2EC from two L shells the energy release is (27138) keV which is equal, within errors, to the energy of the other excited level at 2713 keV. Such a coincidence can give a resonant enhancement of the neutrinoless KL and 2L capture in result of energy degeneracy, thus an enhancement of the signal rate by some orders of magnitude is predicted.

Ruthenium with natural isotopic composition of 99.99% grade in form of tablets, with mass 8.5 g each (density about 8.7 g/cm3) for a total mass of 473 g was measured at the Ge facility at LNGS with a p-type HPGe detector (468 cm3).