The 0+ → 0+ positron double- β decay with emission of two neutrinos in the nuclei 96Ru, 102Pd, 106Cd and 108CdP. K. Raina, A. Shukla, S. Singh, P. K. Rath and J. G. HirschEur. Phys. J. A, 28 1 (2006) 27-36DOI: https://doi.org/10.1140/epja/i2005-10280-2