Average and recommended half-life values for two-neutrino double beta decay: upgrade-2019

All existing positive results on two neutrino double beta decay and two neutrino double electron capture in different nuclei were analyzed. Using the procedure recommended by the Particle Data Group, weighted average values for half-lives of ${}^{48}$Ca, ${}^{76}$Ge, ${}^{82}$Se, ${}^{96}$Zr, ${}^{100}$Mo, ${}^{100}$Mo - ${}^{100}$Ru ($0_1^{+}$), ${}^{116}$Cd, ${}^{130}$Te, ${}^{136}$Xe, ${}^{150}$Nd, ${}^{150}$Nd - ${}^{150}$Sm ($0_1^{+}$), ${}^{238}$U, ${}^{78}$Kr and ${}^{124}$Xe were obtained. Existing geochemical data were analyzed and recommended values for half-lives of ${}^{128}$Te and ${}^{130}$Ba are proposed. I recommend the use of these results as the most currently reliable values for half-lives.