No abstract

No abstract

Nuclear double β − -decays with two neutrinos were observed for many years and a systematic law describing the relation between their half-lives and decay energies was also proposed recently [Phys.Rev. C89, 064603 (2014)]. However, double β + -decay (β + β + ) with emission of both two positrons and two neutrinos has not been observed up to date. In this article, we perform a systematic analysis on the candidates of double β + -decay, based on the 2012 nuclear mass table. Eight nuclei are found to be the good candidates for double β + -decay and their half-lives are predicted according to the generalization of the systematic law to double β + -decay. As far as we know, there is no theoretical result on double β + -decay of nucleus 154 Dy and our result is the first prediction on this nucleus. This is also the first complete research on eight double β + -decay candidates based on the available data of nuclear masses. It is expected that the calculated half-lives of double β + -decay in this article will be useful for future experimental search of double β + -decay.