Evidence of the doubleβdecay of zirconium-96 measured in1.8×109year-old zircons

Molybdenum extracted from geologically old zircons shows evidence for enhanced levels of ${}^{96}\mathrm{Mo},$ resulting from the double β decay of ${}^{96}\mathrm{Zr}.$ Evidence of nuclear fission in ${}^{95}\mathrm{Mo},$ ${}^{97}\mathrm{Mo},$ ${}^{98}\mathrm{Mo},$ and ${}^{100}\mathrm{Mo}$ extracted from the old zircons accompanies the double $\beta$ decay of ${}^{96}\mathrm{Zr},$ and is comparable in magnitude to the excess ${}^{96}\mathrm{Mo}.$ Zircons are excellent minerals for an experiment of this nature, since zircon U-Pb geochronology demonstrates that zircons have remained as closed isotopic systems over eons of time. The experimental data indicate that the half-life of ${}^{96}\mathrm{Zr}$ double $\beta$ decay is $(9.4\mathrm{}\pm 3.2)\times {10}^{18}$ yr and is in good agreement with the theoretically predicted half-life for the ${}^{96}\mathrm{Zr}$ decay to ${}^{96}\mathrm{Mo}$ occurring as a two neutrino decay.