$^{ 146}$Nd is one of only four (over a total of 35 existing) 2$\beta^-$ decay isotope candidates whose half-lives currently lack experimental limits. The $\alpha$ activity of the $^{ 146}$Sm daughter nuclide allows placement of limits on the 2$\beta$ decay using the $^{ 146}$Nd/$^{ 142}$Nd abundance ratio ($T^{ \beta\beta}_{ 1/2} \gsim 3 \times 10^9$ yr) or direct search for $^{ 146}$Sm with accelerator mass spectrometers ($T^{ \beta\beta}_{ 1/2} \gsim 4.5 \times 10^{ 19}$ yr). With a similar approach, a modest ($\sim$ Gyr) first limit on half-lives for the other unexplored $2\beta$ unstable isotopes and competitive limits (few $10^{ 13}$yr) for $^{ 98}$Mo and $^{ 122}$Sn are also given. Finally, it is shown how the limit $T^{ 0\nu\epsilon\beta^+}_{ 1/2} \gsim 10^{ 15}$ yr for the unexplored $^{ 144}$Sm $0\nu\epsilon \beta^+$ decay may be obtained from the data of a GSO crystal scintillator.
Categories: nucl-ex hep-ph nucl-th