Speaker
Description
The nuclear two-photon or double-gamma (2γ) decay is a second-order electromagnetic decay process whereby a nucleus in an excited state emits two gamma rays simultaneously. Compared to first-order decay pathways, such as single photon emission or internal conversion, the two-photon decay branch is very small. Ideal cases for this search are 0$^+$ → 0$^+$ transitions, where single photon emission is prohibited. So far this decay was only observed in $^{16}$O, $^{40}$Ca and $^{90}$Zr, where the high transition energy is favourable for the 2γ branch.
At lower energies the 2γ branch becomes prohibitively small for direct γ-ray spectroscopy (10$^{-6-7}$). We have therefore combined Schottky + Isochronous Mass Spectrometry (S+IMS) at the Experimental Storage Ring at GSI. This novel technique allowed us to conduct measurements on the isolated nuclear two-photon decay of the 0$^{+}$ isomers in $^{72}$Ge. $^{98}$Mo and $^{98}$Zr. The branching ratio of $\sim$10$^{-5}$ measured in the case of $^{72}$Ge should also enable direct observation of the γ rays, and initial experiments have been carried out. The obtained mass resolving power will also enable future experiments on nuclear isomers with excitation energies down to ∼100 keV and half-lives as short as ∼1ms.