Electromagnetic character of the competitive $\gamma \gamma /\gamma$-decay from ${}^{137\mathrm{m}}$Ba

Abstract

Second-order processes in physics is a research topic focusing attention from several fields worldwide including, for example, non-linear quantum electrodynamics with high-power lasers, neutrinoless double-$\beta$ decay, and stimulated atomic two-photon transitions. For the electromagnetic nuclear interaction, the observation of the competitive double-$\gamma$ decay from ${}^{137\mathrm{m}}$Ba has opened up the nuclear structure field for detailed investigation of second-order processes through the manifestation of off-diagonal nuclear polarizability. Here we confirm this observation with an $8.7\sigma$ significance, and an improved value on the double-photon versus single-photon branching ratio as $2.62\times 10^{-6}(30)$. Our results, however, contradict the conclusions from the original experiment, where the decay was interpreted to be dominated by a quadrupole-quadrupole component. Here, we find a substantial enhancement in the energy distribution consistent with a dominating octupole-dipole character and a rather small quadrupole-quadrupole element in the decay, hindered due to an evolution of the internal nuclear structure. The implied strongly hindered double-photon branching in ${}^{137\mathrm{m}}$Ba opens up the possibility of the double-photon branching as a feasible tool for nuclear-structure studies on off-diagonal polarizability in nuclei where this hindrance is not present.

arXiv comment12 pages, 5 figures, 2 tabels

References in corpus (8)

• Novel features of nuclear forces and shell evolution in exotic nuclei
• AGATA - Advanced Gamma Tracking Array
• Electric dipole polarizability of ${}^{48}$Ca and implications for the neutron skin
• Investigation of Pygmy Dipole Resonances in the Tin Region
• Hartree Fock Calculations in the Density Matrix Expansion Approach
• Novel shape evolution in Sn isotopes from magic numbers 50 to 82
• Population of isomers in decay of the giant dipole resonance
• Fine structure of the pygmy quadrupole resonance in ${}^{112,114}$Sn isotopes

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• Induced Isotensor Interactions in Heavy-Ion Double-Charge-Exchange Reactions and the Role of Initial and Final State Interactions
• Formal Theory of Heavy Ion Double Charge Exchange Reactions
• A new scheme for isomer pumping and depletion with high-power lasers