Observation of the competitive double-gamma nuclear decay

摘要: The exotic double-gamma nuclear decay has been observed in cases where the usual single-gamma is forbidden, but now a of excited 137Ba reported that competition with decay. Most decays quantum states involve emission one photon, processes first predicted by Nobel laureate Maria Goeppert-Mayer more than 75 years ago, emitting two photons can occur. An analogous process atomic nuclei decay, which forbidden. In an experimental tour de force, Heiko Scheit and colleagues observe Through caesium-137, state barium-137 populated. Monitoring emissions for 50 days carefully excluding alternative explanations their data, authors are able to unambiguously measure competitive Precise measurements rate promise give access structure information elusive other methods. (γγ)-decay system fundamental second-order electrodynamics. contrast well-known (γ)-decay, γγ-decay characterized simultaneous γ quanta, each continuous energy spectrum. physics, this mode only transitions between spin-parity numbers Jπ = 0+ (refs 1, 2, 3). Single-gamma decays—the main obstacle observing γγ-decay—are strictly forbidden these → transitions. Here we report observation (Jπ 11/2−) directly competing allowed γ-decay (to ground 3/2+). branching ratio 11/2− isomer relative its single was determined be (2.05 ± 0.37) × 10−6. From measured angular correlation shape spectra individual γ-rays, contributing combinations multipolarities radiation were determined. Transition matrix elements calculated using quasiparticle–phonon model reproduce our well. gives so far unexplored important information, such as generalized (off-diagonal) electric polarizabilities magnetic susceptibilities3.