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- Title
Observation of the competitive double-gamma nuclear decay.
- Authors
Walz, C.; Scheit, H.; Pietralla, N.; Aumann, T.; Lefol, R.; Ponomarev, V. Yu.
- Abstract
The double-gamma (γγ)-decay of a quantum system in an excited state is a fundamental second-order process of quantum electrodynamics. In contrast to the well-known single-gamma (γ)-decay, the γγ-decay is characterized by the simultaneous emission of two γ quanta, each with a continuous energy spectrum. In nuclear physics, this exotic decay mode has only been observed for transitions between states with spin-parity quantum numbers Jπ = 0+ (refs 1, 2, 3). Single-gamma decays-the main experimental obstacle to observing the γγ-decay-are strictly forbidden for these 0+ → 0+ transitions. Here we report the observation of the γγ-decay of an excited nuclear state (Jπ = 11/2−) that is directly competing with an allowed γ-decay (to ground state Jπ = 3/2+). The branching ratio of the competitive γγ-decay of the 11/2− isomer of 137Ba to the ground state relative to its single γ-decay was determined to be (2.05 ± 0.37) × 10−6. From the measured angular correlation and the shape of the energy spectra of the individual γ-rays, the contributing combinations of multipolarities of the γ radiation were determined. Transition matrix elements calculated using the quasiparticle-phonon model reproduce our measurements well. The γγ-decay rate gives access to so far unexplored important nuclear structure information, such as the generalized (off-diagonal) nuclear electric polarizabilities and magnetic susceptibilities.
- Subjects
GAMMA decay; QUANTUM mechanics; PARITY (Physics); QUANTUM electrodynamics; QUANTUM numbers; GROUND state (Quantum mechanics); QUASIPARTICLE-phonon model; NUCLEAR structure
- Publication
Nature, 2015, Vol 526, Issue 7573, p406
- ISSN
0028-0836
- Publication type
Article
- DOI
10.1038/nature15543