Three-body correlations for the ground-state decay of the lightest two-proton emitter 6 Be are studied both theoretically and experimentally. Theoretical studies are performed in a three-body hyperspherical-harmonics cluster model. In the experimental studies, the ground state of 6 Be was formed following the α decay of a 10 C beam inelastically excited through interactions with Be and C targets. Excellent agreement between theory and experiment is obtained demonstrating the existence of complicated correlation patterns which can elucidate the structure of 6 Be and, possibly, of the A=6 isobar.

Resonance-decay spectroscopy is used to study particle-unbound excited states produced in interactions of E/A = 10.7 MeV 10 C on Be and C targets. After inelastic scattering, structures associated with excited states in 10 C were observed at 5. 22, 5.29, 6.55, 6.56, 6.57, and 8.4 MeV which decay into the 2p + 2α final state. This final state is created via a number of different decay paths, which include prompt and sequential two-proton decay to the ground state of 8 Be, α decay to 6 Be g.s. , and proton decay to the 2.345-MeV state of 9 B. For the sequential two-proton decay states (5.22 and 6.55 MeV), angular correlations between the first two decay axes indicate that the spin of these states are nonzero. For the prompt two-proton decay of the 5.29-MeV state, the three-body correlations between the two protons and the core are intermediate between those measured for ground-state 6 Be and 45 Fe decays. The 6.55-and 6.57-MeV structures are most probably associated with the same level, which has a 14% two-proton decay branch with a strong "diproton" character and a 86% sequential two-proton decay branch. Correlations between the fragments following the three-body decay of the 2.345-MeV state of 9 B can be approximately described by sequential α decay to the 5 Li intermediate state. The 8.06-and 9.61-MeV 10 B states that decay into the d + 6 Li 2.186 channel are confirmed. Evidence for cluster structure in 13 N is obtained from a number of excited states that decay into the p + 3α exit channel.

The complete three-body correlation pictures are experimentally reconstructed for the two-proton decays of the 6 Be and 45 Fe ground states. We are able to see qualitative similarities and differences between these decays. They demonstrate very good agreement with the predictions of a theoretical three-body cluster model. Validity of the theoretical methods for treatment of the three-body Coulombic decays of this class is thus established by the broad range of lifetimes and nuclear masses spanned by these cases. Implementations for decay dynamics and nuclear structure of 2p emitters are discussed.

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The decay of 10 C excited states to the 2p + 2α exit channel has been studied using an E/A = 10.7 MeV 10 C beam inelastically scattered from a 9 Be target. Levels associated with two-proton decay to the ground state of 8 Be have been observed. These include states at 5.18 and 6.54 MeV which decay by sequential two-proton emission through the long-lived ground state of 9 B. In addition, states at 5.3 and 6.57 MeV were found in which there is no long-lived intermediate state between the two proton emissions. For the 6.57 MeV state, the two protons are preferably emitted on the same side of the decaying 10 C fragment.

The decay of 10 C excited states to the 2p + 2α exit channel has been studied using inelastic excitation of a secondary 10 C beam. The decay sequences leading to the 2p + 2α final state are determined for the previously known levels and for a newly found level at E * = 8.4 MeV. A state at E * = 6.57 MeV is shown to undergo two-proton decay to 8 Be g.s. with strong p-p correlations consistent with the 1 S phase shift. Based on the lack of such correlations for other two-proton decays, this indicates that the correlations are associated with structure of the parent level.

Positronium in the triplet state decays by the emission of three photons and it has been proposed that their simultaneous detection can be used for medical imaging. The three-photon yield has been observed to be enhanced in low O(2) levels in some fluids but has never been measured in biologically relevant liquids. In this study, the delayed three-photon decay yield, at both high and low O(2) levels, has been extracted by fitting the time dependence of the two-photon yield to a set of coupled differential equations. The differential equations, in a simple yet seemingly satisfactory fashion, account for the e(+) capture to form positronium, its decay and the interconversion of the two spin configurations. Our results indicate that the delayed three-photon fraction is 0.25% in water (or blood-like) samples and exhibits no (or exceedingly small) dependence on the dissolved oxygen content. If one assumes that the direct component contributes a fraction expected by annihilation on free electrons (1/372), then the total three-photon fraction is 0.52% in the samples of biological relevance.