The interaction of an E/A=70-MeV (7)Be beam with a Be target was used to populate levels in (6)Be following neutron knockout reactions. The three-body decay of the ground and first excited states into the α+p+p exit channel were detected in the High Resolution Array. Precise three-body correlations extracted from the experimental data allowed us to obtain insight into the mechanism of the three-body democratic decay. The correlation data are in good agreement with a three-cluster-model calculation and thus validate this theoretical approach over a broad energy range.
A B S T R A C TEfficiency corrected single ratios of neutron and proton spectra in central 112 Sn+ 112 Sn and 124 Sn+ 124 Sn collisions at 120 MeV/u are combined with double ratios to provide constraints on the density and momentum dependencies of the isovector mean-field potential. Bayesian analyses of these data reveal that the isoscalar and isovector nucleon effective masses, * − * are strongly correlated. The linear correlation observed in * − * yields a nearly independent constraint on the effective mass splitting Δ * = ( * − * )∕ = −0.05 +0.09 −0.09 . The correlated constraint on the standard symmetry energy, 0 and the slope, at saturation density yields the values of symmetry energy ( ) = 16.8 +1.2 −1.2 MeV at a sensitive density of ∕ 0 = 0.43 +0.05 −0.05 .
8 C is found to decay to four protons and an α particle in two 2p emission steps. The correlations between the protons in the first step ( 8 C to 6 Be) exhibit a significant enhancement in the region of the decay phase space where the two protons have small relative energy, a region sometimes called the diproton region. The decay of the isobaric analog of 8 C in 8 B is also found to decay by 2p emission. This is the first case of isospin-allowed 2p decay between isobaric analog states.
We probe the momentum dependence of the isovector mean-field potential by comparing the energy spectra of neutrons and protons emitted in 112 Sn+ 112 Sn and 124 Sn+ 124 Sn collisions at incident energies of E/A=50 and 120 MeV. We achieve experimental precision that discriminates between different momentum dependencies for the symmetry mean-field potential. Comparisons of the experimental results to Improved Quantum Molecular Dynamics model calculations with Skyrme Interactions indicate small differences between the neutron and proton effective masses.
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