CIII. The neutrons and alpha-particles from the disintegration of9Beby6mevgamma-rays

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Abstract
By measuring the total photo-neutron yield, the cross section for neutron production from 9Be under irradiation with the 19F(p, ξ, γ) radiation is found to be σ t =(12·5 ± 1·2) × 10-28 cm2. The energy spectrum of the two alpha-particles, which are emitted in coincidence in the breakup, has also been studied ; the cross section for all beryllium photo-processes which lead to the emission of two alpha-particles, both of whose energies exceeds 400 kev, is found to be σα=(12·8±2·5) × 10-28 cm2. The near equality of σ t and σα shows that the disintegration rarely proceeds through the 8Be ground state, while a detailed examination of the coincident alpha-particle spectrum suggests that (γ, n) and (γ, α) reactions are present. The (γ, n) transitions are mainly through the 2·9mev excited state of 8Be and the (γ, α) transitions mainly through the 5He ground state, the branching ratio being roughly 1·2 : 1.