Neutron Captureγ-Rays from Fluorine, Sodium, Magnesium, Aluminum, and Silicon

The energies and the absolute intensities of the γ-rays produced by neutron capture in fluorine, sodium, magnesium, aluminum, and silicon have been measured with the aid of a pair spectrometer. Direct transitions to the ground states of the product nuclei are predominant in the γ-ray spectra of fluorine and aluminum. The neutron binding energy in F²⁰ is 6.63±{}0.03 Mev and in Al²⁸, 7.724±{}0.010 Mev. The γ-ray representing the direct transition to the ground state of Na²⁴ was not detected. The interpretation of the magnesium spectrum presents some difficulties. A weak γ-ray with the binding energy of a neutron in Mg²⁵ was detected, but none could be found to correspond to the direct transition to the ground state in Mg²⁶. In silicon, most captures are due to Si²⁸ which produces Si²⁹ by the emission of two γ-rays in cascade. Very weak γ-rays representing direct transitions to the ground states in Si²⁹ and Si³⁰ were detected. Their energies are 8.51±{}0.04 (Si²⁹) and 10.55±{}0.05 Mev (Si³⁰).