The Energy Spectrum of Neutrons from a Po—Be Source

The energy spectrum of neutrons emitted by a Po—Be source has been determined by the photographic emulsion method. The results agree, on certain assumptions, with the existence of energy levels in the ${\mathrm{C}}^{12}$ nucleus at 2.5, 4.5, and 7.1 Mev. The last two of these are consistently found by other workers, but the existence of the first is sometimes disputed. Possible reasons for the apparent discrepancies in the evidence on this point are discussed.