Fine Structure in the Energy Spectra of Photoprotons fromHe4

The energy spectra of the photoprotons from ${\mathrm{He}}^4$ irradiated with 31 and 32-Mev bremsstrahlung were studied by means of nuclear photoemulsions in $\Delta E_{\gamma }$ steps of 0.133 Mev. In the region of the giant resonance several peaks have been distinguished. The more evident of these have widths less than 0.5 Mev and are located at ${\mathrm{He}}^4$ excitation energies of 24.7±0.2 and 26.1±0.1 Mev. Previous experiments on the photoproton spectra from ${\mathrm{He}}^4$ could not give evidence of these narrow resonances because the spectra were examined in energy steps much larger than the width of these resonances.