Photoprotons from Oxygen, Fluorine, Neon, and Other Light Elements

Abstract

The ($\gamma , p$) reaction in O, F, Ne, and C has been studied with electrons of energies up to 36 MeV. Survey studies were made of the Al, Ar, and B ($\gamma , p$) energy spectra. The reactions were initiated by electrons, and not real photons, but it has been theoretically predicted and received partial experimental verification that there is a one-to-one correspondence between electron- and photon-induced reactions, and that one can assume, when analyzing electron-production yields, that the electron has associated with it a virtual-photon spectrum, similar to the real-photon bremsstrahlung spectrum. The virtual and bremsstrahlung spectra differ, however, in that the virtual-photon spectrum depends on the multipolarity of the induced transition and the angle between the incident electron beam and the emitted disintegration product, while the bremsstrahlung spectrum does not. The electron production yields were analyzed with the use of the $E1\mathrm{}$ virtual-photon spectrum to obtain $\sigma (\gamma , p)$. The proton yields and corresponding cross section of O, F, and Ne contain more than two peaks or resonances. Neon exhibits the most interesting spectrum. It has a series of well-resolved, evenly spaced peaks whose envelope has the usual giant-resonance shape. The peaks occur at laboratory proton energies of 3.20, 3.70, 4.58, 5.80, 6.65, 7.75, 8.65, 9.40, and 11.40 MeV. The final-state properties of the Ne protons from 4 to 10 MeV and the O protons from 9.2 to 12.4 MeV were determined to within 20% by excitation experiments. Angular distribution measurements over a considerable region of the giant resonances are presented for O, F, Ne, and C.