Photoelectric disintegration of ${}^{16}\mathrm{O}$

The photoelectric cross section of ${}^{16}\mathrm{O}(\gamma ,\alpha ){}^{12}\mathrm{C}$ is estimated to be larger than the radiative capture cross section of ${}^{12}\mathrm{C}(\alpha ,\gamma ){}^{16}\mathrm{O}$. The predicted cross section and the angular distribution of the $\alpha$ particle are illustrated for the future experiment. The cross section just above the $\alpha$-particle threshold is found to be dominated by the $E2$ excitation.

Figure 1

Photoelectric cross section for the ${}^{16}\mathrm{O}(\gamma ,\alpha ){}^{12}\mathrm{C}$ reaction as a function of the $\gamma$-ray energy. The solid curve is the result obtained from the potential model. The dashed and dotted curves are the $E1$ and $E2$ components, respectively. The cross section is multiplied by $exp\left(2\pi \eta \right)$ to compensate for the rapid energy variation in the vicinity of the $\alpha$-particle threshold. The vertical thin line at $E_{\gamma }=7.162$ MeV indicates the energy position of the threshold.

Figure 2

Differential cross sections for the ${}^{16}\mathrm{O}(\gamma ,\alpha ){}^{12}\mathrm{C}$ reaction at $E_{\gamma }=8.0$, 8.5, 9.0, and 9.5 MeV. The solid curves are the results obtained from the potential model. The dashed and dotted curves are the pure $E1$ and $E2$ components.

Figure 3

Ratio of $E2$ component to $E1$ in ${}^{16}\mathrm{O}(\gamma ,\alpha ){}^{12}\mathrm{C}$. The solid curve is the result obtained from the potential model. The dot-dashed curve is from the resonance theory [13], of which the value is taken from Fig. 2 of [13].