Asymmetry of the Nucleon Angular Distributions in the ReactionsHe4(γ, p)H3andHe4(γ, n)He3for65<~Eγ<~170MeV

The cross section for the reaction ${}_{}{}^4{}_{}{}^{}\mathrm{He}(\gamma , pnd)$ is calculated via the quasideuteron mechanism, assuming a ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ Gaussian ground state fitted to the form factor. From the ($\gamma , \mathrm{pnd}$) amplitude the contribution to the reactions ${}_{}{}^4{}_{}{}^{}\mathrm{He}(\gamma , p){}_{}{}^3{}_{}{}^{}\mathrm{H}$, ${}_{}{}^4{}_{}{}^{}\mathrm{He}(\gamma , n){}_{}{}^3{}_{}{}^{}\mathrm{He}$ due to $\mathrm{nd}$ ($\mathrm{pd}$) rescattering to form ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ (${}_{}{}^3{}_{}{}^{}\mathrm{He}$) are calculated. This contribution dominates the high-energy photonucleon cross section. An asymmetry coefficient $\beta =1.51\mathrm{}$ at $E_{\gamma }=120\mathrm{}$ MeV is obtained, close to the observed values.